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 $\text{=} \, \frac{\text{mass } \text{in} \, \text{gram}}{\text{Molar} \text{ mass}}$
Moles of $\text{CaO} \, \text{=} \, \frac{\text{1} \text{.62}}{\text{56}}$ mol
Moles of $CaCl_{2}=\frac{1.62}{56}$ mol
Mass of $\text{CaCl}_{\text{2}} \, \text{=} \, \frac{\text{1} \text{.62}}{\text{56}} \, \times \, \text{111} \, \text{=} \, \text{3} \text{.21} \, \text{gm}$
Mass $\text{\%} \, \text{=} \, \frac{\text{Weight} \, \text{in} \, \text{gm}}{\text{Total} \, \text{weight} \, \text{given}} \, \times \, \text{100}$
Percentage of $CaCl_{2}=\frac{3.21}{10}\times 100=32.1\%$