0.1 moles/lit of a weak acid solution contains 0.001 moles/lit of the conjugate base ($$\text{B}^-$$).<br>a) What is the dissociation constant ($$K_a$$) of the acid?<br>b) Calculate the pH of 0.1 M solution of weak acid (AH)?<br>c) This acid is neutralized by adding required quantity of aqueous NaOH solution. What is the approximate the range of pH of solution?<br>d) To the original solution HCl is added. What happens to the ratio of conjugate base to the acid and how $$K_a$$ of the acid is affected?<br>e) To the above original solution sodium salt of same weak acid is added. What happens to the pH of the solution?

PLACEHOLDER ANSWER - the question has five parts. a) $$[\text{H}^+] = [\text{B}^-] = 10^{-3}$$, so $$K_a = \frac{10^{-3} \times 10^{-3}}{0.1} = 10^{-5}$$. b) $$\text{pH} = -\log 10^{-3} = 3$$. c) The salt of a weak acid and a strong base hydrolyses to give a basic solution, so the pH is a little above 7, roughly 8 to 9 (about 8.85 for a 0.05 M salt solution). d) HCl supplies the common ion $$\text{H}^+$$, which suppresses ionisation, so the ratio $$\frac{[\text{B}^-]}{[\text{HA}]}$$ decreases, but $$K_a$$ is unchanged since it depends only on temperature. e) Adding $$\text{B}^-$$ suppresses the acid's ionisation and forms a buffer, so $$[\text{H}^+]$$ falls and the pH increases.