A colorless solution is known to contain only one of the following salts: potassium carbonate, potassium sulfate, potassium chloride, or potassium nitrate. When a few drops of dilute hydrochloric acid are added, effervescence occurs. Which salt is present?
Show the answer and explanation
Correct answer
A. Potassium carbonate
Principle or equation
Carbonate salts react with acids to produce carbon dioxide gas, which causes effervescence. Sulfates, chlorides, and nitrates do not produce a gas with dilute hydrochloric acid.
Why this answer is correct
When dilute hydrochloric acid is added to a carbonate, the reaction is: CO₃²⁻ + 2H⁺ → CO₂(g) + H₂O. The carbon dioxide gas is released as bubbles, so effervescence indicates the presence of carbonate ions. Therefore, the salt must be potassium carbonate.
Example
Sodium carbonate reacts with hydrochloric acid: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂↑.
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