Answer to Question #151408 in Inorganic Chemistry for robert

Question

Calculate or hydrolysis a 0.1 KCN solution at 25 oC. The HCN ionization constant is 7.0 x 10-10 and the ionic product of water is 1.0 x 10-14.

Answer 1

$CN^- + H_2O \quad^\to _\leftarrow \quad HCN + OH^-$

before reaction

$C + - \quad^\to _\leftarrow \quad - + \ -$

after reaction

$C(1-h) + - \quad^\to _\leftarrow \quad Ch + Ch$

$K_h = \dfrac{[Ch][Ch]}{[C(1-h)]}$

Let 'h << 1

So, $K_h = \dfrac{C^2 h ^2}{C}$

$K_h = Ch^2$

We know that for a salt of weak acid and strong base;

$K_h =\dfrac{K_w}{K_a} =\dfrac{1×10^{-14}}{7×10^{-10}} = 1.43×10^{-5}$

$Ch^2 = 1.43×10^{-5}$

$0.1h^2 = 1.43×10^{-5}$

$h^2 = 1.43×10^{-4}$

h = 0.012