The base-dissociation constant, Kb, for aniline is 4.3 × 10-10.What is the acid-dissociation constant for the conjugate acid of aniline?

For a base and its conjugate acid, Kb × Ka = Kw = 1.0 × 10⁻¹⁴ at 25°C. Thus, Ka = (1.0 × 10⁻¹⁴) ÷ (4.3 × 10⁻¹⁰) ≈ 2.3 × 10⁻⁵. The acid-dissociation constant is therefore 2.3 × 10⁻⁵, choice A.

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