Question

The rate constant at 25°C for the reaction of NH₄⁺& OH^– to form NH₄OH is 4 × 10¹⁰ M^–1 sec^–1&ionisation constant of aq. NH₃ is 1.8 × 10^–5. The rate constant of proton transfer to NH₃ is –

• A. 1.8 × 10^–5
• B. 7.2 × 10⁺⁵
• C. 3.6 × 10⁵
• D. 4.2 × 10^–5

Answer 1

Answer: (B)

7.2 × 10⁺⁵

Answer 2

NH₄⁺ + OH^– $\overset{\quad k_{1}\quad}{\rightarrow}$NH₄OH k₁ = 4 × 10¹⁰

NH₄OH $\frac { \mathrm { K } _ { \mathrm { f } } } { \stackrel { \mathrm { K } _ { \mathrm { b } } } { } }$ NH₄⁺ + OH^–

k_eq = $\frac{k_{f}}{k_{b}}$

1.8 × 10^–5 = $\frac{k_{f}}{4 \times 10^{10}}$ ̃ k_f = 7.2 × 10⁵