$20 \ mL$ of $0.1 \ (N)$ acetic acid is mixed with $10 \ mL$ of $0.1 \ (N)$ solution of $NaOH$. The $pH$ of the resulting solution is ($pK_a$ of acetic acid is $4.74$). (in $.74$)

$A$ physician wishes to prepare a buffer solution at $pH = 3.58$ that efficiently resists changes in $pH$ yet contains only small concentration of the buffering agents. Which of the following weak acids together with its sodium salt would be best to use?

$3 \; g$ of acetic acid is added to $250 \; mL$ of $0.1 \; M \; HCl$ and the solution is made up to $500 \; mL$. To $20 \; mL$ of this solution,$\frac{1}{2} \; mL$ of $5 \; M \; NaOH$ is added. The $pH$ of the solution is: [Given: $pK_{a}$ of acetic acid $= 4.75$,molar mass of acetic acid $= 60 \; g/mol$,$\log 3 = 0.4771$]. Neglect any changes in volume.

$A$ litre of buffer solution contains $0.1 \ mol$ of each of $NH_3$ and $NH_4Cl$. On the addition of $0.02 \ mol$ of $HCl$ by dissolving gaseous $HCl$,the $pH$ of the solution is found to be $...... \times 10^{-3}$ (Nearest integer).
Given: $pK_b(NH_3) = 4.745$,$\log 2 = 0.301$,$\log 3 = 0.477$,$T = 298 \ K$.

$A$ solution contains $0.1 \ mol$ of acetic acid and $0.1 \ mol$ of sodium acetate in $500 \ mL$ of solution. If the $pH$ of the solution is $4.74$,find the ionization constant $(K_a)$ of acetic acid.

$A$ buffer solution is prepared by mixing equimolar acetic acid and sodium acetate. If $K_{a}$ of acetic acid is $1.78 \times 10^{-5}$,find the $pH$ of the buffer solution.