Halides (chemistry only) - AQA GCSE Chemistry Exam Questions

Practise 13 exam-style questions on Halides (chemistry only) for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.

13 questions
1–6 marks each
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13 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

A student wants to test a solution for halide ions.

Name the two solutions the student should add to the sample.

Model answer

Dilute nitric acid, followed by silver nitrate solution.

Explanation

Halide ions form precipitates with silver ions, so silver nitrate is the reagent. The nitric acid is added first to remove other ions, such as carbonate, that could also form precipitates.

Mark scheme

1 mark
(dilute) nitric acid
do not accept hydrochloric acid or sulfuric acid
1 mark
silver nitrate (solution)
allow AgNO₃; do not accept silver alone

Question 2

2 marks

Write the ionic equation for the reaction between silver ions and iodide ions to form silver iodide. Include state symbols.

Model answer

Ag⁺(aq) + I⁻(aq) → AgI(s)

Explanation

Silver ions (1+) and iodide ions (1−) combine in a 1 : 1 ratio. The ions are in solution and the silver iodide is the yellow solid precipitate.

Mark scheme

1 mark
Ag⁺ + I⁻ → AgI
1 mark
state symbols: Ag⁺(aq) + I⁻(aq) → AgI(s)
all three state symbols correct

Question 3

3 marks

A student tests three solutions with acidified silver nitrate solution. The student finds it difficult to decide whether one precipitate is white, cream or yellow.

Suggest why the student finds this difficult, and give two ways the student could identify the halide ion with more confidence.

Model answer

White, cream and pale yellow are similar colours, and different people judge colours differently, especially in small amounts. The student could make precipitates from known solutions of a chloride, a bromide and an iodide and compare them side by side with the unknown, in good light against a dark background.

Explanation

Colour judgements are subjective, which reduces confidence in the result. Comparing with known reference samples under the same conditions makes the identification more reliable.

Mark scheme

1 mark
the colours are similar / pale, and judging colour is subjective
max 3
1 mark
compare with precipitates made from known chloride, bromide and iodide solutions (side by side)
1 mark
view against a white / black background in good light
1 mark
use an instrumental method

Question 4

4 marks

A student adds excess silver nitrate solution to 25.0 cm³ of 0.200 mol/dm³ sodium chloride solution.

NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)

Relative atomic masses (Ar): Cl = 35.5, Ag = 108

Calculate the mass of silver chloride precipitate formed, giving the answer to 2 significant figures.

Model answer

moles of NaCl = (25.0 ÷ 1000) × 0.200 = 0.00500 mol
1 mol NaCl gives 1 mol AgCl, so moles of AgCl = 0.00500 mol
Mr of AgCl = 108 + 35.5 = 143.5
mass = 0.00500 × 143.5 = 0.7175 g = 0.72 g (2 significant figures)

Explanation

Silver nitrate is in excess, so the sodium chloride determines how much precipitate forms. Convert cm³ to dm³ before using the concentration, and only round at the end.

Mark scheme

1 mark
moles of NaCl = 0.0250 × 0.200 = 0.005(00) mol
1 mark
moles of AgCl = 0.005(00) mol
allow ecf; 1:1 ratio
1 mark
mass = 0.00500 × 143.5 = 0.7175 g
allow ecf; Mr of AgCl = 143.5
1 mark
0.72 (g)
allow ecf for an incorrect answer correctly given to 2 significant figures; correct answer with no working scores 4 marks

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