IGCSE Chemistry Past Papers by Topic with Solutions | Free Resources

IGCSE Chemistry Past Papers by Topic with Solutions

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1.1.1 Properties of Solids Liquids and Gases Paper 4 IGCSE Chemistry Topic Questions

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Q1: (a) Use ideas about the movement and arrangement of particles to explain why:
- Solids have a definite volume and shape
- Liquids have a definite volume but no definite shape
- Gases have no definite volume or shape
........................................................................................................................................................................ [4]
........................................................................................................................................................................ [4]
........................................................................................................................................................................

Mark scheme: (a) Any four from: [4]
- Solids: particles close together / no space between particles / particles arranged regularly / particles touching
- Solids: particles only vibrate
- Allow: particles cannot move / particles in fixed positions
- Liquids: particles can slide over each other / particles have limited movement
- Ignore: particles can move unqualified
- Liquids: particles close together / particles not arranged regularly / particles arranged randomly / particles not in fixed positions
- Ignore: particles further apart than in solids
- Gases: particles far apart / particles arranged randomly
- Gases: particles can move everywhere / particles move anywhere / particles move randomly

Note: It must be clear which state is being referred to

Note: There must be reference to particles (or atoms / molecules / ions) in the answer to gain marks

Solution

Solids have a definite volume and shape because the particles are close together, arranged regularly, and can only vibrate in fixed positions.

Liquids have a definite volume but no definite shape because the particles are close together, arranged randomly, and can slide over each other with limited movement.

Gases have no definite volume or shape because the particles are far apart, arranged randomly, and can move everywhere or randomly.

1.1.2 Structure of Solids Liquids and Gases Paper 4 IGCSE Chemistry Topic Questions

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Q1: (a) Complete the table, using ticks (✔) and crosses (✘), to describe the properties of gases, liquids and solids.

Tip: swipe sideways to see the full table →

state of matter	particles are touching	particles have random movement	particles are regularly arranged
gas
liquid
solid

Mark Scheme:

1 mark for each correct row.

Tip: swipe sideways to see the full table →

State	touching	random movement	regularly arranged
Gas		✔
Liquid	✔	✔
Solid	✔		✔

1.1.3 State Changes Paper 4 IGCSE Chemistry Topic Questions

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Q1: Substances can change state.
- (i) Boiling and evaporation are two ways in which a liquid changes into a gas.
  Describe two differences between boiling and evaporation.
  1. ..........................................................................................................................................
  2. ....................................................................................................................................[2]..
- (ii) Name the change of state when:
  - A gas becomes a liquid: ................................................................................................
  - A solid becomes a gas: ..........................................................................................[2]......
Mark Scheme:
- (i):
  - Boiling happens at a specific temperature (1)
  - Boiling has bubbles (1)
- (ii):
  - A gas becomes a liquid: condensation (1)
  - A solid becomes a gas: sublimation (1)

Solution

(i) Boiling occurs at a fixed temperature while evaporation occurs at any temperature. Boiling happens throughout the liquid with bubbles, while evaporation only happens at the surface without bubbles.

(ii) A gas becomes a liquid by condensation. A solid becomes a gas by sublimation.

1.1.4 Effect of Temperature and Pressure on Gases Paper 4 IGCSE Chemistry Topic Questions

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Q1: Substances can change state.
- (i) Boiling and evaporation are two ways in which a liquid changes into a gas.
  Describe two differences between boiling and evaporation.
  1. ..........................................................................................................................................
  2. ..........................................................................................................................................
  [2]
- (ii) Name the change of state when:
  - A gas becomes a liquid: ................................................................................................
  - A solid becomes a gas: ................................................................................................
  [2]
Mark Scheme:
- (i):
  - Boiling happens at a specific temperature (1)
  - Boiling has bubbles (1)
- (ii):
  - A gas becomes a liquid: condensation (1)
  - A solid becomes a gas: sublimation (1)

Solution

(i) Boiling occurs at a fixed temperature while evaporation can happen at any temperature. Boiling occurs throughout the liquid with bubble formation, while evaporation occurs only at the surface without bubbles.

(ii) A gas becomes a liquid by condensation. A solid becomes a gas by sublimation.

1.1.2 Diffusion Paper 4 IGCSE Chemistry Topic Questions

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Q1: The elements shown are gases at room temperature and pressure (Hydrogen, Nitrogen, Oxygen, Chlorine).
- (i) Describe why these gases diffuse.
  ................................................................................................................ [1]
- (ii) State which of these four gases has the highest rate of diffusion. Explain your answer.
  - Gas: ................................................................................................................
  - Explanation: ................................................................................................................ [2]
Mark Scheme:
- (i) random motion of molecules / particles. [1]
- (ii) Hydrogen – lowest relative molecular mass. [2]

Q2: The rate of diffusion of a gas was studied.

The following data shows the relative molecular masses (Mr) and rates of diffusion of the gases:

Tip: swipe sideways to see the full table →

Gas	Temperature (°C)	Rate of diffusion (cm³/min)
Nitrogen	25	1.00
Chlorine	25	0.63
Nitrogen	50	1.05

(i) Explain why nitrogen gas diffuses faster than chlorine gas.
........................................................................................................ [2]
(ii) Explain why the nitrogen gas diffuses faster at the higher temperature.
........................................................................................................ [1]

Mark Scheme:
- (i) nitrogen has smaller Mr; nitrogen molecules move faster than chlorine molecules (must be comparative). [2]
- (ii) At higher temperature molecules move faster / have more energy. [1]

Solution

Q1 (i): Gases diffuse because their molecules are in constant random motion.

Q1 (ii): Hydrogen diffuses the fastest as it has the lowest relative molecular mass, so its particles move faster.

Q2 (i): Nitrogen diffuses faster than chlorine because it has a smaller Mr and its molecules move faster (comparison needed).

Q2 (ii): Nitrogen diffuses faster at higher temperature because molecules have more energy and move faster.

2.1.2 Atomic Structure Basics Paper 4 IGCSE Chemistry Topic Questions

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Q1: Atoms and ions are made from small particles called electrons, neutrons, and protons.

(a) Complete the table:

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Particle	Relative Charge	Relative Mass
Electron	-1	1/1840
Neutron	_	_
Proton	_	_

(b) Complete the table for atoms and ions A, B, and C:

Tip: swipe sideways to see the full table →

Atom or Ion	Number of Electrons	Number of Neutrons	Number of Protons	Symbol
A	18	_	20	⁴²₂₀Ca²⁺
B	_	18	_	³⁵₁₇Cl^1-
C	18	16	16

Mark Scheme:

(a):

Particle	Relative Charge	Relative Mass
Electron	-1	1/1840
Neutron	0	1
Proton	+1	1

(b):

Atom or Ion	Details
A	Neutrons = 42 − 20 = 22; Symbol: ⁴²₂₀Ca²⁺ [1]
B	Protons = 17; Electrons (for Cl⁻) = 18; Neutrons = 35 − 17 = 18; Symbol: ³⁵₁₇Cl⁻ [1]
C	Protons = 16; Electrons = 18 (so 2− ion); Neutrons = 16 ⇒ mass 32; Symbol: ³²₁₆S²⁻ [1]

Solution

(a) Neutron: charge 0, relative mass 1. Proton: charge +1, relative mass 1. (Electron already given: −1, 1/1840.)

(b)

A: Protons = 20, Electrons = 18 ⇒ Ca²⁺; Neutrons = 42 − 20 = 22; Symbol ⁴²₂₀Ca²⁺.
B: For ³⁵₁₇Cl⁻: Protons = 17, Neutrons = 35 − 17 = 18, Electrons = 18; Symbol ³⁵₁₇Cl⁻.
C: Protons = 16 (sulfur), Electrons = 18 ⇒ S²⁻, Neutrons = 16 ⇒ mass 32; Symbol ³²₁₆S²⁻.

2.3 Isotopes Basics Paper 4 IGCSE Chemistry Topic Questions

Q1 (a): Sulfur exists as a number of different isotopes. What is meant by the term isotopes?

Atoms with the same number of protons or atoms of the same element or atoms with the same atomic number [1]
Atoms with a different number of neutrons or atoms with a different mass number or atoms with a different nucleon number [1]

2.3 Isotopes Percentage Abundance Paper 4 IGCSE Chemistry Topic Questions

Question 1:
Table 2.2 shows the relative abundance of the two naturally occurring isotopes of copper.

Table 2.2

Isotope ⁶³Cu ⁶⁵Cu

Relative abundance 70% 30%

Calculate the relative atomic mass of copper to one decimal place.

Relative atomic mass = ................................................................. [2]
Mark Scheme:
- M1: (63 × 70) + (65 × 30) = 6360 (1)
- M2: 6360 / 100 = 63.6 (1)
[2]

Isotope	⁶³Cu	⁶⁵Cu
Relative abundance	70%	30%

2.4 Ions and Ionic Bonds Paper 4 IGCSE Chemistry Topic Questions

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Q1: State the meaning of the term ionic bonding. [2]

..........................................................................................................................................

..........................................................................................................................................
Mark Scheme:
- Strong force of attraction (1)
- Between + and – ions / between oppositely charged ions (1)

Solution

Ionic bonding is the strong electrostatic force of attraction between oppositely charged positive and negative ions.

2.4.1 Ionic Compounds Physical Properties Paper 4 IGCSE Chemistry Topic Questions

Question Paper 1:
Give three physical properties of ionic compounds.
1. ..........................................................................................................................................
2. ..........................................................................................................................................
3. ..........................................................................................................................................
[3]
Mark Scheme:
- High melting point or boiling point
- Hard
- Brittle
- Soluble in water / insoluble in organic solvents
- Conduct electricity in liquid state or in aqueous solution
- Non-conductors or poor conductors (when solid)
[3]

2.5 Simple Molecules and covalent Compounds Dot Cross Diagrams Paper 4 IGCSE Chemistry Topic Questions

Question: Complete the dot-and-cross diagram to show the arrangement of electrons in a molecule of ester Y.
Diagram:

Mark Scheme:

M1: Two crosses on the inner circle circumference labeled 'O' (up and down).
M2: Two dots on the inner circle circumference labeled 'C' (up and down).
M3: Correct arrangement of all other circles.

2.7 Metallic Bonding Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe the metallic bonding in zinc and then explain why it is a good conductor of electricity. [4]

Mark Scheme:

Positive ions / cations [1] (Not nuclei / atoms)
Delocalised / free / mobile or sea of electrons [1]
Bond is attraction between (positive) ions and delocalised electrons [1]
It is a good conductor because there are delocalised / free / mobile electrons [1] (Note: must indicate electrons are moving / carry charge)

2.6.1 Macromolecule Diamond / Graphite/ Silicon Dioxide Paper 4 IGCSE Chemistry Topic Questions

Question Paper 1:
Diamond and graphite are different solid forms of carbon. The carbon atoms in diamond and graphite are arranged in different ways.
- (a) State the number of covalent bonds each carbon atom has in diamond. [1]
- (b) State the term used to describe the structure of diamond. [1]
- (c) Name an oxide that has a similar structure to diamond. [1]
- (d) Describe the arrangement of atoms in graphite. [2]
- (e) Explain how graphite conducts electricity. [1]
Mark Scheme:
- (a): 4 (1)
- (b): Giant covalent (1)
- (c): Silicon dioxide (1)
- (d):
  - M1: Layers
  - M2: Hexagonal (rings of carbon) [2]
- (e): Mobile electrons (1)

2.7 Metallic Bonding Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe the metallic bonding in zinc and then explain why it is a good conductor of electricity. [4]

Mark Scheme:

Positive ions / cations [1] (Not nuclei / atoms)
Delocalised / free / mobile or sea of electrons [1]
Bond is attraction between (positive) ions and delocalised electrons [1]
It is a good conductor because there are delocalised / free / mobile electrons [1] (Note: must indicate electrons are moving / carry charge)

3.1 / Molecular Formular and Empirical Formula Paper 4 IGCSE Chemistry Topic Questions

Q1: Magnesium phosphate contains magnesium ions, Mg²⁺, and phosphate ions, PO₄^3–. Deduce the formula of magnesium phosphate. [1]

Mark Scheme:

Mg₃(PO₄)₂ [1]

Q2: Sulfur dioxide reacts with aqueous sodium sulfite to produce a compound with the following composition by mass: 29.1% Na, 40.5% S and 30.4% O. Calculate the empirical formula of this compound. Empirical formula = .............................. [3]

Mark Scheme:

29.1 / 23, 40.5 / 32, 30.4 / 16 or 1.2(65), 1.2(65), 1.9 [1]
1:1:1.5 [1]
Empirical formula: Na₂S₂O₃ [1]

Q3:

(a) Compound X has the following composition by mass:

H, 3.66%; P, 37.80%; O, 58.54%

Calculate the empirical formula of compound X.

empirical formula = .............................. [2]

(b) Compound Y has the empirical formula H₃PO₄ and a relative molecular mass of 98.
Deduce the molecular formula of compound Y.

molecular formula = .............................. [1]

Mark Scheme:

(a)

M1: H = 3.66 / 1, P = 37.80 / 31, O = 58.54 / 16
OR H = 3.66, P = 1.22, O = 3.66
OR H:P:O = 3:1:3 [1]

M2: H₃PO₃ [1]
(b): H₃PO₄ [1]

3.1.2 /Formula of Ions and Compounds Paper 4 IGCSE Chemistry Topic Questions

Q1: Magnesium phosphate contains magnesium ions, Mg²⁺, and phosphate ions, PO₄^3–. Deduce the formula of magnesium phosphate. [1]

Mark Scheme:

Mg₃(PO₄)₂ [1]

3.2 Word Equations and Symbol Equations Paper 4 IGCSE Chemistry Topic Questions

Q1: Element X is a Group III metal. It burns in air to form an oxide X₂O₃.
Write a symbol equation for this reaction.
.............................................................................................................................................. [2]

Mark Scheme:

Formulae [1]
Balance, 4X + 3O₂ → 2X₂O₃ [1]

Q2: Complete the word equation for this reaction.

Sodium bromide + Chlorine → .............................. + ..............................

Mark Scheme:

calcium oxide (1)
carbon dioxide (1)

3.3 Calculating Moles/ Concentration Paper 4 IGCSE Chemistry Topic Questions

Question: The equation for the reaction is shown:

2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

Calculate the concentration of NaOH(aq) formed, in g/dm³, when 0.345 g of sodium is added to 50.0 cm³ of distilled water. Assume there is no change in volume.
Use the following steps:

● Calculate the number of moles of Na added.
= .............................. mol
● Determine the number of moles of NaOH formed.
= .............................. mol
● Calculate the concentration of NaOH in mol/dm³.
concentration of NaOH = .............................. mol/dm³
● Determine the Mr of NaOH and calculate the concentration of NaOH in g/dm³.
concentration of NaOH = .............................. g/dm³

Mark Scheme:

M1: mol Na = 0.345 / 23 = 0.015(00) (1)
M2: mol NaOH = M1 = 0.015(00) (1)
M3: M2 × 1000 / 50 = 0.015(00) × 20 = 0.3(00) (1)
M4: Mr NaOH = 40 (1)
M5: M4 × M3 = 40 × 0.3 = 12.(0) (g/dm³) (1)

3.3 Molar Gas Volume Paper 4 IGCSE Chemistry Topic Questions

Question: Calculate the volume of oxygen, measured at r.t.p., which is formed when 1.60 g of CuO reacts as shown in the equation:

4CuO → 2Cu₂O + O₂

Answer: .................................................... dm³ [3]
Mark Scheme:

M1: mol CuO = (1.60 ÷ 80) = 0.02(00) mol [1]
M2: mol O₂ = (M1 ÷ 4 = 0.02 ÷ 4) = 0.005(00) mol [1]
M3: vol O₂ = M2 × 24.0 = 0.005 × 24.0 = 0.12(0) dm³ [1]

3.4 Excess / Limiting Reactants Paper 4 IGCSE Chemistry Topic Questions

Question: Propanol reacts with methanoic acid to form the ester propyl methanoate.

CH₃CH₂CH₂OH + HCOOH → HCOOCH₂CH₂CH₃ + H₂O

4.0 g of methanoic acid was reacted with 6.0 g of propanol.

(i) Calculate the Mr of methanoic acid = ........................................ [1]
(ii) Calculate the Mr of propanol = ........................................ [1]
(iii) Determine which one is the limiting reagent. Show your reasoning.

.............................................................................................................................................
.............................................................................................................................................
............................................................................................................................................. [2]

Mark Scheme:

M1: moles of CH₃CH₂CH₂OH = 0.1 [1]
M2: moles of HCOOH = 0.087 (0.09) and limiting reagent is methanoic acid [1]

3.5 Percentage Yield / Percent by Mass Paper 4 IGCSE Chemistry Topic Questions

Question:

(i) 5.95 g of cobalt(II) carbonate were added to 40 cm³ of hydrochloric acid, concentration 2.0 mol / dm³.
Calculate the maximum yield of cobalt(II) chloride-6-water and show that the cobalt(II) carbonate was in excess.

CoCO₃ + 2HCl → CoCl₂ + CO₂ + H₂O
CoCl₂ + 6H₂O → CoCl₂.6H₂O

- maximum yield:
- number of moles of HCl used = ........................................
- number of moles of CoCl₂ formed = ........................................
- number of moles of CoCl₂.6H₂O formed = ........................................
- mass of one mole of CoCl₂.6H₂O = 238 g
- maximum yield of CoCl₂.6H₂O = ........................................ g

Mark Scheme:

number of moles of HCl used = 0.04 × 2 = 0.08 [1]
number of moles CoCl₂ formed = 0.04 [1]
number of moles CoCl₂.6H₂O formed = 0.04 [1]
maximum yield of CoCl₂.6H₂O = 9.52 g [1]
Allow: 9.5
Allow: ecf on number of moles of HCl

4.1 Electrolysis Basics Paper 4 IGCSE Chemistry Topic Questions

Electrode Question

Q1:
- a State two reasons why carbon (graphite) is suitable to use as an electrode.[2]
- Current Flow Question
  b Name the particle responsible for the conduction of electricity in the metal wires used in a circuit.[1]

Mark Scheme:
- a
  - M1 inert (1)
  - M2 good conductor of electricity (1)
  [2]
- b electron [1]

4.1.3 Electrolysis of Molten Compounds Paper 4 IGCSE Chemistry Topic Questions

Q1: Molten potassium bromide can be electrolysed. Predict the products of this electrolysis at:
the anode ..................................................................................................................................
the cathode .............................................................................................................................. [2].
Mark Scheme:
the anode: bromine / Br₂ ................................................................................................................. 1
the cathode: potassium / K ...................................................................................................................... [1].

4.1.4.1 Electrolysis of Aqueous Compounds [ Concentrated] Paper 4 IGCSE Chemistry Topic Questions

Question 1: This question is about electrolysis.

Concentrated hydrochloric acid is electrolysed using the apparatus shown.[ DIgram has not been included here. KIndly refer to tghe paper 0620_w21_qp_41-q3]
(a) Chloride ions are discharged at the anode.
- (i) Complete the ionic half-equation for this reaction.
  .......... Cl^–(aq) → ..........(g) + .......... e^– [2]
- (ii) State whether oxidation or reduction takes place. Explain your answer.
  ..................................................................................................................
  .................................................................................................................. [1]
(b) Describe what is seen at the cathode.
..................................................................................................................
.................................................................................................................. [1]
(c) Write the ionic half-equation for the reaction at the cathode.
..................................................................................................................
.................................................................................................................. [2]
(d) The pH of the electrolyte is measured throughout the experiment.
- (i) Suggest the pH of the electrolyte at the beginning of the experiment.
  .................................................................................................................. [1]
- (ii) State how the pH changes, if at all, during the experiment.
  Explain your answer.
  ..................................................................................................................
  ..................................................................................................................
  .................................................................................................................. [2]

Mark Scheme:
- 3(a)(i):
  - 2Cl ^– → Cl ₂ + 2e^– (1)
  - Rest of the equation (1)
  - Total: 2
- 3(a)(ii):
  - Oxidation AND lose electrons (1)
  - Total: 1
- 3(b):
  - Effervescence (of colourless gas) (1)
  - Total: 1
- 3(c):
  - 2H⁺ + 2e^– → H₂
  - H⁺ + e^– as the only species on LHS (1)
  - Rest of the equation fully correct (1)
  - Total: 2
- 3(d)(i):
  - (1)
  - Total: 1
- 3(d)(ii):
  - M1: Increase (1)
  - M2: H⁺ ions being removed (1)
  - Total: 2

4.1.4.2 Electrolysis of Aqueous Compounds [ Dilute] Paper 4 IGCSE Chemistry Topic Questions

Q1: A student carries out an electrolysis experiment using the apparatus shown.
- [Diagram not included here. But it has two carbon electrodes and dilute aqueous sodium chloride as the electrolyte. Diagram can be found at: 0620/42/M/J/21-q4]
- The student uses dilute aqueous sodium chloride.
  - (a) State the name given to any solution which undergoes electrolysis.
    .............................................................................................................................................. [1]
  - (b) Hydroxide ions are discharged at the anode.
    - (i) Complete the ionic half-equation for this reaction.
      ..........OH–(aq) → ........................... + O2 (g) + 4e– [2]
    - (ii) Explain how the ionic half-equation shows the hydroxide ions are being oxidised.
      ....................................................................................................................................... [1]
  - (c) Describe what the student observes at the cathode.
    .............................................................................................................................................. [1]
  - (d) Write the ionic half-equation for the reaction at the cathode.
    .............................................................................................................................................. [2]

Mark Scheme:
- (a) electrolyte [1]
- (b)(i) 4OH⁻ → 2H₂O + O₂ + 4e⁻
  - balance of charge (1)
  - rest of equation (1)
  [2]
- (b)(ii) (OH⁻(aq) ions) lose electrons [1]
- (c) fizzing [1]
- (d) 2H⁺ + 2e⁻ → H₂
  - species correct (1)
  - fully correct equation (1)
  [2]

4.1.5 Electrolysis of Brine Paper 4 IGCSE Chemistry Topic Questions

Q1: Brine is concentrated aqueous sodium chloride.
(i) Name three substances which are manufactured by passing electricity through brine.
1 ..........................................................................................................................................
2 ..........................................................................................................................................
3 .......................................................................................................................................... [3]
Mark Scheme:
(i) hydrogen
chlorine
sodium hydroxide ................................................................................................................. 3
4(e)(ii) sodium ...................................................................................................................... 1

