$20 \, mL$ of $0.2 \, M \, HCN$ is mixed with $10 \, mL$ of $0.2 \, M \, NaOH$. Calculate the $pH$ of the resulting mixture. The $pKa$ value of $HCN$ is $5$.

$0.1 \ mol$ of $CH_3NH_2$ $(K_b = 5 \times 10^{-4})$ is mixed with $0.08 \ mol$ of $HCl$ and diluted to $1 \ L$. The $[H^{+}]$ in the solution is:

Which of the following is a buffer solution?

The $pOH$ of a basic buffer (e.g.,$NH_4OH/NH_4Cl$) is $5$. If the concentration of the salt is tripled while the concentration of the base remains constant,find the new $pOH$ value. (Given: $\log 3 = 0.48$)

$A$ 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: $pK_b(NH_3) = 4.745$,$\log 2 = 0.301$,$\log 3 = 0.477$,$T = 298 \ K$.

Class $XII$ students were asked to prepare one litre of buffer solution of $pH$ $8.26$ by their chemistry teacher. The amount of ammonium chloride to be dissolved by the student in $0.2 \, M$ ammonia solution to make one litre of the buffer is $..... \, g$ (Given $pK_b(NH_3)=4.74$; Molar mass of $NH_3=17 \, g \, mol^{-1}$; Molar mass of $NH_4Cl =53.5 \, g \, mol^{-1}$)