Ionic Equilibrium

${\left( {HS{O_4}} \right)^ - }\,\,\,$ can accept and donate a proton

${\left( {HS{O_4}} \right)^ - } + {H^ + } \to {H_2}S{O_4}\,\,\,$ (acting as base)

${\left( {HS{O_4}} \right)^ - } - {H^ + } \to {H_2}S{O_4}^{2 - }.\,\,\,$ (acting as acid)

$Mg{\left( {OH} \right)_2} \to \mathop {\left[ {M{g^{2 + }}} \right]}\limits_x + 2\mathop {\left[ {O{H^ - }} \right]}\limits_{2x} $

${K_{sp}} = \left[ {Mg} \right]{\left[ {OH} \right]^2}$

$ = \left[ x \right]{\left[ {2x} \right]^2}$

$ = x.4{x^2} = 4{x^3}.$

NOTE : A buffer is a solution of weak acid and its salt with strong base and vice versa.

$HCL$ is strong acid and $NaCL$ is its salt with strong base.

$pH$ is less than $7$ due to $HCL$.