Question

$10$ mL of a blood sample (containing calcium oxalate) is dissolved in acid. It required $20$ mL of $0.001MKMn{O}_4$ (which oxidises oxalate to carbon dioxide). Hence, $C{a}^{2+}$ ion in $10$ mL blood is :

• A. $0.200$ g
• B. $0.02$ g
• C. $2.00$ g
• D. $0.002$ g

Answer 1

The correct option is D $0.002$ g

The redox reaction is as shown below:
$5{C_2{O}_4}^{2-}+2{Mn{O}_4}^{-}\to 10C{O}_2+2M{n}^{2+}$
$1$ mole of calcium ion is equivalent to $1$ mole of oxalate ion.
The number of moles of permanganate ion $=0.020$ L $\times 0.001M=2\times {10}^{-5}$ mol.
The number of moles of oxalate ion is $\frac{5}{2}\times 2\times {10}^{-5}=5\times {10}^{-5}$
This is also equal to the number of moles of calcium ion.
The mass of calcium ion $=40\times 5\times {10}^5=0.002$ g