Testing for carbonates (CO3^2-)
3 marks · EasyState the reagent added to a sample to test for carbonate ions.
Describe what you would observe if carbonate ions are present after adding this reagent.
Explain how you would confirm that the gas produced is carbon dioxide.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) dilute acid (e.g. hydrochloric acid)
(b) Fizzing or bubbles of gas are seen
(c) Bubble the gas through limewater; the limewater turns cloudy/milky
Common mistakes: Incorrect reagent (e.g. sodium hydroxide); Incorrect observation (e.g. precipitate instead of bubbles); Testing with wrong chemical for CO2
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct reagent named (dilute acid, e.g. HCl).
B1 (b) · 1 mark · States correct observation (fizzing, bubbling, or gas released).
B1 (c) · 1 mark · Confirms gas is CO2 with limewater turning cloudy/milky.
Worked solution
a) The reagent added is dilute acid, such as hydrochloric acid.
b) If carbonate ions are present, bubbles or fizzing will be observed.
c) The gas is confirmed as carbon dioxide by bubbling it through limewater. If the limewater turns cloudy, this shows carbon dioxide is present.