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 and a colorless gas is produced that turns limewater milky. Which salt is present?
Show the answer and explanation
Correct answer
A. Potassium carbonate
Principle or equation
Carbonate ions react with acid to produce carbon dioxide gas, which turns limewater milky.
Why this answer is correct
Carbonates (CO3^2-) react with H+ to produce CO2 gas. CO2 turns limewater milky due to formation of CaCO3. Sulfate, chloride, and nitrate do not produce CO2 with dilute HCl.
Example
K2CO3 + 2HCl -> 2KCl + H2O + CO2; CO2 + Ca(OH)2 -> CaCO3(s) + H2O.
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