4.1.6 Electrolysis of Dilute Sulfuric Acid Paper 4 IGCSE Chemistry Topic Questions

Q1:
(a) Dilute sulfuric acid is electrolysed using the apparatus shown in the diagram.
(i) State what is meant by the term electrolysis.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [2]
(ii) Explain why inert electrodes are used.
.............................................................................................................................................
....................................................................................................................................... [1]
(iii) Name the products formed at each electrode.
negative electrode ..............................................................................................................
positive electrode ................................................................................................................ [2]
(iv) Write an ionic half‑equation for the reaction at the negative electrode.
....................................................................................................................................... [2]
Mark Scheme:
(a)(i) breakdown by (the passage of) electricity (1)
of an ionic compound in molten/aqueous (state) (1) ................................................................................. 2
(a)(ii) they do not react ...................................................................................................................... 1
(a)(iii) negative electrode: hydrogen (gas) (1)
positive electrode: oxygen (gas) (1)
(a)(iv) H⁺ + e^- as the only species on the left (1)
equation fully correct (1) ...................................................................................................................... 2
2H⁺ + 2e^- → H₂ (scores 2)

4.1.7 Electrolysis of Copper Sulfate Paper 4 IGCSE Chemistry Topic Questions

Qp1:
Copper has the structure of a typical metal. It has a lattice of positive ions and a “sea” of mobile electrons. The lattice can accommodate ions of a different metal.
(a) Aqueous copper(II) sulphate solution can be electrolysed using carbon electrodes. The ions present in the solution are as follows.
Cu²⁺(aq), SO₄^2-(aq), H⁺(aq), OH^-(aq)
(i) Write an ionic equation for the reaction at the negative electrode (cathode).
(ii) A colourless gas was given off at the positive electrode (anode) and the solution changes from blue to colourless.
Explain these observations.
(b) Aqueous copper(II) sulphate can be electrolysed using copper electrodes. The reaction at the negative electrode is the same but the positive electrode becomes smaller and the solution remains blue.
(i) Write a word equation for the reaction at the positive electrode.
(ii) Explain why the colour of the solution does not change.
(iii) What is the large scale use of this electrolysis?
Mark Scheme:
(a) (i) Cu²⁺ + 2e^- = Cu [1]
(ii) gas is oxygen [1]
(copper(II) sulphate) changes to sulphuric acid
or copper ions removed from solution [1]
(b) (i) copper atoms - electrons = copper ions
accept correct symbol equation [1]
(ii) concentration of copper ions does not change or
amount or number of copper ions does not change [1]
copper ions are removed and then replaced
or copper is transferred from anode to cathode [1]
(iii) refining copper or plating (core)
or extraction of boulder copper [1]

4.1.7 Electrolysis -Mixed Bag [ Mutiple Concepts Tested in One Question] Paper 4 IGCSE Chemistry Topic Questions

Question Paper:

The results of experiments on electrolysis using inert electrodes are given in the table.
Complete the table; the first line has been completed as an example.

electrolyte	change at negative electrode	change at positive electrode	change to electrolyte
molten lead(II) bromide	lead formed	bromine formed	used up
.......................................	potassium formed	iodine formed	used up
dilute aqueous sodium chloride	.......................................	.......................................	.......................................
aqueous copper(II) sulfate	.......................................	.......................................	.......................................
.......................................	hydrogen formed	bromine formed	potassium hydroxide formed

Mark Scheme:
- molten potassium iodide NOT aqueous [1]
- hydrogen [1]
- oxygen [1]
- water used up or solution becomes more concentrated or sodium chloride remains
- NOT no change
- If products are given as hydrogen, chlorine and sodium hydroxide then 2/3
- copper [1]
- oxygen (and water) [1]
- sulfuric acid accept hydrogen sulfate [1]
- aqueous or dilute or concentrated potassium bromide [1]
- accept correct formulae

4.1.8 Construct Ionic Half Equations Paper 4 IGCSE Chemistry Topic Questions

Q1: Electrolysis is carried out on aluminium oxide dissolved in molten cryolite.
Write the ionic half-equation for the reaction occurring at the negative electrode. [2]
Mark Scheme:
(ii) Al³⁺ + 3e^- → Al
M1 only Al³⁺ + (3) e^- on the left [1]
M2 equation fully correct [1]

4.1.9 Electroplating Paper 4 IGCSE Chemistry Topic Questions

Q1:

One of the methods used to prevent iron or steel from rusting is to electroplate it with another metal, such as tin. Complete the following.
The anode is made of ................................................. .
The cathode is made of ................................................. .
The electrolyte is a solution of ............................................[3] .

Marking Scheme:

anode

tin NOT impure tin [1]

cathode

iron or steel [1]

electrolyte

tin salt or tin ions as electrolyte

NOT oxide or hydroxide or carbonate [1]

Q1:
- A metal spoon is electroplated with copper.
- State what is used as:
  - the positive electrode (anode) ......................................................................................
  - the negative electrode (cathode) ...................................................................................
  - the electrolyte ...................................................................................................................
- [3]

Mark Scheme:
- Positive electrode (anode): copper (1)
- Negative electrode (cathode): spoon (1)
- Electrolyte: (aqueous or solution) of named copper salt (1)

4.2 Hydrogen-Oxygen Fuel Cells Paper 4 IGCSE Chemistry Topic Questions

Q1: Hydrogen–oxygen fuel cells can be used to produce electricity in vehicles.

(i) Write the symbol equation for the overall reaction in a hydrogen–oxygen fuel cell.
.............................................................................................................................................. [2]
(ii) State one advantage of using hydrogen–oxygen fuel cells instead of petrol in vehicle engines.
.............................................................................................................................................. [1]

Mark Scheme:

(i) 2H₂ + O₂ → 2H₂O

M1 all formulae [1]
M2 equation correct [1]

(ii) no carbon dioxide evolved; OR more efficient [1]

5.1.1 Endothermic / Exothermic Reactions Basics Paper 4 IGCSE Chemistry Topic Questions

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Q: State the meaning of the term endothermic. [1]

Mark scheme:
- Reaction which absorbs heat / absorbs thermal energy (from the surroundings). [1]

Solution

An endothermic reaction absorbs heat (thermal energy) from its surroundings.

(Accept either wording; do not award for statements like “temperature decreases” without mentioning heat absorbed.)

5.1.3 Enthalpy Change and Bond Energy Calculation Paper 4 IGCSE Chemistry Topic Questions

Q1: Chloroethene (CH₂=CHCl) can be manufactured from 1,2-dichloroethane (CH₂ClCH₂Cl).
The equation can be represented as shown:

    Cl      H
    |       |
H — C — C — H   →   H — C = C — H   +   H — Cl
    |       |               |
    H      Cl              Cl

Some bond energies are given:
- C—C: 350 kJ/mol
- C=C: 610 kJ/mol
- C—Cl: 340 kJ/mol
- C—H: 410 kJ/mol
- H—Cl: 430 kJ/mol
Use the bond energies in the table to calculate the energy change, in kJ/mol, of the reaction.
Use the following steps:
- Calculate the energy needed to break bonds.
- Calculate the energy released when bonds form.
- Calculate the energy change of the reaction.

Mark Scheme:
M1: 2670 (1)
M2: 2610 (1)
M3: (+) 60 (1)

6.1 Physical and Chemical Change — Paper 4 IGCSE Chemistry Topic Questions

Q: Substance Y undergoes physical and chemical changes.

Which two of the following are physical changes? Explain your answer.

A. Substance Y dissolves easily in water.
B. An aqueous solution of substance Y gives a white precipitate with acidified aqueous silver nitrate.
C. Substance Y melts at 801 °C.
D. Substance Y reacts with concentrated sulfuric acid.

[Click here and use Add Image button for Question Diagram]
Mark Scheme:
- A: Substance Y dissolves easily in water (1)
- C: Substance Y melts at 801 °C (1)
- The change can be reversed by altering the conditions (1)
[Click here and use Add Image button for Mark Scheme Table]

Solution

The two physical changes are:
• A: Substance Y dissolves easily in water.
• C: Substance Y melts at 801 °C.

These are physical changes because they can be reversed by altering the conditions — no new substance is formed in either case.

6.2 Effect of Changing the Concentration and Temperature of Solutions on the Rate of Reaction — Paper 4 IGCSE Chemistry Topic Questions

Q: Describe the effect of each of the following on the rate of reaction of dilute hydrochloric acid with calcium carbonate.

● The concentration of hydrochloric acid is decreased. All other conditions stay the same.

● The temperature is increased. All other conditions stay the same.

[2]
Mark Scheme:
- Lower concentration of acid: decreases in rate / reaction slower / lower rate / slows down (1)
- Higher temperature: increases in rate / reaction faster / higher rate / speeds up (1)

Solution

• When the concentration of hydrochloric acid is decreased, the rate of reaction decreases — the reaction becomes slower.

• When the temperature is increased, the rate of reaction increases — the reaction becomes faster.

6.2 Effect on the Rate of Reaction of Changing the Pressure of Gases — Paper 4 IGCSE Chemistry Topic Questions

Q: Ethene gas reacts with steam to form gaseous ethanol.

C₂H₄(g) + H₂O(g) ⇌ CH₃CH₂OH(g)

The reaction can reach a position of equilibrium. The forward reaction is exothermic.

(i) State and explain the effect of increasing the pressure on the position of equilibrium. All other conditions are unchanged. [2]

(ii) Increasing the pressure of a gas increases its concentration. State and explain the effect of increasing the pressure on the rate of the reaction. All other conditions are unchanged. [2]

[Click here and use Add Image button for Question Diagram]
Mark Scheme:
- (i) Moves right (1); fewer moles/molecules of gas on right (1)
- (ii) Reaction is faster because more collisions per second (1); particles/molecules closer together or more particles per unit volume (1)
[Click here and use Add Image button for Mark Scheme Table]

Solution

(i) Increasing the pressure shifts the equilibrium to the right, because there are fewer moles of gas on the right-hand side of the equation.

(ii) Increasing the pressure makes the reaction faster because the gas molecules are closer together, so there are more collisions per second and therefore a higher rate of reaction.

6.2 Effect on the Rate of Reaction of Changing the Surface Area of Solids — Paper 4 IGCSE Chemistry Topic Questions

Q: One of the factors which determine the reaction rate of solids is particle size.

(a) A mixture of finely powdered aluminium and air may explode when ignited. An explosion is a very fast exothermic reaction. This causes a large and sudden increase in temperature.

Explain each of the following in terms of collisions between reacting particles:
(i) Why is the reaction between finely powdered aluminium and air very fast? [2]
(ii) Explain why for most reactions the rate of reaction decreases with time. [2]
(iii) Suggest an explanation why the rate of reaction in an explosion could increase rather than decrease with time. [3]

(b) (i) Give another example of a substance other than a metal which, when finely powdered, might explode when ignited in air. [1]
(ii) Describe a simple test-tube reaction which shows the effect of particle size on the rate at which a solid reacts with a solution. [3]

[Click here and use Add Image button for Question Diagram]
Mark Scheme:
- (a)(i) Large/high surface area → high collision rate, more collisions between oxygen molecules and aluminium atoms (not faster collisions) (2)
- (a)(ii) Concentration of reactants decreases → fewer collisions (1)
- (a)(iii) Increase in temperature → molecules move faster/particles have more energy → higher collision rate → more successful collisions/more particles with enough energy to react (any 3 points) (3)
- (b)(i) Flour / wood dust / coal dust / carbon / sugar (1)
- (b)(ii) Example: marble chips with hydrochloric acid — smaller chips react faster because of larger surface area (3)
[Click here and use Add Image button for Mark Scheme Table]

Solution

(a)(i) Finely powdered aluminium has a large surface area, so there are many collisions per second between oxygen molecules and aluminium atoms, making the reaction very fast.

(a)(ii) For most reactions, the concentration of reactants decreases with time, so there are fewer collisions and the reaction rate slows down.

(a)(iii) In an explosion, the temperature rises sharply, particles gain more energy and move faster, collision frequency increases, and more particles have enough energy to react. This leads to the rate increasing rather than decreasing.

