# Homework Help: The Van't hoff factor for CaCL2 is 2.71

1. Jul 21, 2014

### Jef123

1. The van't hoff factor for CaCL2 is 2.71. What is its mass % in aqueous solution that has Tf = -1.14°C

3. The attempt at a solution

So I think I am suppose to use the change in freezing point equation: ΔTf= kfmi. Where kf = is the molal freezing point depression constant, i = van't hoff factor, m = molal concentration.

Other than that, I am kind of lost. It seems like there is not enough variables given. Any suggestions?

2. Jul 22, 2014

### epenguin

Congratulations for giving full information on the problem, which often we have to ask after. Often actually setting out the information gives the answer.

In this case you give a relation between four quantities, and three of the quantities are given. So the first step is to get the fourth from that.

From that result you have to get the mass %. Be explicit about what your definition of this is.

(I suppose this is the point of the exercise which is somewhat artificial IMO.
Apart from the fact I don't know how well regarded and used Van't Hoff's i is these days.)

3. Jul 26, 2014

### Teemo

Water's freezing point depression constant is 1.86 degrees Celsius/molal.