WAEC Chemistry 2013 Objective — Question 29

Question 29 of 50 from the West African Examinations Council (WAEC) Chemistry 2013 Objective paper, with the correct answer and a full explanation.

Which of the following acids would readily react with CaCO3 to liberate CO2?

A. CH3COOH
B. H2SO4
C. H2SO3
D. HNO3Correct

Explanation

One could have expected that H2SO4 and HNO3 to react to the same extent with CaCO3 to give CO2 since they are both strong acids. However, H2SO4 will react with CaCO3 to produce CaSO4 which is only sparingly soluble. This CaSO4 can form a protective layer over the CaCO3, thereby preventing further reaction. HNO3, on the other hand, will react smoothly and flawlessly as all nitrates are soluble. CaCO3(s)+2HNO3(aq)→Ca(NO3)2(aq)+H2O(l)+CO2(g).

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