Cambridge IGCSE Chemistry Paper 1 and Paper 2: multiple-choice questions

Paper 1 and Paper 2: the same format, different content scope

Feature	Paper 1	Paper 2
Route	Core	Extended
Content	Core	Core + Supplement
Time	45 minutes	45 minutes
Questions	40 compulsory four-option MCQs	40 compulsory four-option MCQs
Marks / weighting	40 marks / 30%	40 marks / 30%
Assessment objective	AO1 + AO2	AO1 + AO2

A Multiple Choice Question (MCQ) is not merely a memory task. Under the official Cambridge weighting, Paper 1/2 assesses AO2 handling information and problem-solving as well as AO1 knowledge. A question may introduce a new graph, experimental situation or decision built from several statements.

Always practise questions for the correct route. Paper 1 requires secure application of Core content; Paper 2 requires Core + Supplement content.

Why is recognising a familiar answer not enough?

Incorrect options—the distractors—model common errors: a reversed periodic trend, omitted mole ratio, wrong ionic charge, faulty unit conversion or ignored condition. The familiar-sounding statement may therefore be the trap.

Ask of every option:

• is it true in this chemical system;
• are all stated conditions satisfied;
• are the number and unit both correct;
• does it claim a cause or only a correlation;
• does it contain an overstatement such as “always” or “only”?

The five-step MCQ routine

The five-step MCQ routine

01Read

Underline the negative, comparative or limiting word.

02Predict

State the chemical principle before looking for a matching option.

03Work out

Use a short calculation, relationship or trend direction.

04Eliminate

Give a scientific reason for rejecting each tempting option.

05Check

Confirm the question number and the exact task.

1. Read the stem. Underline the negative or comparative word: not, decreases, greatest, same. 2. Predict. State the chemical principle before considering the options. 3. Work it out. Show a short calculation; for a trend, name its direction and cause. 4. Eliminate. Do not write “looks odd”; state, for example, that charge is not conserved. 5. Check. Ensure the chosen letter belongs to the correct question number and answers the exact question.

Original exam-style example 1 – particles

The temperature of a gas in a sealed container increases while its volume remains constant. Which statement explains the increase in pressure?

A. The particles become larger.
B. The particles move faster and collide with the walls more frequently with a greater change in momentum.
C. More particles are created.
D. The spaces between particles disappear.

Correct: B. Repairing the distractors: A confuses particle size with motion; C violates the fixed particle number in a sealed system; D contradicts the particle model of a gas.

Calculation MCQs: do not calculate all four options

Write the required relationship, substitute with units, then compare the result with the options. If their orders of magnitude differ widely, estimate first to eliminate options.

Anatomy of an attractive distractor

01Attractive

It matches a familiar phrase or an incomplete relationship.

02Wrong step

The error may reverse a ratio, ignore a condition or use the wrong unit.

03Repair

Write the principle that eliminates it before memorising the letter.

Original exam-style example 2 – stoichiometry

Mg + 2HCl → MgCl₂ + H₂. How many moles of HCl are needed to react completely with 0.030 mol of Mg?

A. 0.015 mol
B. 0.030 mol
C. 0.060 mol
D. 0.090 mol

Correct: C. The mole ratio Mg:HCl is 1:2. A reverses the ratio; B omits the equation ratio; D incorrectly uses 1:3. The moles and stoichiometry guide develops the full calculation decision system.

Graphs and tables: read first, explain second

First identify the axes, units and stated range. Then decide whether the question asks for a description, interpolation, gradient interpretation or chemical explanation.

Common errors include:

• reversing the axes;
• claiming a general trend from one point;
• confusing “faster” with “more product was formed”;
• reading a point-to-point broken line instead of the line of best fit;
• omitting the unit from a value.

On the same axes, a steeper rate graph indicates a faster initial rate. The height of the final plateau may instead indicate the total amount of product—not the same question.

Conceptual traps: write a three-word reason for yourself

Original exam-style example 3 – equilibrium

A closed system is at dynamic equilibrium. Which statement is correct?

A. The reactions have stopped.
B. The concentrations of reactants and products must be equal.
C. The forward and reverse reactions have equal rates.
D. No particles move in the system.

Correct: C. A confuses macroscopic constancy with reactions stopping; B confuses constant concentration with equal concentration; D is the opposite of “dynamic”.

During correction, name a short rule: “rates are equal”, “charge is conserved”, “mole ratio from equation”, “volume in dm³”. These can become targeted mini-cards, but always test their use in a new question.

What should you do when two options remain?

1. State the single difference between the two answers.
2. Find the datum or condition in the stem that decides between them.
3. Create a counterexample: when would the other option be correct?
4. For a calculation, check ratio and unit instead of repeating the same working.
5. If still unsure, mark it and move on; return with fresh attention in the second pass.

For example, if two options differ only between 0.20 and 200 mol/dm³, the key is probably the cm³ → dm³ conversion, not the entire chemical model.

45 minutes, 40 questions: a three-pass timing strategy

45 minutes, 40 questions: three passes

01Pass 1

Answer secure, fast questions and flag anything that needs work.

02Pass 2

Return to calculations and questions needing a short method.

03Pass 3

Check units, signs, question numbers and unanswered items.

The average is slightly over one minute per question, but every question does not need equal time. A fast conceptual item funds a longer calculation. Do not spend 4–5 minutes on one difficult question in the first pass; mark it and return.

During practice, track separately:

• how many questions the first pass reached;
• how many correct answers were changed without a reason;
• which question types consumed too much time;
• whether time remained to check answer positions and question numbers.

Repairing the distractor matters more than copying the correct letter

Sample error log:

Question	Chosen option	Why was it tempting?	First wrong decision	Repair task	Reattempt
P2 / own Q6	B	the trend looked familiar	did not check direction down the group	two new trend questions with reasons	Friday
P2 / own Q9	D	the calculator gave it	did not convert cm³ to dm³	three concentration conversions	72 hours

Do not record “I was careless”. State which checking step was missing. Do not repeat the same item immediately from memory; use new numbers or a new context.

A weekly 20-minute MCQ routine

• 8 minutes: 6–8 mixed questions without help or notes.
• 5 minutes: identify the first decision behind every incorrect or uncertain answer.
• 4 minutes: refute the two most important distractors chemically in one sentence each.
• 3 minutes: create or solve one similar mini-question or unit check.

Add a short reattempt two or three days later. In the 8-week plan, MCQs return every week while the timed block gradually lengthens.

Self-check before the next block

• I use Paper 1 or Paper 2 questions matching my route.
• I state the expected chemical answer before reading the options.
• In calculations, I show at least the relationship, ratio and unit.
• When two options remain, I can name the deciding difference.
• I record a specific first wrong step for every incorrect answer.
• Timed blocks include a checking pass.

Paper 1/2 contributes 30% of the qualification. Multiple-choice accuracy should therefore develop alongside Paper 3/4 structured answers and Paper 5/6 AO3 skills.