Question

Calculate the $H^{+}$ ion concentration of a 0.01 N weak monobasic acid. The value of dissociation constant is $4.0\times {10}^{-10}$.

• A. $2\times {10}^{-6}mole{L}^{-1}$
• B. $2\times {10}^{-5}mole{L}^{-1}$
• C. $3\times {10}^{-6}mole{L}^{-1}$
• D. $3\times {10}^{-5}mole{L}^{-1}$

Answer 1

The correct option is A $2\times {10}^{-6}mole{L}^{-1}$

$HA\rightleftharpoons H^{+}+A^{-}$
Applying Ostwald's dilution law
$\alpha =\sqrt{K_{\alpha }\times V}:K_{\alpha }=4.0\times {10}^{-10}$
$V=\frac{1}{0.01}=100litre\alpha =\sqrt{4\times {10}^{-10}\times {10}^2}=2\times {10}^{-4}$
$\text{Concentration of}{H}^{+}=\frac{\alpha }{V}=\frac{2\times {10}^{-4}}{100}=2\times {10}^{-6}mole{L}^{-1}$