A student generates a gas by adding dilute hydrochloric acid to solid sodium 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
The reaction between a carbonate and an acid produces carbon dioxide gas. Carbon dioxide is identified by turning limewater (calcium hydroxide solution) milky due to the formation of insoluble calcium carbonate.
Why this answer is correct
Sodium carbonate reacts with hydrochloric acid to produce sodium chloride, water, and carbon dioxide: Na2CO3 + 2HCl → 2NaCl + H2O + CO2. Carbon dioxide gas is colorless and odorless; it does not support combustion, so a glowing splint would not relight (it would extinguish). It does not produce a squeaky pop (that is hydrogen). It does not bleach litmus paper (that is chlorine). The standard test for CO2 is bubbling it through limewater, which turns milky due to CaCO3 precipitate.
Example
If a gas is evolved from adding acid to limestone, passing it through limewater will turn the solution cloudy, confirming CO2.
This published item includes a stored explanation and passed the platform’s publication workflow. It is independent preparation material, not a claim of an official or recalled examination question.