Question

The calcium oxalate isolated from blood is dissolved in acid and titrated against a standardised $KMn{O}_4$ solution. In one test, it is found that the calcium oxalate isolated from a $10.0$ mL sample of blood requires $24.2$ mL of $9.56\times {10}^{-4}$ M $KMn{O}_4$ for titration. The number of milligrams of calcium per mL of blood as $y\times {10}^{-2}$, then y is :

Answer 1

$2$ moles $KMn{O}_4$ gives $5$ moles $Ca{C}_2{O}_4$
Molar mass of calcium oxalate $=128$ g/mol.

Number of moles of $KMn{O}_4=\frac{24.2}{1000}\times 9.56\times {10}^{-4}M=2.33\times {10}^{-5}$ moles

Number of moles of $C{a}_2{C}_2{O}_4=\frac{5}{2}\times 2.33\times {10}^{-5}$ moles $=5.8\times {10}^{-5}$ moles

Mass of $Ca{C}_2{O}_4=5.8\times {10}^{-5}$ moles $\times 128=0.007403$ g $=7.4$ mg

Mass of calcium oxalate in one ml of blood $=\frac{7.4mg}{10.0mL}=0.74mg/mL=74\times {10}^{-2}mg/mL$

Hence, the value of $y$ is $74$.