Question

A sample of a mixture of $CaC{l}_2$ and $N{a}_{2}C{O}_3$ weighing $4.22$ g was treated to precipitate all the $Ca$ as $CaC{O}_3$. This $CaC{O}_3$ is heated and quantitatively converted into $0.959$ g of $CaO$. Calculate the percentage of $CaC{l}_2$ in the mixture.

(Atomic mass of $Ca=40,O=16,C=12$ and $Cl=35.5g/mole)$

• A. $55.28$ %
• B. $37.3$ %
• C. $45.00$ %
• D. $49.01$ %

Answer 1

The correct option is C $45.00$ %

$CaC{O}_3\to CaO+C{O}_2$
The molar masses of $CaC{O}_3$ and $CaO$
are 100 and 56 g/mol respectively.
100 g of $CaC{O}_3$ will give 56 g of $CaO$
0.959 g $CaO$ corresponds to $\frac{0.959\times 100}{56}=1.72$ g of $CaC{O}_3$
The molar mass of $CaC{l}_2$ is 111 g/mol.
1.72 g of $CaC{O}_3$ corresponds to $\frac{1.72\times 111}{100}=1.9$ g of
$CaC{l}_2$
The percent of $CaC{l}_2$ in sample is $\frac{1.9\times 100}{4.22}=45.00$ %