Question

Calculate the freezing point and boiling point in each solution, assuming complete dissociation of the solute.

1) Calculate the freezing point of a solution containing 10.6 g FeCl3 in 151 g water.

2) Calculate the boiling point of a solution above.

3) Calculate the freezing point of a solution containing 6.2% KCl by mass (in water). Express your answer using two significant figures.

4) Calculate the boiling point of a solution above

5) Calculate the freezing point of a solution containing 0.152 m MgF2

6) Calculate the boiling point of a solution above

Answer 1

Molality of solution = w/mwt*1000/wt of solvent
           
                    = (10.6/162.2)*(1000/151)

                   = 0.433 molal

i = vanhoff factor = 4

DTf = i*Kf*m

(0-x) = 4*1.86*0.433

x= freezing point of solution = -3.22 C

2) DTb = i*Kb*m

(x-100) = 4*0.512*0.433

x = boiling point of solution = 100.88 c

3)

Molality of solution = w/mwt*1000/wt of solvent
           
                    = (6.2/74.55)*(1000/93.8)

                   = 0.89 molal

i = vanhoff factor = 2

DTf = i*Kf*m

(0-x) = 2*1.86*0.89

x= freezing point of solution = -3.311 c

4) (x-100) = 2*0.512*0.89

x = boiling point of solution = 100.91 c

5) (0-x) = 3*1.86*0.152

x = freezing point of solution = -0.848 c

6) (x-100) = 3*0.512*0.152

x = boiling point of solution = 100.233 c