# Colligative properties: vapor pressure with an electrolyte

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.