A solution is made by dissolving 46.5g of urea, (CH4N2O) a nonelectrolyte, in 316g of water. Calculate the vapour pressure of this solution at 40 oC. (ans in torr, note the vapour pressure of pure water at 40 oC is 55.3 torr.)
I have been struggling with this equation for over three hours and i keep getting it wrong.. Please help!!!
I finally got it right..
To calculate the vapor pressure of the solution at 40°C, we can use Raoult's law, which states that the vapor pressure of a solution is directly proportional to the mole fraction of the solvent present.
First, let's calculate the mole fraction of urea in the solution.
Step 1: Calculate the moles of urea.
Molar mass of urea (CH4N2O) = 60.06 g/mol
moles of urea = mass / molar mass = 46.5 g / 60.06 g/mol = 0.774 mol
Step 2: Calculate the moles of water.
Molar mass of water (H2O) = 18.02 g/mol
moles of water = mass / molar mass = 316 g / 18.02 g/mol = 17.53 mol
Step 3: Calculate the mole fraction of urea.
mole fraction of urea = moles of urea / total moles = 0.774 mol / (0.774 mol + 17.53 mol) = 0.0424
Now that we have the mole fraction of urea, we can calculate the vapor pressure of the solution using Raoult's law.
vapor pressure of solution = mole fraction of solvent * vapor pressure of pure solvent
The vapor pressure of pure water at 40°C is given as 55.3 torr.
vapor pressure of solution = (1 - mole fraction of urea) * vapor pressure of pure water
= (1 - 0.0424) * 55.3 torr
= 0.9576 * 55.3 torr
= 52.9 torr (rounded to one decimal place)
Therefore, the vapor pressure of the solution at 40°C is approximately 52.9 torr.