Degree 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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