Test for oxygen - AQA GCSE Chemistry Exam Questions

Practise 10 exam-style questions on Test for oxygen 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.

10 questions
1–5 marks each
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10 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 adds a small amount of manganese(IV) oxide to hydrogen peroxide solution in a test tube. Bubbles of oxygen are given off.

Describe a test the student could do to show that the gas is oxygen. Give the result of the test.

Model answer

Insert a glowing splint into the test tube of gas. If the gas is oxygen, the splint relights.

Explanation

The oxygen test needs a glowing splint (a splint that has been lit and then blown out). Relighting is the result; a squeaky pop is the hydrogen test, so do not mix them up.

Mark scheme

1 mark
put a glowing splint into the test tube / gas
do not accept burning / lighted splint
1 mark
the splint relights
dependent on a glowing splint being used; allow bursts into flame; do not accept 'burns more brightly' or 'pop'

Question 2

2 marks

A student collects the gas given off by some pondweed in bright light. When the student puts a glowing splint into the gas, it relights.

The student concludes: "The gas is pure oxygen."

Is the student's conclusion justified? Give a reason for your answer.

Model answer

No. A relighting splint shows that the gas contains a high proportion of oxygen, but it does not show that the gas is pure; small amounts of other gases such as carbon dioxide or nitrogen could also be present.

Explanation

Chemical tests like this identify a substance but do not show purity or measure how much is there. A splint will relight in oxygen that is mixed with other gases, as long as the proportion of oxygen is high.

Mark scheme

1 mark
no / not justified
1 mark
the test only shows the gas contains a high proportion of oxygen; other gases could also be present
allow the gas could contain some carbon dioxide / nitrogen / water vapour; allow the splint can relight without the oxygen being pure

Question 3

3 marks

The diagram shows apparatus used for the electrolysis of sodium sulfate solution. Tube A collects the gas from the negative electrode (cathode). Tube B collects the gas from the positive electrode (anode).

Identify the gas collected in tube B and describe a test to show that it is this gas.

Diagram of an electrolysis cell. Label A points to the upside-down test tube over the left electrode; label B points to the upside-down test tube over the right electrode; "sodium sulfate solution" labels the liquid in the container.

Model answer

The gas in tube B is oxygen. Put a glowing splint into the tube of gas; the splint relights.

Explanation

At the anode, sulfate ions are not discharged, so oxygen is produced from the water instead. The glowing splint test confirms it; hydrogen is formed in tube A at the cathode.

Mark scheme

1 mark
oxygen
allow O₂
1 mark
put a glowing splint into the gas / tube
do not accept burning / lighted splint
1 mark
the splint relights
dependent on a glowing splint being used

Question 4

4 marks

A student tests three gas samples, X, Y and Z. The table shows the results.

Identify gas X and gas Y. Explain why the student cannot identify gas Z from these results.

Table with columns "Gas", "Glowing splint put into gas", "Burning splint at open end". Gas: X; Glowing splint put into gas: Relights; Burning splint at open end: Burns more brightly | Gas: Y; Glowing splint put into gas: Not tested; Burning splint at open end: Squeaky pop | Gas: Z; Glowing splint put into gas: Goes out; Burning splint at open end: Goes out.

Model answer

Gas X is oxygen because it relights a glowing splint. Gas Y is hydrogen because it gives a squeaky pop with a burning splint. Gas Z is neither oxygen nor hydrogen, but many gases (for example carbon dioxide or nitrogen) put out both splints, so the student needs another test, such as limewater, to identify it.

Explanation

Each gas test has one specific positive result. A negative result only rules gases out, so a gas that gives no positive result in either splint test has to be identified with a different test.

Mark scheme

1 mark
X is oxygen
1 mark
Y is hydrogen
1 mark
Z is not oxygen or hydrogen / Z does not support burning
1 mark
several different gases put out both splints, so another test is needed
allow e.g. it could be carbon dioxide or nitrogen; allow 'test it with limewater' as the further test

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