A 10.0 g sample of a mixture of calcium chloride and sodium chloride is treated with Na2CO3 to precipitate the calcium as calcium carbonate. This CaCO3 is heated to convert all the calcium to CaO and the final mass of CaO is 1.62 gms. The % by mass of CaCl2 in the original mixture is:
Correct answer: B. 32.1%
- A. 15.2%
- B. 32.1%
- C. 21.8%
- D. 11.07%
Explanation
The problem involves determining the percentage by mass of CaCl2 in a mixture. First, calculate the moles of CaO formed by dividing the mass of CaO (1.62 g) by its molar mass (56.08 g/mol), resulting in 0.0289 moles. Since the conversion of CaCO3 to CaO is a 1:1 process, these moles represent the moles of CaCl2 in the original mixture. Multiply these moles by the molar mass of CaCl2 (110.98 g/mol) to find the mass of CaCl2, which is 3.21 g. The percentage by mass is then calculated by dividing the mass of CaCl2 by the total mass of the mixture (10.0 g) and multiplying by 100, yielding approximately 32.1%. Other options do not follow the correct stoichiometric calculations, leading to incorrect percentages.
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