AQA GCSE Chemistry (8462), Higher tier · Chemical analysis › Identification of common gases
Practise Test for oxygen. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Pondweed was placed in a beaker of water in bright light. Bubbles of gas were given off. The gas was collected in an upside-down test tube filled with water. Name the process in the pondweed that produced the oxygen.
photosynthesis
Complete the sentences using words from the list. burning glowing goes out pops relights The test for oxygen uses a .................... splint. If the gas is oxygen, the splint ....................
glowing; relights
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy2 marks
(a) Which test result shows that a gas is oxygen? Tick (✓) one box.[1]
A burning splint gives a squeaky pop
A glowing splint relights
Limewater turns milky
Damp litmus paper is bleached
(b) Air contains about 20% oxygen, but a test tube of air does not give a positive result in the test for oxygen. Suggest why.[1]
Show the answer and mark scheme
(a)Answer: A glowing splint relights
(b)
the concentration / percentage of oxygen in air is too low (to relight a glowing splint)
Question 2Medium4 marks
A student added manganese(IV) oxide to hydrogen peroxide solution. The hydrogen peroxide decomposed. 2H2O2(aq) → 2H2O(l) + O2(g) The student collected the gas in test tubes over water.
(a) Describe the test for the gas produced and give the result.[2]
(b) The first test tube of gas collected gave a negative result in this test. The second test tube gave a positive result. Suggest why the first test tube of gas gave a negative result.[1]
(c) The second test tube of gas was left open for 10 minutes and then tested again. This time the result was negative. Suggest why.[1]
Show the answer and mark scheme
(a)
put a glowing splint into the test tube (of gas)
the splint relights
(b)
the first tube contained (mainly) air that was pushed out of the flask / delivery tube
(c)
the oxygen escaped / mixed with air (so its concentration was too low)
Question 3Hard5 marks
A student electrolyses dilute sulfuric acid using inert electrodes, and collects the gas produced at the positive electrode (anode) in a test tube.
(a) Predict the gas produced at the positive electrode. Explain your prediction.[2]
(b) Describe how the student could test this gas to confirm it is oxygen, and state the result.[2]
(c) The volume of gas collected at the positive electrode is about half the volume collected at the negative electrode in the same time. Suggest why.[1]
Show the answer and mark scheme
(a)Answer: oxygen
oxygen
hydroxide ions (from the water) are oxidised / lose electrons at the positive electrode, forming oxygen gas
(b)
insert a glowing splint into the tube of gas
the splint relights
(c)
hydrogen and oxygen are formed in a 2 : 1 mole ratio (from water), and equal amounts in moles of any gas occupy equal volumes, so half as much oxygen as hydrogen is produced by volume