Vapor Pressure of Solutions

In summary, to find the concentration of CaCl2 in mass percent in an aqueous solution, you can use Raoult's Law and the definition of molar fraction. Assuming 1L of the solution and a density of 1 g/mL, you can set up a set of equations to solve for the mass of solute and solvent, which can be used to calculate the mass percent of CaCl2 in the solution.
  • #1
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Homework Statement



An aqueous CaCl2 solution has a vapor pressure of 82.3 mmHg at 50 degrees C. The vapor pressure of pure water at this temperature is 92.6 mmHg. What is the concentration of CaCl2 in mass percent?


Homework Equations


mass %=(mass of component/total mass)*100%
Psolution=XH2OPH2O


The Attempt at a Solution


I know I have to use Raoult's Law in order to compute the mole fraction but I'm not sure what to do after. Once I have mole fraction what do I do?
 
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  • #2
Assume 1L of the solution. Molar fraction of CaCl2 is x, molar fraction of water is 1-x. Write definition of molar fraction, write how does the mass depend on number of moles for solvent and for solute. Mass of solvent plus mass of solute is a mass of 1L of solution. Assume density of 1 g/mL. That will give you a set of equations, you should be able to solve them for mass of solute and mass of solvent.
 

1. What is the definition of vapor pressure?

Vapor pressure is the pressure exerted by the vapor of a substance in equilibrium with its liquid or solid phase at a given temperature.

2. How does adding solutes affect the vapor pressure of a solution?

Adding solutes to a solution lowers the vapor pressure of the solution compared to the pure solvent. This is because the solute particles occupy space at the surface of the solution, reducing the number of solvent molecules that can escape into the vapor phase.

3. What is Raoult's law and how is it related to vapor pressure of solutions?

Raoult's law states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent in the solution. This means that as the mole fraction of the solvent decreases, the vapor pressure of the solution also decreases.

4. How does temperature affect the vapor pressure of solutions?

As temperature increases, the vapor pressure of a solution also increases. This is because at higher temperatures, the molecules in the solution have more kinetic energy and are more likely to escape into the vapor phase.

5. Can the vapor pressure of a solution ever be higher than the vapor pressure of the pure solvent?

No, the vapor pressure of a solution can never be higher than the vapor pressure of the pure solvent. This is because the presence of solute particles will always lower the vapor pressure of the solution compared to the pure solvent.

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