[jjl5098]

hey guys,
Can you guys help me answer these 2 questions about freezing point depression

1. A solution was prepared by dissolving 9.2 g of ethyl alcohol (C2H5OH) in 450g of water. At what temperature will this solution freeze?

2. A salt is known to be an alkali metal fluoride. A quick approximate freezing point determination indicates that 4g of salt dissolved in 100g of water produces a solution which freezes at about -2.8 C. what is the formula of the salt? Assume i = 2.


thanks in advance

[calciumoxide]

Hmmm, for the first question, I think you should use the freezing point depression to calculate for the change in freezing point from water to the solution. First you need to find the freezing point constant (k) for ethanol and use the freezing point depression equation = i x k x molality, i in this case is the van 't Hoff i factor (basically separable parts from a chemical compound). For ethanol, I think it's just 1.

Your second question is very similar to the first, except this time they give you the change in freezing point of water. This time you would use the same equation and solve for molality and work your way from molality to find the mass and formula.

Hope this helps!

[Borek]

First you need to find the freezing point constant (k) for ethanol

I would use constant for water.

[calciumoxide]

Good catch, absolutely right, the freezing point constant should be for the solvent. Thanks for correcting.