A student generates a gas by adding dilute hydrochloric acid to solid calcium carbonate. Which of the following tests correctly identifies the gas produced?
Show the answer and explanation
Correct answer
C. The gas turns limewater milky.
Principle or equation
Calcium carbonate reacts with hydrochloric acid to produce carbon dioxide gas. Carbon dioxide is identified by turning limewater (aqueous calcium hydroxide) milky due to formation of insoluble calcium carbonate.
Why this answer is correct
The reaction is CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g). CO2 does not support combustion (so glowing splint goes out), is not flammable (no pop), and does not bleach litmus. Limewater test is specific for CO2.
Example
Adding dilute HCl to marble chips produces bubbles. Passing the gas through limewater causes a white precipitate of CaCO3, confirming CO2.
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