(b)(i) Substances such as flour, wood dust, coal dust, carbon or sugar can also explode when finely powdered and ignited in air.

(b)(ii) A simple test-tube reaction is the reaction of marble chips with hydrochloric acid. Smaller chips react faster because they have a larger surface area, leading to more frequent collisions with acid particles.

6.2 effect on the rate of reaction of adding or removing a catalyst, including enzymes — Paper 4 IGCSE Chemistry Topic Questions

Q: The rate of reaction of zinc powder with dilute sulfuric acid is found by measuring the increase in volume of hydrogen gas produced as time increases.

Describe the effect, if any, of each of the following on the rate of this reaction (all other conditions stay the same):

• The reaction is carried out with large pieces of zinc instead of zinc powder.

• The reaction is carried out using a catalyst.

• The reaction is carried out with dilute sulfuric acid of a lower concentration.

[3]
[Click here and use Add Image button for Question Diagram]
Mark Scheme:
- large pieces: (rate) decreases / reaction gets slower (1)
- catalyst: (rate) increases / reaction gets faster (1)
- lower concentration: (rate) decreases / reaction gets slower (1)
[Click here and use Add Image button for Mark Scheme Table]

Solution

• Using large pieces of zinc instead of powder makes the reaction slower — the rate decreases (smaller surface area).

• Using a catalyst makes the reaction faster — the rate increases (provides an alternative pathway with lower activation energy).

• Using acid of lower concentration makes the reaction slower — the rate decreases (fewer effective collisions per second).

6.2 Investigating Rate of Reaction Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

6.3.1 Reversible Reactions Paper 4 IGCSE Chemistry Topic Questions

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Q: State what is meant by the term equilibrium. [2]

Mark Scheme:
- M1: The rate of the forward reaction equals the rate of the reverse reaction. [1]
- M2: The concentrations of reactants and products remain constant. [1]

Solution

Chemical equilibrium is the state in a reversible reaction where the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products stay constant (though not necessarily equal).

6.3.2 Effect of Temperature & Pressure on Equilibrium (Exothermic Forward) — Paper 4 IGCSE Chemistry Topic Questions

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Q: The forward reaction is exothermic.
State the effect, if any, on the position of equilibrium when the following changes are made. Explain your answers.
- (i) temperature is reduced
- (ii) pressure is reduced

Mark Scheme:
- Reduced temperature:
- M1: (Position of) equilibrium moves to the right-hand side. (1)
- M2: Because the forward reaction is exothermic. (1)
- Reduced pressure:
- M3: (Position of) equilibrium moves to the left-hand side. (1)
- M4: There are more gaseous moles on the left-hand side. (1)

Solution

(i) Temperature reduced: The equilibrium shifts to the right (products) to oppose the decrease in temperature by favouring the exothermic (heat-releasing) direction.

(ii) Pressure reduced: The equilibrium shifts to the left because that side has more moles of gas, so moving left increases pressure and opposes the change.

6.3.2 Effect of Concentration on Equilibrium in a Reversible Reaction Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

6.3.2 Effect of Catalyst on Equilibrium in a Reversible Reaction Paper 4 IGCSE Chemistry Topic Questions

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Q: Sulfur dioxide is used to make sulfur trioxide in the Contact Process.
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) (forward reaction is exothermic).
Conditions used: 450 °C; 2 atm; catalyst: vanadium(V) oxide.

Explain, mentioning both position of equilibrium and rate, why these conditions give the most economic yield. [4]

Mark Scheme:
- M1: Lower temperatures favour the exothermic forward reaction / increase equilibrium yield of SO₃. [1]
- M2: But too low a temperature gives a very slow rate; 450 °C is a compromise giving a reasonable rate. [1]
- M3: Catalyst V₂O₅ increases rate (at the same temperature) / does not change equilibrium position or yield. [1]
- M4: Fewer moles of gas on the right (3 → 2), so higher pressure would increase yield/rate, but 2 atm is chosen as yield is high enough and higher pressure is costly. [1]

Solution

Because the forward reaction is exothermic, a lower temperature pushes the equilibrium to the right to give more SO₃. However, too low a temperature makes the reaction slow, so a compromise 450 °C is used. The V₂O₅ catalyst speeds the reaction but does not change the equilibrium yield. There are fewer gas molecules on the right (3 → 2), so high pressure would raise yield, but the improvement is modest; therefore a low/medium pressure (~2 atm) is used as a cost-effective compromise giving a good economic yield at acceptable rate.

6.3.2 Effect of water and heat on the Reversible Reaction of Copper Sulfate and Cobalt Chloride Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe how cobalt chloride paper can be used to test for the presence of water. [2]

..........................................................................................................................................

..........................................................................................................................................
Mark Scheme (Q1):
- (changes from) blue (1)
- (to) pink (1)

Solution Q1

Cobalt chloride paper changes from blue to pink in the presence of water.

Q2: Anhydrous copper(II) sulfate is used to test for water. State the colour change in this test. [2]

from .................................................................................................

to ....................................................................................................
Mark Scheme (Q2):
- (from) white (1)
- (to) blue (1)

Solution Q2

Anhydrous copper(II) sulfate changes from white to blue in the presence of water.

6.3.2 Haber's Process Paper 4 IGCSE Chemistry Topic Questions

Q1: Nitrogen reacts with hydrogen to form ammonia, NH₃, in the Haber process.
- State the essential conditions in the Haber process.
- Write an equation for the chemical reaction.
- ....................................................................................................................................................
  ....................................................................................................................................................
  ....................................................................................................................................................
  ....................................................................................................................................................
  ....................................................................................................................................................
- [4]
Mark Scheme:
- 450 °C (1)
- 200 atmospheres (1)
- Iron (catalyst) (1)
- N₂ + 3H₂ ⇌ 2NH₃ (1)

6.3.2 Contact Process Paper 4 IGCSE Chemistry Topic Questions

Q1: Sulfuric acid is manufactured by an industrial process. Sulfur is obtained from sulfur-containing metal ores.
The sulfur in the metal ore is converted to sulfur dioxide which is then oxidised to sulfur trioxide as shown.
2SO₂(g) + O₂(g) → 2SO₃(g)
- (a) Name a metal ore which contains sulfur.
  .............................................................................................................................................. [1]
- (b) Describe the process which converts metal ores to sulfur dioxide.
  .............................................................................................................................................. [1]
- (c) Name the industrial process used to manufacture sulfuric acid.
  .............................................................................................................................................. [1]
- (d) The reaction that produces sulfur trioxide is an equilibrium. The forward reaction is exothermic.
  - (i) State the temperature and pressure used to make sulfur trioxide.
    temperature = .............................. °C
    pressure = .............................. atm [2]
  - (ii) Name the catalyst used.
    ....................................................................................................................................... [1]
  - (iii) Describe two features of an equilibrium.
    1 ..........................................................................................................................................
    2 .......................................................................................................................................... [2]
  - (iv) State the effect, if any, on the position of equilibrium when the following changes are made. Explain your answers.
    - temperature is increased
      ....................................................................................................
      .............................................................................................................................................
    - pressure is increased
      .......................................................................................................
      ............................................................................................................................................. [4]
- Explain, in terms of particles, what happens to the rate of reaction when the temperature is increased.
  .............................................................................................................................................
  .............................................................................................................................................
  .............................................................................................................................................
  .............................................................................................................................................
  ....................................................................................................................................... [3]

Mark Scheme:
- (a) zinc blende [1]
- (b) strong heating in air / roasting in air [1]
- (c) contact [1]
- (d)(i)
  - M1 450 °C (1)
  - M2 1–2 atm (1)
  [2]
- (d)(ii) vanadium(V) oxide [1]
- (d)(iii)
  - M1 the rate of forward reaction equals (the rate of the) reverse reaction (1)
  - M2 concentrations of reactants and products are constant (1)
  [2]
- (d)(iv)
  - Increased temperature:
    - M1 (position of) equilibrium moves to left-hand side (1)
    - M2 reaction is exothermic (1)
  - Increased pressure:
    - M3 (position of) equilibrium moves to right-hand side (1)
    - M4 more (gaseous) moles/molecules on left-hand side (1)
  [4]

6.3.2 Redox Reaction Paper 4 IGCSE Chemistry Topic Questions

Q1: Iron is extracted from its ore, hematite, in the blast furnace.
Describe the reactions involved in this extraction. Include one equation for a redox reaction and one for an acid/base reaction.
[5]

Mark Scheme:
- One redox equation from: [1]
  - Fe₂O₃ + 3CO → 2Fe + 3CO₂
  - 2Fe₂O₃ + 3C → 4Fe + 3CO₂
  - Fe₂O₃ + 3C → 2Fe + 3CO
  - C + O₂ → CO₂
  - CO₂ + C → 2CO
- One acid/base equation: [1]
  - CaO + SiO₂ → CaSiO₃
  - CaCO₃ + SiO₂ → CaSiO₃ + CO₂
- Any three additional equations or comments from: [3]
  - carbon burns or reacts to form carbon dioxide;
  - this reaction is exothermic or produces heat;
  - carbon dioxide is reduced to carbon monoxide;
  - carbon monoxide reduces hematite to iron;
  - carbon reduces hematite to iron;
  - limestone removes silica to form slag;
  - limestone decomposes;

6.3.2 Oxidation Reduction Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

6.3.2 Oxidising and Reducing Agent Paper 4 IGCSE Chemistry Topic Questions

Q1: The reactivity series shows the metals in order of reactivity.
- (a) The reactivity series can be established using displacement reactions.
  - A piece of zinc is added to aqueous lead nitrate. The zinc becomes coated with a black deposit of lead.
  - Zn + Pb²⁺ → Zn²⁺ + Pb
  - Zinc is more reactive than lead.
- The reactivity series can be written as a list of ionic equations:
  - ...... → ...... + ...... (most reactive metal: the best reductant)
  - Zn → Zn²⁺ + 2e
  - Fe → Fe²⁺ + 2e
  - Pb → Pb²⁺ + 2e
  - Cu → Cu²⁺ + 2e
  - Ag → Ag⁺ + e^–
- (i) Explain why the positive ions are likely to be oxidants (oxidising agents).
  - ..............................................................................................................................
  - [1]
- (ii) Deduce which ion is the best oxidant (oxidising agent).
  - ..............................................................................................................................
  - [1]
- (iii) Which ion(s) in the list can oxidise lead metal?
  - ..............................................................................................................................
  - [1]
Mark Scheme:
- (i) Because they can accept or gain electrons / change into atoms or can be reduced [1]
- (ii) Ag⁺ or silver [1] (charge not essential but if given, it must be correct)
- (iii) Ag⁺ and Cu²⁺ or silver and copper [1]

7.1.1 Effect of Indicators [ litmus, thymolphthalein and methyl orange on Acids Paper 4 IGCSE Chemistry Topic Questions

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Q1:
- (i) Describe how universal indicator can be used to find the pH of an acidic solution.
- ....................................................................................................................................................
- ....................................................................................................................................................
- .................................................................................................................................................... [2]

Mark Scheme:
- M1: Add indicator (paper) to acid / solution [1]
- M2: Compare colour with indicator colour chart / (pH) colour chart [1]

Solution

Add universal indicator (or indicator paper) to the acidic solution.
[OR] Dip universal indicator paper into the solution.

Compare the colour change of the indicator with the colours shown on the pH chart.
The colour will indicate the pH value of the acidic solution.

