Ionic EquilibriumHard

Question

The base imidazole has a Kb of 1.0 × 10–7 at 25°C. In what volumes should 0.02 M-HCl and 0.02 M imidazole be mixed to make 120 ml of a buffer at pH = 7?

Options

A.60 ml, 60 ml
B.40 ml, 80 ml
C.30 ml, 90 ml
D.20 ml, 100 ml

Solution

$B_{\left( \text{Imidazole} \right)} + H^{+} \rightleftharpoons BH^{+}$

$\frac{V \times 0.02}{120}\text{ M}\frac{(120 - V) \times 0.02}{120}\text{ M}0$

Final $\frac{(2V - 120) \times 0.02}{120}M0\frac{(120 - V) \times 0.02}{120}M$

$P^{OH} = P^{K_{b}} + \log\frac{\left\lbrack BH^{+} \right\rbrack}{\lbrack B\rbrack_{0}} \Rightarrow 7 = 7 + \log\frac{120 - V}{2V - 120} \Rightarrow V = 80$

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