Answer
(e) $[H^+] = 1.1 \times 10^{-5} \space M$
Work Step by Step
1. Write the equilibrium constant expression:
- The exponent of each concentration is equal to its balance coefficient.
$$K_c = \frac{[Products]}{[Reactants]} = \frac{[ H^+][ CN^- ]}{[ HCN ]}$$
2. At equilibrium, these are the concentrations of each compound:
$[ HCN ] = 0.25 \space M - x$
$[ H^+ ] = x$
$[ CN^- ] = x$
$$4.9 \times 10^{-10} = \frac{(x)(x)}{(0.25 - x)}$$
$x = 1.1 \times 10^{-5}$
3.
$[H^+] = 1.1 \times 10^{-5}$
