Question

A solution contains 5.00 g of urea, CO(NH2)2 , a nonvolatile compound, dissolved in 0.100 kg of water. If the vapor pressure of pure water at 25ºC is 23.7 mm Hg, what is the vapor pressure of water over the solution? (MM of urea = 60.06 g/mol)

Answer 1

the vapor pressure of water over the solution is 23.3445 mm Hg

Step-by-step explanation:

From Raoult's law:

`P_(solution) = x_(solvent) * P^0_(solvent)`

where:

`P_(solution)` is the observed pressure above the solution

`x_(solvent)` is the molar fraction of solvent (here water)

`P^0_(solvent)` is the vapor pressure of pure solvent at a given temperature

Moles of urea = (5 g)/(60.06 g/mol) = 0.083 mol

Moles of water = (100 g)/(18 g/mol) = 5.556 mol

Mole fraction of water = 5.556/(5.556 + 0.083) = 0.985

Therefore:

`P_(solution) = 0.985 * 23.7 \;mm\;Hg`

`P_(solution) = 23.3445 \;mm\;Hg`