Testing for carbonates (CO3^2-)
3 marks · EasyA teacher gives you a sample to test for carbonate ions. Describe fully how you would carry out this test.
State how you would know if carbonate ions are present.
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.
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(a) Add dilute acid (such as hydrochloric acid) to the sample in a test tube and look for bubbling. If gas is produced, bubble it through limewater and see if the limewater turns cloudy.
(b) If limewater turns cloudy, carbonate ions are present.
Common mistakes: forgetting to test gas with limewater; vague answers (just 'bubbles')
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Adds dilute acid to sample and observes for gas.
M1 (a) · 1 mark · Bubbles the gas through limewater and observes colour change.
B1 (b) · 1 mark · States that limewater turning cloudy shows carbonate ions are present.
Worked solution
a) Add dilute acid to the sample in a test tube. If fizzing occurs, collect the gas and bubble it through limewater. If the limewater turns cloudy, this confirms carbon dioxide is present.
b) Limewater turning cloudy (milky) means that carbonate ions are present.