We’re being asked to calculate the mass of Ca3(PO4)2 needed to achieve the freezing point of the solution as the one given with sucrose.
Recall that the freezing point of a solution is lower than that of the pure solvent and the change in freezing point (ΔTf) is given by:
The change in freezing point is also related to the molality of the solution:
i = van’t Hoff factor
m = molality of the solution (in m or mol/kg)
Kf = freezing point depression constant (in ˚C/m) of the solvent
We go through the following steps to solve the problem:
Step 1. Calculate the molality of the solution
Step 2. Calculate the moles of the solute
Step 3. Calculate the mass of the solute
A solution is prepared by dissolving 456 g of sucrose (C12H22O11, molar mass 342 g/mol) in 764 g of water (18.02 g/mol; density 1.00 g/mL) calculate:
d) How many grams of Ca 3 (PO4)2 must be added to 764g of water to have the same effect?