Answer:
49.8 Torr will be the vapor pressure of the solution
Explanation:
Vapor pressure lowerig is the colligative property that must be applied to solve this. The formula is: ΔP = P° . Xm . i
where ΔP = P° (vapor pressure of pure solvent) - Vapor pressure of solution (P')
Xm, the mole fraction of solute (moles of solute / total moles)
i = Van't Hoff factor (numbers of ions dissolved in the solution)
The solute, potassium phosphate dissociates like this:
K₃PO₄ → 3K⁺ + PO₄³⁻ so we have 3 moles of cation K⁺ and 1 mol of phosphate. Therefore, we have 4 moles of ions, is we assume that the solute completely dissociates → i = 4
Let's find out the mole fraction for solute (Xm)
Xm = mol of solute / Total moles
where total moles = mole of solute + moles of solvent
0.159 mol + 0.941 mol = 1.1 moles
Xm = 0.159 / 1.1 → 0.144
Let's replace the data in the formula
P° - P'= P° . Xm . i
118.1 Torr - P' = 118.1 Torr . 0.144 . 4
P' = - (118.1 Torr . 0.144 . 4 - 118.1 Torr)
Vapor pressure for solution is : 49.8 Torr
