AQA GCSE Chemistry (8462), Higher tier · Chemical analysis › Identification of common gases
Practise Test for carbon dioxide. 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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Name the solution used to test for carbon dioxide.
limewater
Complete the word equation. carbon + oxygen → ....................
carbon dioxide
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy3 marks
(a) Name the solution used to test for carbon dioxide.[1]
(b) Describe how the gas should be added to the solution.[1]
(c) Give the result if the gas is carbon dioxide.[1]
Show the answer and mark scheme
(a)Answer: limewater
limewater / calcium hydroxide solution
(b)
bubble the gas through the solution / shake the gas with the solution
(c)
(the solution) turns milky / cloudy
Question 2Medium3 marks
Limewater is calcium hydroxide solution. This equation shows the reaction of carbon dioxide with limewater. Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
(a) Use the equation to explain why limewater turns milky when carbon dioxide is bubbled through it.[2]
(b) A student bubbled exhaled breath through one tube of limewater and bubbled the same volume of air from the room through another tube of limewater. Suggest why the limewater turned milky more quickly with the exhaled breath.[1]
Show the answer and mark scheme
(a)
calcium carbonate is formed
calcium carbonate is insoluble / is a solid / forms a precipitate (shown by the state symbol (s))
(b)
exhaled breath contains a higher concentration / percentage of carbon dioxide (than air)
Question 3Hard5 marks
A technician has three test tubes of gas. One contains hydrogen, one contains oxygen and one contains carbon dioxide, but the tubes are not labelled.
(a) Describe tests the technician could use to identify all three gases. Give the result of each test.[3]
(b) The technician identifies the carbon dioxide and the oxygen, and then labels the third tube 'hydrogen' without testing it. Evaluate this decision.[2]
Show the answer and mark scheme
(a)
bubble each gas through limewater: the gas that turns limewater milky is carbon dioxide
put a glowing splint into each of the other gases: the gas that relights it is oxygen
hold a lit splint at the mouth of the tube: the gas that burns with a squeaky pop is hydrogen
(b)
the conclusion is only correct if the tubes really do contain just these three gases (e.g. a tube could have leaked, or the tubes could have been mixed up with others)
so the third gas should still be confirmed with its own positive test (a squeaky pop with a lit splint), rather than by elimination alone