The $pK_a$ of an equimolar mixture of sodium acetate and acetic acid is $4.74$. What is the $pH$ of the solution?

Calculate the $pH$ of a buffer solution prepared by mixing $30 \ mL$ of $0.1 \ M$ $NaOH$ and $100 \ mL$ of $0.1 \ M$ $CH_3COOH$. (Given: $pK_a$ of $CH_3COOH = 4.76$)

Which among the following pairs constitutes a buffer?

$0.1 \ M$ formic acid solution is titrated against $0.1 \ M \ NaOH$ solution. What would be the difference in $pH$ between $1/5$ and $4/5$ stages of neutralization of acid?

$20 \ mL$ of $0.1 \ M \ H_2SO_4$ is added to $30 \ mL$ of $0.2 \ M \ NH_4OH$ solution. The $pH$ of the resultant mixture is [$pK_b$ of $NH_4OH = 4.7$].

Find the $pH$ of a buffer solution prepared by mixing $300 \, mL$ of $0.3 \, M \, NH_3$ and $500 \, mL$ of $0.5 \, M \, NH_4Cl$. Given $K_b$ for $NH_3 = 1.8 \times 10^{-5}$.