Question

What is the percent of salt in a salt solution that has freezing point of -6.7 C ? Freezing point of water 0 C

Answer 1

Data given: Depression in freezing point = Difference between the freezing point of water and that of salt solution = 6.7 degree celsius

And cryoscopic constant for water = 1.86

The depression in freezing point is related to molality of the solution by the equation

depression in freezing point = K_f molality therefore, 6.7 = 1.86 x molality

Molality = 6.7/1.86 = 3.60 mol kg^-1 of the solvent

This means in the 1 kg of water contains 3.6 mol of salt = 3.6 x58.8 g of salt(58.5 g mol^-1 is the molar mass of salt)

Thus 1 kg of water contains 210.7 g of salt

The percent of salt in the solution is therefore, 210.7x100/1000= 21.07%