Edexcel Chemistry: papers and exam technique — Edexcel GCSE Chemistry revision

How science papers are typically structured

• Chemistry papers commonly combine objective (multiple-choice) questions, short structured questions, calculation questions, and at least one extended 6-mark response question.
• Marks are distributed across recall of facts, application of ideas to unfamiliar substances or reactions, and interpretation of experimental data.
• Some questions are synoptic, drawing together ideas from more than one topic, such as combining bonding with reactivity.
• Always check the current specification and specimen papers on your exam board's own website, since paper structure and question styles can be revised between years.
• Look carefully at how many marks a question is worth and how much space is given, as both indicate the expected depth of your answer.

Command words and what they demand

• 'State' or 'Name' wants a short factual answer; 'Describe' wants what is observed or what happens without giving reasons.
• 'Explain' always needs a reason or mechanism, often linked to particle theory, bonding or reactivity trends.
• 'Calculate' needs a full numerical method, correct units, and an appropriate number of significant figures.
• 'Balance' means adjusting numbers in front of formulae (not subscripts) so atoms of each element match on both sides of an equation.
• 'Evaluate' asks for a balanced judgement of a method or set of results, including limitations, leading to a conclusion.

Key terms

Evaluate

Weigh up strengths and weaknesses and reach a justified overall judgement.

Predict

Use a pattern or trend to suggest an untested outcome.

Independent variable

The factor that is deliberately changed in an investigation.

Dependent variable

The factor that is measured as a result of the change.

Control variable

A factor kept constant so a test is fair.

Relative formula mass (Mr)

The sum of the relative atomic masses of all atoms in a formula.

Common exam traps

• Balancing equations by changing subscripts instead of the numbers in front of formulae.
• Forgetting to work out relative formula mass correctly before starting a moles calculation.
• Giving a calculation answer with no working shown, losing method marks.

Practice questions with answers

1. 1. Which command word requires a reason or mechanism, not just an observation?

   • • Describe
   • • Explain
   • • State
   • • Name

   Answer: Explain

   'Explain' requires a reason linking cause and effect, often referring to particle theory or bonding.

2. 2. When balancing a chemical equation, what should you change?

   • • Subscripts within formulae
   • • Numbers in front of formulae
   • • Element symbols
   • • State symbols

   Answer: Numbers in front of formulae

   Balancing is done by adjusting the number of each formula unit, not by altering subscripts, which would change the substance.

3. 3. Calculate the relative formula mass of CaCO3 (Ar: Ca = 40, C = 12, O = 16).

   Answer: 100

   Mr = 40 + 12 + (16 × 3) = 40 + 12 + 48 = 100.

4. 4. Calculate the number of moles in 20 g of CaCO3 (Mr = 100).

   Answer: 0.2 mol

   Moles = mass ÷ Mr = 20 ÷ 100 = 0.2 mol.

5. 5. In an investigation of reaction rate at different acid concentrations, what is the independent variable?

   • • Volume of gas produced
   • • Acid concentration
   • • Temperature
   • • Type of acid

   Answer: Acid concentration

   The independent variable is the factor deliberately changed by the experimenter.

More free Chemistry revision

• All Edexcel Chemistry revision pages
• All GCSE Chemistry topics
• Edexcel Chemistry: Atoms, elements and the periodic table
• Edexcel Chemistry: Ionic, covalent and metallic bonding
• Edexcel Chemistry: Moles, masses and conservation
• Edexcel Chemistry: Rates of reaction and energy changes
• Edexcel Chemistry: Chemical changes: reactivity, acids and electrolysis
• Edexcel Chemistry: Energy changes: exothermic, endothermic and bond energies
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