Calculate the $pH$ of a buffer solution containing $0.027 \ M$ weak acid and $0.054 \ M$ of its salt with a strong base,if the $pK_{a}$ is $4.2$.

$A$ buffer solution can be prepared by mixing equal volumes of

$A$ 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:

$A$ buffer solution with $pH = 9$ is prepared by mixing $NH_4Cl$ and $NH_4OH$. Calculate the number of moles of $NH_4Cl$ dissolved in $1.0 \, L$ of $1.0 \, M \, NH_4OH$ solution. (Given: $K_b(NH_4OH) = 1.8 \times 10^{-5}$)

$A$ buffer solution is prepared in which the concentration of $NH_3$ is $0.30 \ M$ and the concentration of $NH_4^+$ is $0.20 \ M.$ If the equilibrium constant,$K_b$ for $NH_3$ equals $1.8 \times 10^{-5},$ what is the $pH$ of this solution? $(\log \ 2.7 = 0.43)$

When $NaOH$ is added to a $CH_3COOH$ solution,$60\%$ of the acid is neutralized. If the $pK_a$ is $4.7$,the $pH$ of the resulting solution is: