Question

A 10.0 g sample of a mixture of calcium chloride and sodium chloride is treated with $N{a}_{2}C{O}_3$ to precipitate the calcium as calcium carbonate. This $CaC{O}_3$ is heated to convert all the calcium to CaO and the final mass of CaO is 1.62 gms. The % by mass of $CaC{l}_2$ 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 $CaC{l}_2=\frac{1.62}{56}$ 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 $CaC{l}_2=\frac{3.21}{10}\times 100=32.1\%$