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Problem 3 - Entrance Test

A 0.1 M solution of acetic acid (Ka = 1.8 × 10⁻⁵) is mixed with 0.2 M HCl. Calculate the degree of dissociation of acetic acid.

Correct: D

HCl provides [H⁺] = 0.2 M, suppressing acetic acid dissociation. Using Ka = [H⁺][CH3COO⁻]/[CH3COOH], solve for α = (Ka × 0.1)/[(0.2)^2] = 4.5 × 10⁻⁵.