What Is the Mass Percent Concentration of CaCl₂ in the Solution?

[blueskadoo42]

% by mass concentration

Homework Statement

An aqueous CaCL2 solution has a vapor pressure of 80.8mmHG at 50 degree 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

% by mass = mass solute/mass solution.

The Attempt at a Solution

I tried converting the pressure into moles then dividing the moles of CaCl2 by the total moles. I am pretty stuck..

Thanks
Skadoo!

 

[Borek]

Do you know Raoult's law?

 

[blueskadoo42]

yeah i do. p = pa*xa+pb*xb correct? not sure how to solve for the x's...

 

[Borek]

xa+xb=1

 

[blueskadoo42]

alright knowing this, i use 'a' as the vap press for cacl2 and 'b' for vap press of water? then use molecular weights to to solve for total mass of solution..?

 

[Borek]

Sounds OK. Don't forget CaCl₂ is dissociated.

 

[blueskadoo42]

ah right, almost forgot. Ill give this a run thanks.