Q1: A student determines the concentration of a solution of dilute sulfuric acid, H₂SO₄, by titration with aqueous sodium hydroxide, NaOH.
- Step 1: 25.0 cm³ of 0.200 mol/dm³ NaOH is transferred into a conical flask.
- Step 2: Three drops of methyl orange indicator are added to the conical flask.
- Step 3: A burette is filled with H₂SO₄.
- Step 4: The acid in the burette is added to the conical flask until the indicator changes colour. The volume of acid is recorded. This process is known as titration.
- Step 5: The titration is repeated several times until a suitable number of results is obtained.

Mark Scheme:
- Indicator changes colour: yellow to orange [1]

Solution

During the titration, the methyl orange indicator changes colour from yellow to orange as the acid is added to the sodium hydroxide solution.

7.1.1 Reaction of Acids with metals, base, carbonates and ammonium salts Paper 4 IGCSE Chemistry Topic Questions

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Q1: Complete the word equations for the reactions of ethanoic acid:
- calcium + ethanoic acid → ................................................................. + .................................................................
- ....................................................... + ethanoic acid → zinc ethanoate + water
- .................................................................................................................................................... [2]

Mark Scheme:
- (i): calcium ethanoate + hydrogen [1]
- (ii): zinc oxide or hydroxide [1]

Solution

(i) Calcium reacts with ethanoic acid to form **calcium ethanoate** and **hydrogen gas**.
Word Equation: calcium + ethanoic acid → calcium ethanoate + hydrogen

(ii) Zinc oxide or zinc hydroxide reacts with ethanoic acid to form **zinc ethanoate** and **water**.
Word Equation: zinc oxide or zinc hydroxide + ethanoic acid → zinc ethanoate + water.

Q2: Write a chemical equation for the reaction between magnesium and dilute hydrochloric acid.
- .................................................................................................................................................... [2]

Mark Scheme:
- Mg + 2HCl → MgCl₂ + H₂ [2]

Solution

The balanced chemical equation for the reaction between **magnesium (Mg)** and **dilute hydrochloric acid (HCl)** is:

Mg + 2HCl → MgCl₂ + H₂

- Magnesium reacts with hydrochloric acid to produce **magnesium chloride (MgCl₂)** and **hydrogen gas (H₂)**.
- Two molecules of hydrochloric acid are needed to completely react with one atom of magnesium to balance the equation.

Question:

Dilute sulfuric acid reacts with bases, metals, and carbonates.
Write chemical equations for the reaction of dilute sulfuric acid with each of the following:

(i) magnesium hydroxide
(ii) zinc
(iii) sodium carbonate

Mark Scheme:

(i) Mg(OH)₂ + H₂SO₄ → MgSO₄ + 2H₂O
(ii) Zn + H₂SO₄ → ZnSO₄ + H₂
(iii) Na₂CO₃ + H₂SO₄ → Na₂SO₄ + CO₂ + H₂O

Solution:

(i) Magnesium hydroxide reacts with sulfuric acid to form magnesium sulfate and water:

Mg(OH)₂ + H₂SO₄ → MgSO₄ + 2H₂O

(ii) Zinc reacts with sulfuric acid to form zinc sulfate and hydrogen gas:

Zn + H₂SO₄ → ZnSO₄ + H₂

(iii) Sodium carbonate reacts with sulfuric acid to form sodium sulfate, carbon dioxide, and water:

Na₂CO₃ + H₂SO₄ → Na₂SO₄ + CO₂ + H₂O

Each reaction involves sulfuric acid reacting with a base, a metal, or a carbonate to produce respective products. Balanced equations ensure that all atoms are accounted for.

7.1.1 Effect of Indicators [ litmus, thymolphthalein and methyl orange on Alkalis Paper 4 IGCSE Chemistry Topic Questions

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Q1:
- (i) Describe how universal indicator can be used to find the pH of an acidic solution.
- ....................................................................................................................................................
- ....................................................................................................................................................
- .................................................................................................................................................... [2]

Mark Scheme:
- M1: Add indicator (paper) to acid / solution [1]
- M2: Compare colour with indicator colour chart / (pH) colour chart [1]

Solution

7.1.1 Ammonia Preparation — Balance the Equation (IGCSE Chemistry)

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Q: Ammonia is made in the laboratory by heating ammonium chloride with calcium hydroxide.
Balance the chemical equation for the reaction.
…..NH₄Cl + Ca(OH)₂ → …..NH₃ + CaCl₂ + …..H₂O [1]
Mark scheme:
- 2NH₄Cl + Ca(OH)₂ → 2NH₃ + CaCl₂ + 2H₂O [1]

Solution & Explanation

This is a reaction of an ammonium salt with a strong base. Hydroxide ions remove a proton from ammonium: NH₄⁺ + OH⁻ → NH₃ + H₂O.

With calcium hydroxide: 2NH₄⁺ + Ca(OH)₂ → 2NH₃ + 2H₂O + Ca²⁺. The Ca²⁺ combines with 2Cl⁻ (from 2NH₄Cl) to form CaCl₂.

Balancing steps:
• Put 1 Ca on each side ⇒ CaCl₂ needs 2 Cl, so use 2NH₄Cl.
• That gives 2 N, so make 2NH₃ on the right.
• Count H and O: left has 8 (from 2NH₄) + 2 (from Ca(OH)₂) = 10 H. Right: 2NH₃ has 6 H, so need 2H₂O (4 H) to total 10.

Final balanced equation: 2NH₄Cl + Ca(OH)₂ → 2NH₃ + CaCl₂ + 2H₂O.

7.1.1 Strong and Weak Acids Paper 4 IGCSE Chemistry Topic Questions

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Q: Sulfuric acid has many uses and is a strong acid.
(a)(i) Define the term acid. ........................................................................................................ [1]
(a)(ii) Define the term strong acid. .................................................................................................... [1]
Mark scheme:
- (a)(i) proton donor (donates H⁺). [1]
- (a)(ii) completely dissociated in aqueous solution (fully ionises to give H⁺/H₃O⁺). [1]

Solution & Explanation

By the Brønsted–Lowry definition, an acid is a proton (H⁺) donor.

A strong acid is one that fully dissociates in water. For sulfuric acid: H₂SO₄(aq) → 2H⁺(aq) + SO₄²⁻(aq) (in the first step it dissociates completely), so the solution contains (nearly) only ions and no undissociated acid molecules.

7.1.1 Strong and Weak Bases Paper 4 IGCSE Chemistry Topic Questions

Q1:
- (i) In terms of proton transfer, explain what is meant by the term weak base.
- ....................................................................................................................................................
- .................................................................................................................................................... [2]
- (ii) Given aqueous solutions of both bases, describe how you could show that sodium hydroxide is the stronger base. How could you ensure a ‘fair’ comparison between the two solutions?
- ....................................................................................................................................................
- ....................................................................................................................................................
- ....................................................................................................................................................
- .................................................................................................................................................... [3]

Mark Scheme:
- (i):
  - M1: Proton acceptor
  - M2: Does not accept protons readily OR Less able to accept protons (than strong bases)
- (ii):
  - M1: Use the same concentration of both bases
  - M2: Measure their pH
  - M3: The solution with the higher pH is the stronger base

Solution

(i) A weak base is a proton acceptor that does not accept protons readily
[OR] It is less able to accept protons compared to a strong base.

(ii) To compare the two bases:
• Use the same concentration of both bases.
• Measure their pH using a pH meter, universal indicator, or pH paper.
• The base with the higher pH value is the stronger base.

This ensures a fair comparison as both bases are tested under the same conditions.

7.1.1 Comparing hydrogen ion concentration, neutrality, relative acidity and relative alkalinity in terms of colour and pH using universal indicator paper Paper 4 IGCSE Chemistry Topic Questions

Q: The bubbles in fizzy drinks are bubbles of carbon dioxide. The carbon dioxide is dissolved in the drink under pressure. When a bottle of fizzy drink is opened the gas escapes and eventually the drink goes flat. The gas is lost more quickly if the fizzy drink is heated.

(a) How could the acidity of the fizzy drink be checked? [1]

Mark Scheme:
- Use Universal/pH indicator/pH meter (1)
- Ignore: litmus/indicator

Solution

The acidity of the fizzy drink can be checked using a Universal indicator or a pH meter.

7.1.1 Acidic Basic and Amphoteric Oxides Paper 4 IGCSE Chemistry Topic Questions

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Q: Amphoteric oxides and neutral oxides are different from each other.
- (i) What is meant by the term amphoteric oxide? ............................................................... [1]
- (ii) What is meant by the term neutral oxide? .................................................................. [1]
Mark scheme:
- (i) An amphoteric oxide reacts with acids AND with bases. [1]
- (ii) A neutral oxide does not react with acids or with bases. [1]

7.1.1 Neutralisation Reactions Paper 4 IGCSE Chemistry Topic Questions

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Q: Define neutralisation and write the net ionic equation for the reaction between an acid and an alkali. [2]

Mark scheme:
- M1: Reaction in which H⁺ from an acid reacts with OH⁻ from an alkali/base to form water. [1]
- M2: Net ionic: H⁺ + OH⁻ → H₂O (state symbols optional). [1]

Solution

Definition: Neutralisation is when hydrogen ions from an acid react with hydroxide ions from an alkali to form water.
Net ionic equation: H⁺(aq) + OH⁻(aq) → H₂O(l)

7.1.1 Water of Crystallisation Paper 4 IGCSE Chemistry Topic Questions

Q: Define water of crystallisation. [1]

Mark Scheme:
- Water of crystallisation is a fixed number of water molecules chemically bound within the crystal structure of a salt (1)

Solution

Water of crystallisation refers to the fixed number of water molecules that are chemically bound within the crystal lattice of a salt.

7.1.1 Making Pure, Dry Salt By Precipitation Method Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe how you would make a pure, dry sample of barium carbonate by precipitation.

Include:
the names of the starting materials
full practical details
a chemical equation.

Mark Scheme:

M1: Mix sodium carbonate AND barium nitrate/barium chloride
M2: In solution/aqueous/dissolved in water
M3: Filter/centrifuge (barium carbonate)
M4: Wash (residue) AND dry/description of washing and drying
M5: Ba(NO₃)₂ + Na₂CO₃ → BaCO₃ + 2NaNO₃
[OR] BaCl₂ + Na₂CO₃ → BaCO₃ + 2NaCl

Solution

1. Starting materials: Sodium carbonate (Na₂CO₃) and barium nitrate (Ba(NO₃)₂) [OR] barium chloride (BaCl₂).
2. Full practical details:

Mix solutions of sodium carbonate and barium nitrate/barium chloride. A white precipitate of barium carbonate forms.
Filter the mixture to separate the solid barium carbonate.
Wash the precipitate with distilled water to remove impurities.
Dry the solid barium carbonate to obtain a pure, dry sample.

3. Chemical Equation:

Ba(NO₃)₂ + Na₂CO₃ → BaCO₃ + 2NaNO₃
[OR] BaCl₂ + Na₂CO₃ → BaCO₃ + 2NaCl

8.1 Periodic Table Basics Paper 4 IGCSE Chemistry Topic Questions

Q: The names of the elements of Period 2 of the Periodic Table are shown:

lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon

Answer the following questions about these elements. Each element may be used once, more than once or not at all.

