Colligative properties: vapor pressure with an electrolyte

[Juan Pablo]

I'm trying to figure out how an electrolyte affects vapour pressure in a solution. My book (Chang chemistry) only lists the formulas for osmotic pressure, boiling point and freezing point. I guess Raoult's law would be something like:

P_{1}=i X_{1} P^{1}_{o}

Sorry for not respecting the template, it just doesn't seem appropriate for this question.

 

[Borek]

In the case of electrolyte you may just assume its vapor pressure is zero, then follow the molar fraction proportional to vapor pressure path. Don't forget Van't Hoff factor.