Question

A $10\text{g}$ of a mixture of calcium chloride and sodium chloride is treated with $N{a}_{2}C{O}_3$ to precipitate calcium as calcium carbonate. This $CaC{O}_3$ is heated to convert all the calcium to $CaO$ and the final mass of $CaO$ is $1.12\text{g}$. Calculate $\%$ by mass of $NaCl$ in the original mixture.

• A. $76\%$
• B. $79\%$
• C. $78\%$
• D. $77.4\%$

Answer 1

The correct option is D $77.4\%$

Mass of $CaC{l}_2-x\text{gm}$
Mass of $NaCl-y\text{gm}x+y=10$
$CaC{l}_2+N{a}_{2}C{O}_3\to CaC{O}_3+2NaCl$
$CaC{O}_3\stackrel{\Delta }{\to }CaO+C{O}_2$
56 g of CaO is obtained from 100 g of calcium carbonate
Let, $a$ be the mass of $CaC{O}_3$
$\frac{a}{100}\times 56=1.12\Rightarrow a=2\text{g}$
1.12 g of CaO is obtained from 2 g of calcium carbonate

100 g of calcium carbonate is obtained from 113 g of calcium chloride

$\frac{x}{113}\times 100=2\text{g}$
$x=2.26\text{g}$

2 g is obtained from 2.26 g of calcium chloride
Hence mass of sodium chloride = 10 -2.226 = 7.74 g
$\therefore \%$ by wt. of $NaCl=\frac{7.78}{10}\times 100=77.4\%$