[darklurker002]

Hi, I have these four questions here that are a bit tricky~
I tried doing them, but im really having a lot of trouble. would you mind helping me?

Thanks a bunch!!!



1. Concentration - Calculate the molarity and mole fraction of chloroform in a 2.00m solution of chloroform (CHCl₃) in benzene (C₆H₆). The density of chloroform = 1.48 g/cm^3; the density of benzene = 0.876 g/cm^3. Assume that the volumes are additive.

I got 1.752 for the Molarity, and 0.9936 for the mole fraction of CHCL₃. I am not sure If I am supposed to use 1L.  Can you please show me the correct way of solving this problem?

2. Raoul's Law - An aqueous solution of NaCl has a vapor pressure of 18.4 Torr at 25 degrees Celcius. What is the mole fraction of Na+ in this solution? What would the vapor pressure of the solution be at 40 degrees celcius? Vapor pressure of water = 23.8 Torr at 25 degrees Celcius and 55.3 Torr at 40 degrees Celcius.

I got 0.46128 for the mole fraction of Na+, I have no idea how to get the second part of this problem. I'm stuck!
 
3. Volatile solvents - A solution is prepared by mixing 0.0500 mol CH₂Cl₂ with 0.0200 mol CH₂Br₂ at 25 degrees Celcius. Assumng ideal behavior find the total vapor pressure of the solution and the mole fraction of CH₂Cl₂ in the vapor phase. The vapor pressure of pure CH₂Cl₂ and CH₂Br₂ are 133 Torr and 11.4 Torr, respectively.

i dont understand what the mole fractions would be. would this be like calculating the vapor pressure of a solution with two liquids... so using a modification of Raoul's law?

4. Osmotic pressure - A 1.00L solution made from 25.00g of an unknown molecular compound has an osmotic pressure of 0.145 atm at 27.0 degrees Celcius. What is the molar mass of the compound?

I tried this problem but im not sure how I can even start it. Can anyone help? :1eye:


Thanks for helping me~

[DrCMS]

Q 1.  
2m (molality) = 2 moles / kg of solvent

molarity M = moles / L of solution

mole fraction of x = moles of x / total moles


Q 2. and 3.
Raoult's law.
The vapor pressure of a solvent in an ideal solution equals the mole fraction of the solvent times the vapor pressure of the pure solvent.

Q 4.
Osmotic pressure = molarity x R' x T      (R'= 0.0821 L atm/K  so T must be in Kelvin)