Question

A $10.0\, g$ sample of a mixture of calcium chloride and sodium chloride is treated with $Na_{2}CO_{3}$ to precipitate the calcium as calcium carbonate. This $CaCO_{3}$ is heated to convert all the calcium to $CaO$ and the final mass of $CaO$ is $1.62\, gms$. The $\%$ by mass of $CaCl_{2}$ in the original mixture is

• A. 15.2%
• B. 32.1%
• C. 21.8%
• D. 11.07%

Answer 1

Answer: (B)

Moles $=\frac{\text { Weight in gm }}{\text { Molecular weight }}$
Moles of $CaO =\frac{1.62}{56}$
Moles of $C a C l_{2}=\frac{1.62}{56}$
Mass of $CaCl _{2}=\frac{1.62}{56} \times 111=3.21\, gm$
Mass $\%$ of $C a C l_{2}=\frac{3.21}{10} \times 100=32.1 \%$