Calculate the amount of $(NH_4)_2SO_4$ in grams which must be added to $500 \ mL$ of $0.200 \ M \ NH_3$ to yield a solution with $pH = 9.35$ ($K_b$ for $NH_3 = 1.78 \times 10^{-5}$).

Find $pH$ of the resultant solution formed by the addition of $500 \ mL$ $0.1 \ M$ $Ba(OH)_2$ and $500 \ mL$ $0.6 \ M$ $NH_4Cl$ in $1 \ L$ pure $H_2O$ at $25 \ ^oC$ (Use $\log \ 2 = 0.3$,$\log \ 3 = 0.5$,$\log \ 5 = 0.7$,$K_b(NH_3) = 10^{-5}$)

$A$ buffer solution is prepared by mixing $0.01 \ M$ weak acid and $0.05 \ M$ solution of a salt of weak acid and strong base. What is the $pH$ of the buffer solution? $(pK_a = 4.74)$

What is $[H^{+}]$ in $mol/L$ of a solution that is $0.20\, M$ in $CH_3COONa$ and $0.10\, M$ in $CH_3COOH$? $K_a$ for $CH_3COOH = 1.8 \times 10^{-5}$.

$40 \ mL$ of $0.1 \ M$ ammonia solution is mixed with $20 \ mL$ of $0.1 \ M \ HCl$. What is the $pH$ of the mixture? ($pK_b$ of ammonia solution is $4.74$).

$A$ certain acidic solution contains equal concentrations of $X^-$ and $HX$. If $K_b$ for $X^-$ is $10^{-10}$,then the $pH$ of the buffer is equal to: