Question

Calculate the pH of a 0.10 M solution of sodium phosphate.

Short answer

Answer

pH of the given solution comes out to be 10.66.

Step-by-step solution

 Calculation of Ka for Hydrolysis

Species present are Na⁺, PO₄^3- and H₂O. Na+ does not undergo hydrolysis.

Reaction involved:

$$\begin{gathered} P{O}_{4\left(aq\right)}^{3-}+H_{2}O\iff HP{O}_{4\left(aq\right)}^{2-}+O{H^{-}}_{\left(aq\right)} \\ {H}_{2}O+H_{2}O\iff H_3{O^{+}}_{\left(aq\right)}+O{H}_{\left(aq\right)}^{-} \\ {K}_w={10}^{-14} \end{gathered}$$

K_b can be calculated as

data-custom-editor="chemistry" ${\mathrm{K}}_{\mathrm{w}}=\frac{\left[{\mathrm{K}}_{\mathrm{w}}\right]}{\left[{\mathrm{K}}_{\mathrm{w}}\right]}=\frac{1\times {10}^{-14}}{4.8\times {10}^{-13}}=2.08\times {10}^{-2}$