(a) is a product of photosynthesis [1]
(b) has an oxide found in clean, dry air [1]
(c) forms a basic oxide with the formula X₂O [1]
(d) is a main component of fertilisers used to improve crop growth [1]
(e) has the highest rate of diffusion at room temperature [1]
(f) produces a red flame in a flame test [1]
(g) has only 5 electrons in each of its atoms [1]
(h) has an oxide responsible for acid rain [1]

Mark Scheme:
- (a) oxygen (1)
- (b) carbon (1)
- (c) lithium (1)
- (d) nitrogen (1)
- (e) neon (1)
- (f) lithium (1)
- (g) boron (1)
- (h) nitrogen (1)

Solution

(a) Oxygen
(b) Carbon
(c) Lithium
(d) Nitrogen
(e) Neon
(f) Lithium
(g) Boron
(h) Nitrogen

8.2 Group 1 Elements Paper 4 IGCSE Chemistry Topic Questions

Q1:
- (a) Group I elements react with cold water to form alkaline solutions.
- (i) Place the Group I elements caesium, lithium, potassium, rubidium, and sodium in their order of reactivity with water.
- Put the most reactive element first.
- most reactive → ____________________ → ____________________ → ____________________ → ____________________ → least reactive
- [1]
- (ii) Name the alkaline solution formed when caesium reacts with cold water.
- ...........................................................................................................................
- [1]
- (b) Group I elements have lower melting points than transition elements.
- Describe one other difference in the physical properties of Group I elements and transition elements.
- ...........................................................................................................................
- [1]

Mark Scheme:
- (a)(i) from left to right: caesium → rubidium → potassium → sodium → lithium [1]
- (a)(ii) caesium hydroxide [1]
- (b)
  - Group I element is less strong / not strong ORA
  - OR Group I element has low(er) density ORA
  - OR Group I element is soft(er) ORA

Solution

(a)(i) Caesium → Rubidium → Potassium → Sodium → Lithium
(a)(ii) Caesium hydroxide
(b) Group I element is less strong ORA.
OR Group I element has lower density ORA.
OR Group I element is softer ORA.

8.3.1 Group 7 Elements Paper 4 IGCSE Chemistry Topic Questions

Q1:
- (c) Group VII elements are known as the halogens.
- Astatine is below iodine in Group VII.
- Predict the physical state of astatine at room temperature and pressure.
- .................................................................................................................... [1]
- (d) Some Group VII elements react with aqueous solutions containing halide ions.
- When aqueous chlorine is added to aqueous potassium bromide a reaction occurs.
- The ionic half-equations for the reaction are shown:
- Cl₂(aq) + 2e^– → 2Cl^–(aq)
  2Br^–(aq) → Br₂(aq) + 2e^–
- (i) Describe the colour change of the solution.
- Original colour of potassium bromide solution: ..................................................
- Final colour of reaction mixture: ................................................................. [2]

Mark Scheme:
- (c) solid [1]
- (d)(i)
  - Original colour: colourless (1)
  - Final colour: orange / brown / yellow (1)

Solution

(c) Solid
(d)(i) Original colour of potassium bromide solution: colourless
Final colour of reaction mixture: orange / brown / yellow

8.3.2 Group 7 Reactions Paper 4 IGCSE Chemistry Topic Questions

Q: The halogens are the elements in Group VII of the Periodic Table.
- (a) Predict the physical state and colour of astatine at room temperature and pressure. [2]
- (b) When chlorine reacts with aqueous potassium bromide a displacement reaction occurs.
- (i) Describe the colour change of the solution: from ______ to ______. [2]
- (ii) Write a chemical equation for this reaction. [2]

Mark Scheme:
- (a) M1 solid (1) M2 black (1)
- (b)(i) M1 colourless (1) M2 to brown / orange / yellow (1)
- (b)(ii) Accept either full or ionic equation:
  - Cl₂ + 2KBr → 2KCl + Br₂ or
  - Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂
  M1 all formulae correct (1); M2 equation balanced (1)

Solution

(a) Physical state: solid | Colour: black

(b)(i) Colour change: from colourless to brown / orange / yellow (bromine formed).

(b)(ii) Displacement equation (either form acceptable):
Cl₂ + 2KBr → 2KCl + Br₂
or Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂

8.4 Transition Elements Paper 4 IGCSE Chemistry Topic Questions

Q1:
- (a) State two other chemical properties of transition elements which make them different from Group I elements.
- 1 ................................................................................................................................................
- 2 ................................................................................................................................................
- [2]

Mark Scheme:
- Form coloured compounds or ions. [1]
- Act as catalysts. [1]

Solution

Form coloured compounds or ions.
Act as catalysts.

8.5 Noble Gases Paper 4 IGCSE Chemistry Topic Questions

Q: Helium, neon and argon are noble gases.
- (i) Explain, in terms of the electronic structure, why neon is unreactive. [1]
- (ii) State one use of argon. [1]

Mark Scheme:
- (i) has complete outer (electron) shell / full outer shell / outer shell cannot gain or lose electron(s) (1)
- (ii) lamps / provides an inert atmosphere (e.g. in metal extraction or welding) (1)

Solution

(i) Neon is unreactive because it has a full outer electron shell, so it does not gain or lose electrons.

(ii) One use of argon: in lamps / to provide an inert atmosphere (e.g. during welding or metal extraction).

7.1.1 REaction of Acids with metals, base, carbonates and ammonium salts Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

7.1.1 Effect of Indicators [ litmus, thymolphthalein and methyl orange on Alkalis Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

7.1.1 Reaction of Base with Acid and Ammonium Salts Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

7.1.1 Strong and Weak Acids Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

7.1.1 Comparing hydrogen ion concentration, neutrality, relative acidity and relative alkalinity in terms of colour and pH using universal indicator paper Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

7.1.1 Neutralisation Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

7.1.1 Acidic Basic and Amphoteric Oxides Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

7.1.1 Neutralisation Reactions Paper 4 IGCSE Chemistry Topic Questions

Q1: Construct the equation for the complete neutralisation of sulfuric acid by potassium hydroxide. [1]

Mark Scheme:
- 2KOH + H₂SO₄ → K₂SO₄ + 2H₂O (1)

Solution

Balanced neutralisation equation:
2KOH + H₂SO₄ → K₂SO₄ + 2H₂O

Q2: A farmer adds excess calcium hydroxide to react with hydrogen ions in acidic soils. Write an ionic equation to show the neutralisation of hydrogen ions by solid calcium hydroxide. [1]

Mark Scheme:
- Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O (1)
- ALLOW: Ca²⁺ + 2OH^- + 2H⁺ → Ca²⁺ + 2H₂O (1)
- ALLOW: OH^- + H⁺ → H₂O (or multiples)

Solution

Ionic neutralisation equation:
Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O

7.1.1 Neutralisation Reactions Paper 4 IGCSE Chemistry Topic Questions

Q1: Construct the equation for the complete neutralisation of sulfuric acid by potassium hydroxide. [1]

Mark Scheme:
- 2KOH + H₂SO₄ → K₂SO₄ + 2H₂O (1)

Solution

Balanced neutralisation equation:
2KOH + H₂SO₄ → K₂SO₄ + 2H₂O

Q2: A farmer adds excess calcium hydroxide to react with hydrogen ions in acidic soils. Write an ionic equation to show the neutralisation of hydrogen ions by solid calcium hydroxide. [1]

Mark Scheme:
- Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O (1)
- ALLOW: Ca²⁺ + 2OH^- + 2H⁺ → Ca²⁺ + 2H₂O (1)
- ALLOW: OH^- + H⁺ → H₂O (or multiples)

Solution

Ionic neutralisation equation:
Ca(OH)₂ + 2H⁺ → Ca²⁺ + 2H₂O

8.1 Periodic Table Basics Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

8.2 Group 1 Elements Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

8.3.1 Group 7 Elements Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

8.3.2 Group 7 Reactions Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

8.4 Transition Elements Paper 4 IGCSE Chemistry Topic Questions

Co has high melting point / boiling point ORA for Li
Co has high density ORA for Li
Co has catalytic activity ORA for Li
Co forms coloured compounds ORA for Li
Co compounds have variable oxidation states / form ions with different charges ORA for Li
Co is hard / Co is strong ORA for Li
Co less reactive ORA for Li / Li reacts rapidly with water / Co does not react with water / Co reacts slowly with water
Co is magnetic ORA for Li

8.5 Noble Gases Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

9.1 Properties of Metals Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

9.2.1 Uses of Metals [ Copper and Aluminium ] Paper 4 IGCSE Chemistry Topic Questions

Q: Which uses of the metals shown are correct? Choose A, B, C or D. [1]

Proposed uses
Option	aluminium	stainless steel
A	aircraft bodies	car bodies
B	car bodies	aircraft bodies
C	chemical plant	food containers
D	food containers	cutlery

Mark Scheme:
- Answer: D (1)

Solution

Correct option: D
• Aluminium → food containers: low density and a protective oxide layer make Al light, non-toxic and corrosion-resistant—ideal for cans/foil.
• Stainless steel → cutlery: hard and highly corrosion-resistant, so it does not rust or stain with foods.

Why A–C are not correct:
A: stainless steel is heavy for car bodies; aircraft need very low mass (use aluminium).
B: stainless steel for aircraft is too heavy; aluminium can be used in some car parts but not typically over mild steel.
C: aluminium is attacked by many chemicals; chemical plant commonly uses stainless steel for better corrosion resistance.

9.3 Alloys Paper 4 IGCSE Chemistry Topic Questions

Q: Metals are often used in the form of alloys.
- (i) State the meaning of the term alloy. [1]
- (ii) Explain in terms of their properties why alloys are used instead of pure metals. [1]
- (iii) Stainless steel is an alloy. Give one use of stainless steel. [1]

Mark Scheme:
- (i) mixture of metal with another element (1)
- (ii) (alloy is) hard(er) / (more) resistant to corrosion / strong(er) (1)
- (iii) cutlery / chemical plant / surgical equipment (1)

Solution

(i) An alloy is a mixture of a metal with another element (often another metal).

(ii) Alloys are used instead of pure metals because they are typically harder, stronger and/or more resistant to corrosion.

(iii) One use of stainless steel: cutlery (accept: chemical plant equipment or surgical equipment).

9.4 Reactivity Series Paper 4 IGCSE Chemistry Topic Questions

Q1: The reactivity series shows the metals in order of reactivity.
- (a) The reactivity series can be established using displacement reactions.
  - A piece of zinc is added to aqueous lead nitrate. The zinc becomes coated with a black deposit of lead.
  - Zn + Pb²⁺ → Zn²⁺ + Pb
  - Zinc is more reactive than lead.
- The reactivity series can be written as a list of ionic equations:
  - Zn → Zn²⁺ + 2e
  - Fe → Fe²⁺ + 2e
  - Pb → Pb²⁺ + 2e
  - Cu → Cu²⁺ + 2e
  - Ag → Ag⁺ + e
- (i) In the space at the top of the list, write an ionic equation for a metal which is more reactive than zinc.
  - [1]
- (ii) Write an ionic equation for the reaction between aqueous silver(I) nitrate and zinc.
  - ..............................................................................................................................
  - [2]
Mark Scheme:
- (a)
  - (i) Any metal above zinc
  - Mg → Mg²⁺ + 2e^– [1]
  - (ii) Zn + 2Ag⁺ → Zn²⁺ + 2Ag [2]

9.5.1 Corrosion of Iron Paper 4 IGCSE Chemistry Topic Questions

Q: Rust contains compounds of iron.
State two conditions needed for iron to rust. [2]

Mark Scheme:
- M1: water
- M2: oxygen / air

Solution

Iron rusts only when water and oxygen (air) are both present.

9.5.2 Barrier Methods and Sacrificial Coating Paper 4 IGCSE Chemistry Topic Questions

Q(d): Steel consists mainly of iron. Iron forms rust when it reacts with water and oxygen.
Magnesium blocks can be attached to the bottom of steel boats. The magnesium does not completely cover the steel.

