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8.3.5Sulfates

AQA GCSE Chemistry (8462), Higher tier · Chemical analysis › Identification of ions

Practise Sulfates. 14 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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Required practical: Identifying ions (method, variables and exam tips)

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Name the acid that is added to the sample before this solution.
dilute hydrochloric acid
The solution contained sodium sulfate.
Name the white precipitate formed.
barium sulfate
Write the ionic equation for the reaction between barium ions and sulfate ions.
Include state symbols.
Ba2+(aq) + SO42−(aq) → BaSO4(s)
Complete the ionic equation for the reaction in the test for sulfate ions.
Ba2+(aq) + .................... → BaSO4(s)
SO42−(aq)

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 solution is used in the test for sulfate ions?
Tick (✓) one box.[1]
  • Barium chloride solution
  • Limewater
  • Silver nitrate solution
  • Sodium hydroxide solution
(b) Name the acid that is added to the sample before this solution.[1]
(c) Give the result of a positive test for sulfate ions.[1]
Show the answer and mark scheme
(a) Answer: Barium chloride solution
(b) Answer: dilute hydrochloric acid
  • (dilute) hydrochloric acid
(c) Answer: white precipitate
  • white precipitate
Question 2Medium6 marks
A student tests a solution for sulfate ions by adding dilute hydrochloric acid and then barium chloride solution.
(a) Why is dilute hydrochloric acid added first?[1]
(b) Explain why dilute sulfuric acid must not be used instead of hydrochloric acid.[2]
(c) The solution contained sodium sulfate.
Name the white precipitate formed.[1]
(d) Complete the balanced equation for the reaction.
BaCl2(aq) + Na2SO4(aq) → .................... + ....................[2]
Show the answer and mark scheme
(a)
  • to remove / react with carbonate ions (which would also form a white precipitate with barium ions)
(b)
  • sulfuric acid contains sulfate ions
  • so a white precipitate would form whatever the sample contained
(c) Answer: barium sulfate
  • barium sulfate
(d) Answer: BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
  • BaSO4 and NaCl (correct formulae of both products)
  • 2 in front of NaCl
Question 3Hard6 marks
Barium chloride solution is used to test for sulfate ions.
(a) Write the ionic equation for the reaction between barium ions and sulfate ions.
Include state symbols.[2]
(b) A student added barium chloride solution to sodium carbonate solution without adding acid first. A white precipitate formed.
Suggest the identity of the white precipitate.[1]
(c) Explain how adding dilute hydrochloric acid first prevents this precipitate forming.
Include an ionic equation in your answer.[3]
Show the answer and mark scheme
(a) Answer: Ba2+(aq) + SO42−(aq) → BaSO4(s)
  • Ba2+ + SO42− → BaSO4
  • (aq) (aq) → (s)
(b) Answer: barium carbonate
  • barium carbonate
(c)
  • hydrogen ions (from the acid) react with carbonate ions
  • CO32− + 2H+ → CO2 + H2O
  • so no carbonate ions remain to form a precipitate with barium ions

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