GCSE Chemistry — Practice Paper 1

Atomic structure, bonding, quantitative chemistry, chemical changes and energy changes — including the calculation questions that separate grades 7–9 from the rest.

How to use this: the quantitative questions carry disproportionate weight at the top grades and are the most learnable part of the paper. Do them first and check the working twice.

Section A — Short answer

1. State the relative charge and mass of a proton, neutron and electron (3 marks)

Where the marks sit: 1 per particle, both properties correct.

2. An atom of element X has 11 protons and 12 neutrons. Give its mass number and electron configuration (2 marks)

• Mass number = 11 + 12 = 23
• Configuration = 2, 8, 1

Common mistake: deriving the configuration from 23 rather than 11. Electrons equal protons, not mass number.

3. Explain why graphite conducts electricity but diamond does not (3 marks)

1. In graphite each carbon forms three covalent bonds, leaving one delocalised electron per atom
2. These delocalised electrons are free to move through the structure and carry charge
3. In diamond each carbon forms four covalent bonds, so there are no free electrons

Where the marks sit: 1 for three bonds in graphite, 1 for delocalised electrons carrying charge, 1 for four bonds in diamond leaving none.

This is a mechanism question. "Graphite has free electrons" alone is 1 mark of 3 — you must say how many bonds each forms and why that leaves an electron spare.

4. Explain why ionic compounds have high melting points (2 marks)

There are strong electrostatic forces of attraction between oppositely charged ions, acting in all directions throughout the giant ionic lattice, and a large amount of energy is needed to overcome them.

Where the marks sit: 1 for strong electrostatic attraction between oppositely charged ions, 1 for the giant lattice requiring much energy.

Common mistake: "strong bonds" — too vague, and it fails to name the type of force. AQA mark schemes require electrostatic.

Section B — Quantitative chemistry

5. Calculate the relative formula mass ($M_r$) of $\ce{Ca(OH)2}$ (2 marks)

(Ca = 40, O = 16, H = 1)

Ca            = 40
(OH) × 2  →  (16 + 1) × 2 = 34

M_r = 40 + 34 = 74

Answer: 74

The trap is the bracket. The subscript 2 applies to both O and H. Answering 57 means the bracket was ignored.

6. Calculate the number of moles in 12 g of carbon (2 marks)

(C = 12)

          mass        12
moles = --------- = ------ = 1 mol
           M_r        12

Answer: 1 mol

7. 4.8 g of magnesium reacts completely with oxygen. Calculate the mass of magnesium oxide formed (4 marks)

(Mg = 24, O = 16)

Equation:   2Mg + O₂ → 2MgO

Moles of Mg  = 4.8 / 24 = 0.2 mol

Ratio Mg : MgO is 2 : 2, i.e. 1 : 1
∴ moles of MgO = 0.2 mol

M_r of MgO = 24 + 16 = 40

Mass = moles × M_r = 0.2 × 40 = 8.0 g

Answer: 8.0 g

Where the marks sit: 1 for moles of Mg, 1 for using the balanced ratio, 1 for $M_r$ of MgO, 1 for the mass.

The four-step routine for every mass-to-mass calculation:
1. Balanced equation
2. Convert the known mass to moles
3. Apply the mole ratio from the equation
4. Convert back to mass

Skipping step 3 is the single most common source of lost marks in this topic.

8. In an experiment the theoretical yield was 8.0 g but only 6.4 g was obtained. Calculate the percentage yield (2 marks)

                actual yield
% yield  =  ------------------- × 100
             theoretical yield

         =  (6.4 / 8.0) × 100
         =  80%

Answer: 80%

Why yield is never 100%: the reaction may be reversible, product is lost on transfer or filtration, or side reactions occur. AQA often asks for a reason alongside the calculation.

Section C — Chemical and energy changes

9. Describe the test for hydrogen gas and give the result (2 marks)

• Test: hold a lit splint at the mouth of the tube
• Result: a squeaky pop

Where the marks sit: 1 for the test, 1 for the observation. Either alone is incomplete.

The four gas tests, which are guaranteed marks:

10. Explain, in terms of bond energies, why a reaction is exothermic (3 marks)

1. Breaking bonds is endothermic — it requires energy
2. Making bonds is exothermic — it releases energy
3. In an exothermic reaction, the energy released in making bonds is greater than the energy required to break them, so there is a net release

Where the marks sit: 1 per point, and the third must be an explicit comparison.

Memory aid: Breaking = Endothermic ("B before E"). Reversing these is the commonest error in the whole topic.

11. A student adds excess zinc to copper sulfate solution. Write the ionic equation and identify what is oxidised (3 marks)

Full equation:   Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Ionic equation:  Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
                 (sulfate is a spectator ion and is cancelled)

Zinc is OXIDISED — it loses two electrons, going from 0 to +2.

Where the marks sit: 1 for cancelling the spectator ion, 1 for the correct ionic equation, 1 for identifying zinc as oxidised with justification.

Displacement rule: a more reactive metal displaces a less reactive one. Zinc is above copper in the reactivity series, so the reaction proceeds.

What lifts a GCSE Chemistry grade

1. Learn the four gas tests. They recur every year and are pure recall.
2. Never skip the mole ratio. It is where mass-to-mass calculations are lost.
3. Say "electrostatic". Mark schemes for bonding questions name the force explicitly.
4. Bond breaking is endothermic. Get this right and the whole energetics topic follows.
5. Watch brackets in formulae. $\ce{Ca(OH)2}$, $\ce{Al2(SO4)3}$ — the subscript distributes.

Where to go next

• GCSE Physics Practice Paper 1 — the same calculation discipline applied to equations
• GCSE Biology Practice Paper 1 — extended-response technique
• A-Level Chemistry Practice Paper 1 — if you are continuing to sixth form

Ask StudyAI for more mole calculations at this level and it will mark each of the four steps separately.