AQA GCSE Chemistry Chemistry Paper 2 (Higher), November 2020: Question 1

8 marks · Low Demand difficulty · Short Answer

Identify ions and describe qualitative tests, including flame tests, sodium hydroxide precipitate tests, and tests for sulfate and iodide ions.

Practise this question

Question

Question text

01 This question is about chemical analysis.

A student tested copper sulfate solution and calcium iodide solution using flame tests.

This is the method used.

1. Dip a metal wire in copper sulfate solution.

2. Put the metal wire in a blue Bunsen burner flame.

3. Record the flame colour produced.

4. Repeat steps 1 to 3 using the same metal wire but using calcium iodide solution.

01.1 What flame colour is produced by copper sulfate solution?

[1 mark]

01.2 Calcium compounds produce an orange-red flame colour.

The student left out an important step before reusing the metal wire.

The student’s method did not produce a distinct orange-red flame colour using

calcium iodide solution.

Explain why.

[2 marks]

01.3 The student added sodium hydroxide solution to:

• copper sulfate solution

• calcium iodide solution.

Give the results of the tests.

*02* [2 marks]

Copper sulfate solution

Calcium iodide solution

01.4 To test for sulfate ions the student added dilute hydrochloric acid to

copper sulfate solution.

Name the solution that would show the presence of sulfate ions when added

to this mixture.

[1 mark]

01.5 To test for iodide ions the student added dilute nitric acid to calcium iodide solution.

Name the solution that would show the presence of iodide ions when added

to this mixture.

Give the result of the test.

[2 marks]

Solution

Result

Mark scheme

Show the mark scheme

Question 1

AO /

Question Answers Extra information Mark

Spec. Ref.

AO1

01.1 green allow blue-green 1 4.8.3.1

RPA 7

did not clean the metal wire 1

01.2 (between tests) AO3

or 4.8.3.1

copper sulfate (solution) is still RPA 7

present

(so) colours are mixed / blended 1

/ masked

(copper sulfate solution)

01.3 blue precipitate allow blue solid 1 AO1

4.8.3.2

RPA 7

(calcium iodide solution)

white precipitate allow white solid 1

01.4 barium chloride (solution) allow barium nitrate (solution) 1 AO1

4.8.3.5

RPA 7

AO1

01.5 silver nitrate (solution) 1 4.8.3.4

RPA 7

yellow precipitate allow yellow solid 1

allow pale yellow precipitate /

solid

Total 8

How to answer it

Chemical Analysis: Tests for Cations & Anions

What this question tests

This question assesses required practical knowledge of qualitative inorganic analysis (AQA Required Practical 7):

Flame tests: Recalling flame colours for metal cations (Cu²⁺) and understanding practical control variables (cleaning the wire to prevent masking).
Precipitation tests with sodium hydroxide: Identifying characteristic coloured hydroxide precipitates for transition and Group 2 metal ions (Cu²⁺ and Ca²⁺).
Anion identification tests: Recalling the chemical reagents and positive observations for sulfate ions (SO₄²⁻) and halide ions (I⁻).

Question 01.1 · 1 Mark

Flame Test for Copper(II) Ions

Identifying the characteristic flame colour of copper compounds

✅ Correct Answer

Green

Mark scheme: Allow blue-green [1 mark].

❌ Common Errors

Writing blue: Students confuse the blue colour of aqueous copper sulfate solution with the flame colour.
Guessing orange or red (typical of calcium or lithium).

Question 01.2 · 2 Marks

Evaluating the Flame Test Method

Explaining why failing to clean the wire leads to invalid results

✅ Correct Answer

The wire was not cleaned between tests / copper sulfate is still present [1 mark]
The flame colours are mixed / blended / masked [1 mark]

Both points needed for full marks: the procedural flaw + its visual impact.

🧠 Exam Technique

When an "Explain why" question gives an unexpected outcome, link:

Cause: What physical contamination remained on the wire?
Consequence: Use the exact scientific keyword masked or mixed to explain why a distinct flame was not seen.

💡 Key Knowledge

Standard Cleaning Method: Dip the nichrome or platinum wire into concentrated hydrochloric acid ( HCl ) and place it into a hot Bunsen flame until it burns with no colour before picking up the next sample.

Question 01.3 · 2 Marks

Precipitation Reactions with Sodium Hydroxide

Observing metal hydroxide precipitates

✅ Correct Answer

Copper sulfate solution: blue precipitate [1 mark]
Calcium iodide solution: white precipitate [1 mark]

"Precipitate" or "solid" is required. Allow: blue solid / white solid.

❌ Common Errors

Writing "turns blue" or "turns cloudy" without using the word precipitate or solid. You must state the state change!
Mixing up calcium (white precipitate, insoluble in excess NaOH) with aluminium (white precipitate that redissolves in excess NaOH).

💡 Key Knowledge

Ionic equations for precipitation:

Cu²⁺(aq) + 2OH⁻(aq) → Cu(OH)₂(s) (blue)
Ca²⁺(aq) + 2OH⁻(aq) → Ca(OH)₂(s) (white)

Question 01.4 · 1 Mark

Test for Sulfate Ions (SO₄²⁻)

Identifying the reagent used alongside hydrochloric acid

✅ Correct Answer

Barium chloride (solution)

Allow: barium nitrate (solution) [1 mark].

🧠 Exam Technique

Read carefully: the question states that dilute hydrochloric acid has already been added. It specifically asks for the solution that shows the presence of sulfate ions when added next.

Result if asked: a thick white precipitate of insoluble barium sulfate forms ( BaSO₄ ).

❌ Common Errors

Naming silver nitrate (that is used for halide ions, not sulfate ions).
Writing just "barium" instead of the compound name barium chloride.

Question 01.5 · 2 Marks

Test for Halide Ions: Iodide (I⁻)

Identifying the halide reagent and the resulting precipitate colour

✅ Correct Answer

Solution: silver nitrate (solution) [1 mark]
Result: yellow precipitate [1 mark]

Allow: yellow solid / pale yellow precipitate [1 mark].

💡 Key Knowledge: Halide Summary

Acidify with dilute nitric acid ( HNO₃ ), then add silver nitrate ( AgNO₃ ):

Chloride (Cl⁻) → White precipitate ( AgCl )
Bromide (Br⁻) → Cream precipitate ( AgBr )
Iodide (I⁻) → Yellow precipitate ( AgI )

❌ Common Errors

Confusing the colours: writing cream (bromide) or white (chloride) instead of yellow.
Writing "yellow solution" — halides form an insoluble silver halide precipitate.

Topics

Chemistry · Required Practicals · C8: Chemical Analysis · Required Practicals

Question and mark scheme from the AQA GCSE Chemistry examination, Chemistry Paper 2 (Higher), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.