Testing for carbonates (CO3^2-)
2 marks · NormalDescribe how you would test a solid sample to show that it contains carbonate ions (). State what you would observe if carbonate ions are present.
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Also accept: Add dilute acid to the solid and look for fizzing; if gas is produced, bubble it through limewater which goes cloudy if carbonate ions are present.
Common mistakes: Describing flame tests; describing unrelated tests for other ions.
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Marking points
M1 · 1 mark · States to add dilute acid to the solid sample; or to add a dilute acid to test for carbonate ions.
A1 · 1 mark · States that fizzing or bubbles of gas are seen, or that the gas turns limewater milky/cloudy.
Worked solution
To test for carbonate ions, add a little dilute acid (such as dilute hydrochloric acid) to the solid sample.
If carbonate ions are present, bubbles of gas will be given off (fizzing).
You can confirm the gas is carbon dioxide by bubbling it through limewater: the limewater will turn cloudy if carbonate ions are present.