A specific weak acid has a dissociation constant . It reacts completely with caustic soda to form th — Ionic Equilibrium Chemistry Question
Question
A specific weak acid $HX$ has a dissociation constant $K_a = 10^{-5}$. It reacts completely with caustic soda to form the salt $NaX$ at a concentration of $0.1 \text{ M}$. Calculate the exact degree of hydrolysis ($h$) of this $NaX$ solution. If the percentage hydrolysis is $z\%$, what is the exact value of $z$ multiplied by 1000? ($K_w = 10^{-14}$)
💡 Solution & Explanation
$NaX$ is a salt of a weak acid and a strong base, undergoing anionic hydrolysis. The hydrolysis constant is $K_h = \frac{K_w}{K_a} = \frac{10^{-14}}{10^{-5}} = 10^{-9}$. The degree of hydrolysis $h = \sqrt{\frac{K_h}{C}} = \sqrt{\frac{10^{-9}}{0.1}} = \sqrt{10^{-8}} = 10^{-4}$. To find the percentage hydrolysis ($z$), multiply by 100: $z = 10^{-4} \times 100 = 10^{-2}\% = 0.01\%$. Therefore, $z \times 1000 = 0.01 \times 1000 = 10$.