AP Chemistrymediummcq1 pt
A 0.50 M solution of methylamine, CH₃NH₂, has [OH⁻] = 0.011 M at equilibrium. What is Kb for methylamine?
A.2.5 × 10⁻⁴
B.1.2 × 10⁻⁴
C.2.2 × 10⁻²
D.1.0 × 10⁻¹⁴
Explanation
Core Concept
For B + H₂O ⇌ BH⁺ + OH⁻, Kb equals [BH⁺][OH⁻] divided by [B]. Equilibrium gives [BH⁺] = [OH⁻] = 0.011 M and [B] = 0.50 - 0.011 = 0.489 M. Substituting yields Kb = (0.011)(0.011) ÷ 0.489 ≈ 2.5 × 10⁻⁴.
Correct Answer
A2.5 × 10⁻⁴
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