Problem: An aqueous CaCl2 solution has a vapor pressure of 106.4 mmHg at 55.0 oC. The vapor pressure of pure water at this temperature is 118.0 mmHg. What is the concentration of CaCl2 in mass percent?A. 40.2%B. 25.3%C. 18.3%D. 15.3%E. 21.2%

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We’re being asked to determine the mass percent of CaCl2 in solution. Recall that the mass percent of a solution is given by:



We’re given the vapor pressure of the solution, 106.4 mmHg, and the vapor pressure of pure water, 118.0 mmHg. The vapor pressure of a solution can be given by Raoult’s Law:



where P˚ = vapor pressure of solvent and χ = mole fraction of solvent. This means that for this solution:



The mole fraction of H2O is:



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Problem Details

An aqueous CaCl2 solution has a vapor pressure of 106.4 mmHg at 55.0 oC. The vapor pressure of pure water at this temperature is 118.0 mmHg. What is the concentration of CaCl2 in mass percent?

A. 40.2%
B. 25.3%
C. 18.3%
D. 15.3%
E. 21.2%

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