Apentix/AP Chemistry/Unit 4: Chemical Reactions/Question
AP Chemistryeasymcq1 pt

Bubbles form at once when aqueous K₂CO₃ is mixed with aqueous HCl. Which gas escapes, and why?

A.CO₂, released when unstable carbonic acid decomposes
B.H₂, released by acid attacking potassium ions
C.O₂, released by breakdown of the carbonate ion
D.HCl vapor, driven off by local heating

Explanation

Core Concept

Double replacement first assembles H₂CO₃ alongside KCl. Carbonic acid is unstable in water and instantly fragments into liquid water and CO₂ gas, whose escaping bubbles drive the exchange to completion. Gas evolution joins precipitate formation and weak-electrolyte creation as the three events that pull ionic metathesis reactions forward.

Correct Answer

ACO₂, released when unstable carbonic acid decomposes

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