[gear2d]

I was doing this problem and I am confused by 3 thing:

What is the vapor pressure of 2 m NaCl solution at 100 C (celsius)? "m" is mole fraction not moles.

Than answer for this is 709 torr:  you have 56 moles of water and 2m of Na and 2m Cl which give a mole fraction of water to be 56/60. Then times that by 760 torr (pressure where water boils at) and get 709 torr.

1) You need the mole fraction of water, so how do you know that water has 56 moles to start with?

2) Why is  it OK to take  2m NaCl and treat as 2m Na and 2m Cl? Because say it was not mole fraction but molarity, you couldn't say that 2M NaCl has 4 moles (2M of Na and 2M Cl), can you?

3) Going back to 2m NaCl -> 2m Na + 2m Cl = 4 moles total, say if you had a general salt like 3m AB2. Would you get the total moles by: 3m AB2 -> 3m A + (3m B*2)^2 = 39 moles

[Controlled Substance]

Isn't 'm' molality? mol of solute/1kg solvent

[gear2d]

Isn't 'm' molality? mol of solute/1kg solvent

You right on that part. But for some reason the solution in the back of book does the calculation by dividing the moles of water (56) by the total moles of the solution (water + NaCl = 60 moles). From that part of the explanation, I am assuming that this is moles fraction (moles of solute / total moles of solution).

[Borek]

1) You need the mole fraction of water, so how do you know that water has 56 moles to start with?

1000/18 - mass of 1L divided by molar mass.

2) Why is  it OK to take  2m NaCl and treat as 2m Na and 2m Cl? Because say it was not mole fraction but molarity, you couldn't say that 2M NaCl has 4 moles (2M of Na and 2M Cl), can you?

3) Going back to 2m NaCl -> 2m Na + 2m Cl = 4 moles total, say if you had a general salt like 3m AB2. Would you get the total moles by: 3m AB2 -> 3m A + (3m B*2)^2 = 39 moles

http://en.wikipedia.org/wiki/Van't_Hoff_Factor