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.

 

[Blueshift5]

No problem, let me help you understand how an electrolyte affects vapor pressure in a solution. Colligative properties, such as vapor pressure, are dependent on the number of particles present in a solution, rather than the type of particles. In the case of an electrolyte, it dissociates into ions when dissolved in a solution. This means that one particle of electrolyte can actually produce multiple ions in the solution.

Now, let's look at Raoult's law, which states that the vapor pressure of a solution is equal to the mole fraction of the solvent multiplied by the vapor pressure of the pure solvent. In the case of an electrolyte solution, the presence of ions will decrease the mole fraction of the solvent, thus lowering the vapor pressure of the solution.

The formula you mentioned, P1=iX1P1o, is a variation of Raoult's law where i represents the van't Hoff factor, which takes into account the dissociation of electrolytes. It is important to note that the van't Hoff factor is always greater than 1 for electrolyte solutions, indicating a decrease in vapor pressure compared to a non-electrolyte solution with the same concentration.

In summary, the presence of an electrolyte in a solution will decrease the vapor pressure due to the dissociation of ions, as predicted by Raoult's law. I hope this helps clarify the concept for you.