In a buffer solution consisting ${\text{NaH}}_{\text{2}}{\text{PO}}_{\text{4}}{\text{\hspace{0.17em}and\hspace{0.17em}Na}}_{\text{2}}{\text{HPO}}_{\text{4}}$

The pH of solution can be calculated using the relation ${\text{pH\hspace{0.17em}= pK}}_{\text{2}}\text{+\hspace{0.17em}log\hspace{0.17em}}\frac{\left[{\text{HPO}}_{\text{4}}^{\text{2-}}\right]}{\left[{\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{\text{-}}\right]}$

The is acid and ${\text{NaH}}_{\text{2}}{\text{PO}}_{\text{4}}$ is salt

The pH con not be calculated

The ${\text{NaH}}_{\text{2}}{\text{PO}}_{\text{4}}$ is acid and ${\text{Na}}_{\text{2}}{\text{HPO}}_{\text{4}}$ is salt