The pH of a base solution is 12.699. The amount of crystalline oxalic acid required to react with 2 lit of this base solution is (assume oxalic acid dissoiates completely)

P^OH = 14 -12.699 = 1.3

⇒ [OH^-] = 5 x10^-2

Equivalents of H₂C₂O₄ = Equivalents of base

Crystalline oxalic acid has the following formula : H₂C₂O₄. 2H₂O

 ;$$\begin{gathered} \frac{{\mathrm{W}}_{\mathrm{a}}}{\mathrm{GEW} \mathrm{of} \mathrm{acid}}={\mathrm{V}}_{\mathrm{a}}{\mathrm{N}}_{\mathrm{a}}; \\ \frac{{\mathrm{W}}_{\mathrm{a}}}{63}=2\times 5\times {10}^{-2}; \\ {\mathrm{W}}_{\mathrm{a}}=6.3 \mathrm{g} ; \end{gathered}$$