(i) Explain how the magnesium blocks prevent iron from rusting. [2]
(ii) Explain why replacing the magnesium blocks with copper blocks will not prevent the bottom of the boat from rusting. [1]

Mark Scheme:
- (i) Magnesium is more reactive than iron/steel (ORA).
  Iron is not oxidised / iron does not lose electrons.
  OR magnesium loses electrons more easily than iron (ORA).
  OR magnesium is oxidised/reacts with oxygen/corrodes more easily than iron (ORA). [2]
- (ii) Copper is less reactive than iron / copper is lower in the reactivity series than iron (ORA). [1]

Solution

(i) Magnesium is more reactive than iron. It loses electrons and oxidises more easily, so it corrodes in preference to iron. This prevents the iron in the steel from rusting.

(ii) Copper is less reactive than iron. If copper blocks were used, the iron would still corrode since copper cannot act as a sacrificial metal.

9.6.1 Metal Extraction Basics Paper 4 IGCSE Chemistry Topic Questions

Q: Aluminium is extracted from aluminium oxide by electrolysis.
Explain why aluminium is extracted by electrolysis and not by reduction with carbon. .......................................................................................................................................................................................... [1]

Mark Scheme:
- Aluminium is too reactive / aluminium is above carbon in the reactivity series. [1]

Solution

Aluminium is more reactive than carbon (it is above carbon in the reactivity series), so carbon cannot reduce aluminium oxide; therefore electrolysis is required.

9.6.1 Iron Extraction Paper 4 IGCSE Chemistry Topic Questions

Q(a): This question is about zinc and its compounds.

Zinc is extracted from its ore which is mainly zinc sulfide, ZnS. The steps for this extraction are shown.

Step 1: Zinc sulfide is converted into zinc oxide.
Step 2: The zinc oxide is then reduced to zinc in a furnace. The zinc formed becomes a gas.
Step 3: The zinc gas is cooled to form molten zinc.

(i) Name the ore of zinc, which is mainly zinc sulfide. [1]
(ii) Describe how zinc sulfide is converted into zinc oxide in step 1. [1]
(iii) Name the reducing agent used in step 2. [1]
(iv) Explain why the zinc forms a gas in step 2 inside the furnace. [1]
(v) State the name of the physical change occurring when zinc gas is converted into molten zinc. [1]

Mark Scheme:
- (i) zinc blende (1)
- (ii) heat zinc sulfide strongly in air / roast in air (1)
- (iii) carbon or carbon monoxide (1)
- (iv) temperature in the furnace is above the boiling point of zinc OR boiling point of zinc is below furnace temperature (1)
- (v) condensation / condensing / condense (1)

Solution

(i) The ore of zinc is zinc blende.

(ii) Zinc sulfide is converted into zinc oxide by heating strongly in air (roasting).

(iii) The reducing agent in step 2 is carbon or carbon monoxide.

(iv) Zinc forms a gas in the furnace because the temperature is higher than zinc’s boiling point.

(v) When zinc gas cools to molten zinc, the physical change is condensation.

9.6.1 Aluminium Extraction Paper 4 IGCSE Chemistry Topic Questions

Q1: Aluminium is extracted from its ore by electrolysis.

(a) Name the ore of aluminium which consists mainly of aluminium oxide.
- ..............................................................................................................................................
- [1]
(b) State what is meant by the term electrolysis.
- ....................................................................................................................................................
- ..............................................................................................................................................
- [2]
(c) Electrolysis is carried out on aluminium oxide dissolved in molten cryolite.
- (i) Give two reasons why the electrolysis is carried out on aluminium oxide dissolved in molten cryolite instead of electrolysing molten aluminium oxide only.
  - 1. ..........................................................................................................................................
  - 2. ..........................................................................................................................................
  - [2]
- (ii) Write the ionic half-equation for the reaction occurring at the negative electrode.
  - .......................................................................................................................................
  - [2]
- (iii) The positive electrodes are made of carbon. Explain why the positive carbon electrodes are replaced regularly.
  - .............................................................................................................................................
  - .......................................................................................................................................
  - [2]

Mark Scheme:

(a): Bauxite [1]
(b):
- M1: Breakdown by (the passage of) electricity [1]
- M2: Of an ionic compound in molten or aqueous (state) [1]
(c):
- (i)
  - M1: Improves conductivity of the electrolyte / makes the electrolyte a better conductor [1]
  - M2: Lowers operating temperature [1]
- (ii)
  - M1: Al³⁺ + 3e^– → Al
  - M1: Only Al³⁺ + (3) e^– on the left [1]
  - M2: Equation fully correct [1]
- (iii)
  - M1: Anodes or carbon react(s) with oxygen [1]
  - M2: Form carbon dioxide [1]

10.1.1 Chemical Tests for Water Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe how cobalt chloride paper can be used to test for the presence of water. [2]

..........................................................................................................................................

..........................................................................................................................................
Mark Scheme (Q1):
- (changes from) blue (1)
- (to) pink (1)

Solution Q1

Cobalt chloride paper changes from blue to pink in the presence of water.

Q2: Anhydrous copper(II) sulfate is used to test for water. State the colour change in this test. [2]

from .................................................................................................

to ....................................................................................................
Mark Scheme (Q2):
- (from) white (1)
- (to) blue (1)

Solution Q2

Anhydrous copper(II) sulfate changes from white to blue in the presence of water.

10.1.2 Treatment of Water Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

10.2 Fertilisers Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

10.3.1 Composition of Air Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

10.3.2 Air Pollutants-Sources and Effects Paper 4 IGCSE Chemistry Topic Questions

Q: In which row is the air pollutant not correctly matched with its source?

Row	Air Pollutant	Source
A	carbon monoxide	incomplete combustion of fuels
B	lead compounds	burning petrol in cars
C	nitrogen oxides	decomposing vegetation
D	sulfur dioxide	burning coal and other fossil fuels

Answer: C

Solution

The correct answer is C.

Nitrogen oxides (NO and NO₂) are produced mainly by the reaction of nitrogen and oxygen gases in the high temperatures of car engines and power stations.

They are not formed by decomposing vegetation. Decomposition of vegetation releases carbon dioxide, methane, and other gases, but not nitrogen oxides.

Therefore, row C is incorrectly matched, making it the correct choice.

10.3.3 Environmental Issues Paper 4 IGCSE Chemistry Topic Questions

View All Member Area Resources

Q:
- (i) Describe two environmental problems caused by the disposal of plastic (polymer) waste. [2]
- (ii) The best way of disposing of plastic waste is recycling to form new plastics. What is another advantage of recycling plastics made from petroleum? [1]

Mark Scheme:
- (i) Any two of:
  - non-biodegradable / does not decompose → shortage of landfill space / visual pollution (1)
  - harmful / poisonous gases released when burnt (1)
  - dangerous to animals (ingestion / entanglement) (1)
- (ii) conserves petroleum / saves energy (1)

Solution

(i) Any two valid problems: plastics are non-biodegradable so they accumulate in landfill/visual pollution; burning plastics releases harmful gases; plastics are dangerous to animals (ingestion/entanglement).

(ii) Recycling plastics conserves petroleum (and saves energy).

10.3.4 Photosynthesis Paper 4 IGCSE Chemistry Topic Questions

Q: Answer the following questions using only the substances in the list. Each substance may be used once, more than once or not at all.

ammonia, bauxite, carbon dioxide, carbon monoxide, hematite, oxygen, sodium chloride, sulfur dioxide

(a) an element [1]
(b) an ore of iron [1]
(c) used to bleach wood pulp [1]
(d) used to manufacture fertilisers [1]
(e) a toxic gas produced during the incomplete combustion of hydrocarbons [1]
(f) an ionic compound [1]
(g) a reactant in photosynthesis [1]
(h) a product of photosynthesis [1]

Mark Scheme:
- (a) oxygen (1)
- (b) hematite (1)
- (c) sulfur dioxide (1)
- (d) ammonia (1)
- (e) carbon monoxide (1)
- (f) sodium chloride (1)
- (g) carbon dioxide (1)
- (h) oxygen (1)

Solution

(a) An element → oxygen
(b) An ore of iron → hematite
(c) Used to bleach wood pulp → sulfur dioxide
(d) Used to manufacture fertilisers → ammonia
(e) Toxic gas from incomplete combustion → carbon monoxide
(f) An ionic compound → sodium chloride
(g) Reactant in photosynthesis → carbon dioxide
(h) Product of photosynthesis → oxygen

11.1.1 Homologous Series Paper 4 IGCSE Chemistry Topic Questions

Q1: Compounds in the same homologous series have the same general formula.

(i) Give two other characteristics of members of a homologous series.
.............................................................................................................................................. [2]

Mark Scheme:

Any two from: [2]

(contain the) same functional group
differ from one member to the next by a –CH₂– unit
trend in physical properties
similar chemical properties

11.1.2 Displayed and Structural Formulae Paper 4 IGCSE Chemistry Topic Questions

Q: Ethene and but-2-ene are alkenes.

(i) Draw the displayed formula of but-2-ene. [2]

Mark Scheme:
- Four C atoms shown with double bond between C2 and C3 (1)
- Rest of structure correct (1)

Solution

The displayed formula of but-2-ene must have:

✔ Four carbons in a chain
✔ Double bond between the 2nd and 3rd carbons
✔ All hydrogens correctly shown

11.1.3 Structural Isomers Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

11.1.4 Saturated and Unsaturated Compounds [ Hydrocarbons] Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe a test for an unsaturated hydrocarbon.

test .............................................................................................................................................
observations .............................................................................................................................. [2]

Mark Scheme:

aqueous bromine [1]
decolourises / goes colourless [1]

11.3.1 Fractional Distillation of Petroleum Paper 4 IGCSE Chemistry Topic Questions

Q1: Petroleum is a mixture of hydrocarbons, which can be separated into fractions.

● the name of the process used to separate the fractions
....................................................................................................................................................
● how this process separates the different fractions.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.................................................................................................................................................... [4]

Mark Scheme:

(fractional) distillation [1]
petroleum vaporised / heated / turned into a gas [1]
temperature gradient in column / column hotter at bottom / colder at top [1]
smaller hydrocarbons go further up the column / larger hydrocarbons stay near the bottom of the column [1]
different boiling points of fractions / alkanes / molecules / hydrocarbons [1]
fractions / molecules / hydrocarbons come off at different heights in the column [1]

11.3.2 Uses of Petroleum Fractions Paper 4 IGCSE Chemistry Topic Questions

Q1: Complete the table to show the name and uses of some petroleum fractions.

name of fraction	use of fraction
naphtha	making chemicals
kerosene	jet fuel
fuel oil	fuel for ships / fuel for (home) heating

[3]

Mark Scheme:

naphtha: making chemicals [1]
kerosene: jet fuel [1]
fuel oil: fuel for ships / fuel for (home) heating [1]

11.3.2 Alkane Reactions Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

11.5.1 Alkene Reactions Paper 4 IGCSE Chemistry Topic Questions

Q: Ethene is an alkene which reacts with bromine as shown in the equation:

C₂H₄ + Br₂ → C₂H₄Br₂

(a) Write the general formula of alkenes. [1]
(b) Describe the colour change seen when ethene is bubbled through aqueous bromine. [1]
(c) In this reaction only one product is formed from two reactants. Name this type of organic reaction. [1]

Mark Scheme:
- (a) C_nH_2n (1)
- (b) orange to colourless (1)
- (c) addition (1)

Solution

(a) The general formula of alkenes is C_nH_2n.

(b) When ethene is bubbled through bromine water, the colour changes from orange to colourless.

(c) This is an addition reaction because the bromine atoms add across the C=C double bond of ethene to form one product.

