Chapter 7, Problem 7.103SP

Calcium levels in blood can be determined by adding oxalate ion to precipitate calcium oxalate, CaC₂O₄, followed by dissolving the precipitate in aqueous acid and titrating the resulting oxalic acid (H₂C₂O₄) with KMnO₄:

$\begin{array}{l}\text{5}{\text{H}}_{\text{2}}{\text{C}}_{\text{2}}{\text{O}}_{\text{4}}(aq)+\text{2}{\text{MnO}}_{\text{4}}{}^{-}\text{(}aq\text{)}+\text{6}{\text{H}}^{+}\text{(}aq\text{)}\stackrel{}{\to }\\ \text{1}0{\text{CO}}_{\text{2}}\text{(}g\text{)}+\text{2}{\text{Mn}}^{\text{2}+}\text{(}aq\text{)}+\text{8}{\text{H}}_{\text{2}}\text{O(}l\text{)}\end{array}$

How many milligrams of Ca²⁺ are present in 10.0 mL of blood if 21.08 mL of 0.000 988 M KMnO₄ solution is needed for the titration?