posted by melissa .
An aqueous CaCl_2 solution has a vapor pressure of 82.1mmHg at 50C. The vapor pressure of pure water at this temperature is 92.6mmHg.
What is the concentration of CaCl_2 in mass percent?
I would approach the problem this way.
You know Psolvent = Xsolvent</sub*Posolvent. This allows you to determine Xsolvent. Now you have X for solvent and X for CaCl2. Convert those to grams and to mass percent.
Can you take it from here?