AQA GCSE Chemistry (8462), Higher tier · Chemical analysis › Identification of common gases
Practise Test for chlorine. 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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Sodium chlorate(I) has the formula NaClO. Balance the equation for the reaction between sodium chlorate(I) and hydrochloric acid. NaClO + ....HCl → NaCl + Cl2 + H2O
NaClO + 2HCl → NaCl + Cl2 + H2O
A student wants to find out whether a gas is chlorine. Name the type of paper used in the test for chlorine.
(damp) litmus paper
Predict the gas produced at the positive electrode. Explain your prediction.
chlorine
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) Which test result shows that a gas is chlorine? Tick (✓) one box.[1]
Damp litmus paper is bleached
Damp red litmus paper turns blue
A glowing splint relights
Limewater turns milky
(b) Why must the litmus paper be damp?[1]
(c) Give one safety precaution a student should take when testing for chlorine.[1]
Show the answer and mark scheme
(a)Answer: Damp litmus paper is bleached
(b)
so that the chlorine can dissolve in / react with the water (to bleach the paper)
(c)
use a fume cupboard / well-ventilated room (because chlorine is toxic)
Question 2Medium3 marks
A student electrolysed sodium chloride solution. A pale green gas was produced at the positive electrode.
(a) Describe the test to show that the gas is chlorine. Give the result.[2]
(b) Carbon dioxide is also an acidic gas. Suggest why carbon dioxide does not give the same result as chlorine in this test.[1]
Show the answer and mark scheme
(a)
hold damp litmus paper in the gas
the paper is bleached / turns white
(b)
carbon dioxide does not bleach the (litmus) paper / carbon dioxide would only turn (blue) litmus paper red
Question 3Hard6 marks
A technician electrolyses concentrated sodium chloride solution using inert electrodes. Gas is produced at both electrodes.
(a) Predict the gas produced at the positive electrode. Explain your prediction.[2]
(b) Write a half equation for the reaction at the positive electrode.[1]
(c) Describe how the technician could confirm that this gas is chlorine, and give the result.[2]
(d) Explain why this process is carried out with good ventilation or gas extraction, rather than relying on smell to detect any leaks.[1]
Show the answer and mark scheme
(a)Answer: chlorine
chlorine
chloride ions are attracted to the positive electrode, where they lose electrons (are oxidised) to form chlorine gas
(b)Answer: 2Cl− → Cl2 + 2e−
2Cl− → Cl2 + 2e−
(c)
hold damp (blue) litmus paper in a sample of the gas
the litmus paper is bleached / turns white
(d)
chlorine is toxic even at low concentrations, so relying on smell means some chlorine has already been inhaled before a leak is noticed