Question

A rock salt (NaCl), ice, and water mixture is used to cool milk and cream to make homemade ice cream. How many grams of rock salt must be added to water to lower the freezing point 16.6°C?

Answer 1

To solve the amount of rock salt to be added to water to lower the freezing point, we use the formula of the colligative property called the freezing point depression.

ΔT = kmi

where k is the freezing point constant of water, m is the molality of the solute in the solution and i is the vant hoff factor for this case is equal to 2

16.6 = 1.86 (2) m
m = 4.46 mol NaCl / kg solution