Question: How many grams of silver would have to be dissolved in 1120 g of ethanol to lower the freezing point by 0.25 degrees Celsius? Kf for ethanol is 1.99 degrees Celsius/molality.
Answer:
The equation you're looking to use is that the change in freezing point is
equal to the Kf value times the molality of the solute.
You've been given the change in temperature and the Kf.
As a result, you can solve this equation to find the molality of the resulting
solution.
In the next step, use the equation that defines molality; molality
= moles of solute/kilograms of solvent. Since you will have found the
molality in the first step and the kilograms of solvent are given to you
in the problem, finding the number of grams required shouldn't be too hard.