alleryDegree of dissociation α of weak acid HA (Ka = 1.8 × 10⁻⁵) in 0.01 M solution:
A≈0.04
B≈0.18
C≈4.2 × 10⁻² (4.2 percent)
D≈0.4
Answer & Solution
Correct answer: C. ≈4.2 × 10⁻² (4.2 percent)
**For weak acid:** α = √(Ka/C) for small α.
α = √(1.8 × 10⁻⁵ / 10⁻²) = √(1.8 × 10⁻³) ≈ 0.0424 ≈ 4.2 percent.
**So about 4.2 percent of acid molecules dissociate.**
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