11.6.1 Alcohols Paper 4 IGCSE Chemistry Topic Questions

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Q: Ethanol, C₂H₅OH, belongs to the homologous series called alcohols.
(a) Write the general formula of alcohols. [1]
(b) Explain why ethanol cannot be described as a hydrocarbon. [1]
(c) Ethanol can be manufactured from different substances by reaction with steam or by fermentation.
- (i) Give the formula of the substance which reacts with steam to form ethanol. [1]
- (ii) Name a substance which will undergo fermentation to form ethanol. [1]
(d) Ethanol is a fuel. Write the chemical equation for the complete combustion of ethanol. [2]

Mark Scheme:
- (a) C_nH_2n+1OH [1]
- (b) Not all atoms are C or H (contains O) [1]
- (c)(i) C₂H₄ [1]
- (c)(ii) glucose [1]
- (d) C₂H₅OH + 3O₂ → 3H₂O + 2CO₂ [2]

Solution

(a) C_nH_2n+1OH

(b) Ethanol contains oxygen — it is not only C and H, so it isn’t a hydrocarbon.

(c)(i) C₂H₄ (ethene) (ii) glucose

(d) C₂H₅OH + 3O₂ → 3H₂O + 2CO₂

11.7.1 Carboxylic Acids Paper 4 IGCSE Chemistry Topic Questions

Q: A carboxylic acid Y has the structure shown:

(a) State the general formula of carboxylic acids. [1]
(b) Name carboxylic acid Y. [1]
(c) Write the molecular formula of carboxylic acid Y. [1]

Mark Scheme:
- (a) C_nH_2n+1COOH (1)
- (b) methanoic acid (1)
- (c) CH₂O₂ (1)

Solution

(a) The general formula of carboxylic acids is C_nH_2n+1COOH.

(b) Carboxylic acid Y is methanoic acid.

(c) The molecular formula of Y is CH₂O₂.

11.8.1 Polymers Paper 4 IGCSE Chemistry Topic Questions

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Q: (i) Under certain conditions ethene reacts with chlorine to produce chloroethene, as in the equation:
C₂H₄ + Cl₂ → C₂H₃Cl + HCl
State the type of chemical reaction shown. [1]
(ii) Chloroethene monomers are converted into the polymer poly(chloroethene). State the type of polymerisation that produces poly(chloroethene) from chloroethene. [1]

Mark Scheme:
- (i) substitution [1]
- (ii) addition (polymerisation) [1]

Solution

(i) The reaction is substitution because one hydrogen in ethene is replaced by chlorine, producing chloroethene and HCl.

(ii) Poly(chloroethene) (PVC) is formed by addition polymerisation of many chloroethene (vinyl chloride) molecules joining together without loss of small molecules.

11.8.2 Plastics Paper 4 IGCSE Chemistry Topic Questions

Q: Describe one pollution problem caused by non-biodegradable plastics. [1]

Mark Scheme:
- filling landfill sites
- gets stuck in animals’ digestive system
- animals get stuck in the plastic
- blocks drains
- stops light getting to plants under water

Solution

Non-biodegradable plastics can cause pollution problems such as:

✔ Getting stuck in animals’ digestive systems and harming them.
✔ Filling up landfill sites.
✔ Blocking drains and causing floods.
✔ Preventing sunlight from reaching aquatic plants.

11.8.3 Proteins Paper 4 IGCSE Chemistry Topic Questions

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Q: Proteins are natural polymers. Proteins are broken down into amino acids. The process is similar to how complex carbohydrates are broken down to give simple sugars.
- (i) Name the type of reaction in which proteins are broken down into amino acids. [1]
- (ii) Name two types of substance that are used to break down proteins into amino acids. [2]

Mark Scheme:
- (i) hydrolysis (1)
- (ii)
  - M1: acids (1)
  - M2: enzymes (1)

Solution

(i) Hydrolysis.

(ii) Any two: acids and enzymes.

12.1-Experimental Design Basics Paper 4 IGCSE Chemistry Topic Questions

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Q: The label on a bottle of orange drink states ‘contains no artificial colours’. A scientist thinks that the orange colour in the drink is a mixture of two artificial colours: Sunset Yellow (E110) and Allura Red (E129).
Plan an experiment to show that the orange colour in the drink does not contain these two artificial colours.
Your plan should describe the use of common laboratory apparatus and samples of E110, E129 and the orange colouring from the drink. [6]

Mark scheme (any six):
- Use paper chromatography.
- Draw a pencil baseline/origin on chromatography paper.
- Apply small spots of the drink colour on the baseline.
- Apply separate spots of E110 and E129 standards on the same baseline.
- Place the paper in a beaker with solvent depth below the baseline.
- Allow the solvent to travel up the paper (develop the chromatogram).
- Remove paper, mark solvent front and allow to dry.
- Use a ruler to measure distances / calculate and compare R_f values (or compare spot heights/positions).
- Conclusion: drink does not contain E110/E129 if no spots coincide with the standards (positions/R_f values differ).

Solution

Cut a strip of chromatography paper and draw a pencil baseline ~1 cm from the bottom.
Spot three samples on the line using capillaries: drink colour, E110, and E129 (label lightly in pencil). Let each spot dry; re-spot if needed to keep them small/concentrated.
Pour a small volume of suitable solvent into a beaker and cover with a watch glass. Ensure the solvent level is below the baseline.
Place the paper in the beaker so the bottom edge touches the solvent. Allow the solvent front to rise near the top.
Remove the paper, immediately mark the solvent front in pencil, and allow to dry.
Compare the drink’s spots with the E110 and E129 spots (by position/height) and/or calculate R_f values (distance spot ÷ distance solvent front).
Conclusion: If the drink shows no spot coincident with E110 or E129 (different positions/R_f values), it does not contain these artificial colours.

12.2 Titrations — Paper 4 IGCSE Chemistry Topic Questions

Q: A student determines the concentration of a solution of dilute sulfuric acid, H₂SO₄, by titration with aqueous sodium hydroxide, NaOH.

step 1: 25.0 cm³ of 0.200 mol/dm³ NaOH is transferred into a conical flask.
step 2: Three drops of methyl orange indicator are added to the conical flask.
step 3: A burette is filled with H₂SO₄.
step 4: The acid in the burette is added to the conical flask until the indicator changes colour. The volume of acid is recorded. This process is known as titration.
step 5: The titration is repeated several times until a suitable number of results is obtained.

(i) Name the piece of apparatus used to measure exactly 25.0 cm³ of 0.200 mol/dm³ NaOH in step 1. [1]
(ii) State the colour change of the methyl orange indicator in step 4. [1]
(iii) State how the student decides that a suitable number of results have been obtained. [1]

[Click here and use Add Image button for Question Diagram]
Mark Scheme:
- (i) pipette (1)
- (ii) yellow to orange (1)
- (iii) at least two results are within 0.2 cm³ or less (1)
[Click here and use Add Image button for Mark Scheme Table]

Solution

(i) The apparatus used to measure exactly 25.0 cm³ of NaOH solution is a pipette.

(ii) The methyl orange indicator changes colour from yellow to orange when the end point is reached.

(iii) A suitable number of results is obtained when at least two titration results are within 0.2 cm³ of each other.

12.3.1 Chromatography — Paper 4 IGCSE Chemistry Topic Questions

Q: A student investigated the dyes contained in different coloured inks using chromatography. Water was the solvent. The diagram shows how the student set up the apparatus.
(a) Identify two errors in the way the student set up the apparatus. [2]

(b) The student then carried out the chromatography correctly. The diagram shows the results.
(i) Which ink contains the greatest number of soluble dyes? [1]
(ii) Which two inks are made of a single soluble dye? [1]
(iii) From the chromatogram it is not possible to tell if the red ink contains different dyes. Suggest how the experiment could be changed to find out if the red ink contains different dyes. [1]
Mark Scheme:
- 1(a): spots/baseline below solvent level (1)
- 1(a): baseline drawn in ink (1)
- 1(b)(i): black (1)
- 1(b)(ii): yellow and blue (1)
- 1(b)(iii): use an organic solvent / different solvent (1)

Solution

(a) Errors in setup:
• The spots/baseline were placed below the solvent level.
• The baseline was drawn in ink instead of pencil.

(b) Chromatogram interpretation:
(i) The ink with the greatest number of soluble dyes is black.
(ii) The inks made of a single soluble dye are yellow and blue.
(iii) To test whether the red ink contains different dyes, the chromatography should be repeated using a different or organic solvent.

12.4.1-Separation Techniques Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

12.5.1 -Test for Gases Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe the test for sulfur dioxide. test: ______ and observations: ______ [2]

Test: (Aqueous) potassium manganate (VII) [1]
Observation: (Purple to) colourless [1]

12.5.2 -Identifying Ions Paper 4 IGCSE Chemistry Topic Questions

Q: Define market failure. [2]
Mark Scheme:
- Market failure is when the market mechanism / price mechanism / demand and supply (1).
- Does not lead to an efficient allocation of resources (1).

12.5.3 -Flame Tests Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe how to do a flame test on a sample of a salt. [2]

Mark Scheme:

(Compound/salt) on wooden splint or (nichrome/platinum) wire [1]
Into (roaring) Bunsen flame [1]

Q2: The names of the elements of Period 2 of the Periodic Table are shown.
lithium beryllium boron carbon nitrogen oxygen fluorine neon
Answer the following questions about these elements. Each element may be used once, more than once or not at all.
Identify the element which:
produces a red flame in a flame test.

Mark Scheme:

Lithium [1]

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IGCSE Chemistry Past Papers by Topic with Solutions | Free Resources

IGCSE Chemistry Past Papers by Topic with Solutions

1.1.1 Properties of Solids Liquids and Gases Paper 4 IGCSE Chemistry Topic Questions

Q1: (a) Use ideas about the movement and arrangement of particles to explain why:

1.1.2 Structure of Solids Liquids and Gases Paper 4 IGCSE Chemistry Topic Questions

Q1: (a) Complete the table, using ticks (✔) and crosses (✘), to describe the properties of gases, liquids and solids.

Mark Scheme:

1.1.3 State Changes Paper 4 IGCSE Chemistry Topic Questions

Q1: Substances can change state.

Mark Scheme:

1.1.4 Effect of Temperature and Pressure on Gases Paper 4 IGCSE Chemistry Topic Questions

Q1: Substances can change state.

Mark Scheme:

1.1.2 Diffusion Paper 4 IGCSE Chemistry Topic Questions

Q1: The elements shown are gases at room temperature and pressure (Hydrogen, Nitrogen, Oxygen, Chlorine).

Mark Scheme:

Q2: The rate of diffusion of a gas was studied.

Mark Scheme:

2.1.2 Atomic Structure Basics Paper 4 IGCSE Chemistry Topic Questions

Q1: Atoms and ions are made from small particles called electrons, neutrons, and protons.

Mark Scheme:

2.4 Ions and Ionic Bonds Paper 4 IGCSE Chemistry Topic Questions

Q1: State the meaning of the term ionic bonding. [2]

Mark Scheme:

5.1.1 Endothermic / Exothermic Reactions Basics Paper 4 IGCSE Chemistry Topic Questions

6.3.2 Effect of water and heat on the Reversible Reaction of Copper Sulfate and Cobalt Chloride Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe how cobalt chloride paper can be used to test for the presence of water. [2]

Mark Scheme (Q1):

Q2: Anhydrous copper(II) sulfate is used to test for water. State the colour change in this test. [2]

Mark Scheme (Q2):

Question:

Mark Scheme:

Solution:

10.1.1 Chemical Tests for Water Paper 4 IGCSE Chemistry Topic Questions

Q1: Describe how cobalt chloride paper can be used to test for the presence of water. [2]

Mark Scheme (Q1):

Q2: Anhydrous copper(II) sulfate is used to test for water. State the colour change in this test. [2]

Mark Scheme (Q2):

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