The \( K_{2} \) expression for the \( \mathrm{H}_{2} \mathrm{PO}_{4}^{-} / \mathrm{HPO}_{4}^{2-} \) buffer is given by the equation What is the \( \mathrm{pH} \) of a 3:2 mixture of \( \mathrm{H}_{2}