Question

$1.64$ g of a mixture of $CaC{O}_3$ and $MgC{O}_3$ was dissolved in $50$ mL of $0.8MHCl$. The excess of acid required $16$ mL of $0.25MNaOH$ for neutralization. Calculate the percentage of $CaC{O}_3$ in the sample.

• A. $51\%$
• B. $75\%$
• C. $49\%$
• D. $25\%$

Answer 1

Answer: (C)

$49\%$

The balanced reaction is as follows:
$CaC{O}_3+2HCl\to CaC{l}_2+H_{2}O+C{O}_2$
$x$ $2x$
$MgC{O}_3+2HCl\to MgC{l}_2+H_{2}O+C{O}_2$
$y$ $2y$
$2x+2y=\frac{(50\times 0.8-16\times 0.25)}{1000}\Rightarrow x+y=0.018$.......(1)
$x\times 100+y\times 84=1.64$ ........(2)

$\%CaC{O}_3=\frac{x\times 100}{1.64}\times 100=48.78\%$

$\%MC{O}_3=52.22\%$