The $pH$ of a buffer solution obtained by mixing $50 \ mL$ of $0.1 \ M$ $NH_4OH$ and $25 \ mL$ of $2.0 \ M$ $NH_4Cl$ is ($pK_b$ of $NH_4OH$ is $4.8$).

In a mixture of a weak acid and its salt,the ratio of concentration of acid to salt is increased ten-fold. The $pH$ of the solution

$20$ mL of a solution of acetic acid required $28.4$ mL of $0.1$ $M$ NaOH for its neutralization. $A$ solution $(X)$ was prepared by mixing $20$ mL of the above acetic acid and $14.2$ mL of $0.1$ $M$ NaOH solution. What is the pH of the solution $(X)$? ($pK_a$ value of acetic acid is $4.75$).

Derive the Henderson-Hasselbalch equation.

$A$ solution of $0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ and $0.08 \ mol$ of $HCl$ is diluted to $1 \ L$. The $pOH$ of the resulting solution is $(\log 1.25 = 0.1)$.

The $pKa$ of a weak acid $HA$ is $4.5$. The $pOH$ of an aqueous buffer solution in which the acid $HA$ is $50\%$ ionized is: