Question

If 0.860 mol of a nonvolatile nonelectrolyte are dissolved in 3.30 mol of water, what is the vapor pressure PH₂O of the resulting solution? The vapor pressure of pure water is 23.8 torr at 25 C .

Answer 1

The vapor pressure of the solution, calculated using Raoult's Law and the mole fraction of water, is approximately 18.9 torr.

Step-by-step explanation:

To find the vapor pressure of a solution, we use Raoult's Law which states that the vapor pressure of a solvent in a solution (PH2O) is equal to the mole fraction of the solvent (XH2O) multiplied by the vapor pressure of the pure solvent (P°H2O). The mole fraction is calculated by dividing the moles of solvent by the total moles of solvent plus solute. Given we have 0.860 mol of solute dissolved in 3.30 mol of water, the mole fraction of water is:

XH2O = moles of H2O / (moles of H2O + moles of solute)

XH2O = 3.30 / (3.30 + 0.860) = 3.30 / 4.16

XH2O = 0.7933 (approx)

We then apply Raoult's Law to find the vapor pressure of the solution:

PH2O = (XH2O) (P°H2O)

PH2O = (0.7933) (23.8 torr)

PH2O = 18.899 torr (approx)

The vapor pressure of the resulting solution is approximately 18.9 torr.