Ionic EquilibriumHard

Question

A volume of 2.5 ml of 2/5 M weak monoacidic base (Kb = 1 × 10−12 at 25o C) is titrated with (2/15) M-HCl in water at 25o C. The concentration of H+ at equivalence point is (Kw = 1 × 10−14 at 25o C)

Options

A.3.7 × 10−13 M
B.3.2 × 10−7 M
C.3.2 × 10−2 M
D.2.7 × 10−2 M

Solution

For equivalence point, $2.5 \times \frac{2}{5} = V_{HCl} \times \frac{2}{15}$

∴ VHCl = 7.5 ml

$BOH + H^{+} \rightleftharpoons B^{+} + H_{2}O;K_{aq} = \frac{10^{- 12}}{10^{- 14}} = 10^{2} $$$\frac{2.5 \times \frac{2}{5}}{10}\text{ M}\frac{7.5 \times \frac{2}{15}}{10}\text{ M}0$$

0 0 0.1 M

Eqn. $x\text{ M}X\text{ M}(0.1 - x)\text{ M}$

$100 = \frac{0.1 - x}{x.x} \Rightarrow x = 2.7 \times 10^{- 2}\text{ M = }\left( H^{+} \right)$

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