Problem: 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?

FREE Expert Solution

We’re being asked to calculate the mass of Ca3(PO4)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:


ΔTf=Tf, pure solvent-Tf, solution


The change in freezing point is also related to the molality of the solution:


ΔTf=imKf


where:

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


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Problem Details

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 (PO4)must be added to 764g of water to have the same effect?