Question

Use the van't Hoff factors in the table below to calculate each colligative property.

Table. Van't Hoff Factors at 0.05 m Concentration in Aqueous Solution

Solute	i Expected	i Measured
Nonelectrolyte	1	1
{\rm NaCl}	2	1.9
{\rm MgSO_4}	2	1.3
{\rm MgCl_2}	3	2.7
{\rm K_2SO_4}	3	2.6
{\rm FeCl_3}	4	3.4

Part A:

What is the melting point of a 6.00×10⁻²m iron(III) chloride solution?

Part B:

What is the osmotic pressure of a 0.077 {\rm \; {\rm M}} potassium sulfate solution at 298 {\rm K} ?

Part C:

What is the boiling point of a 1.09 {\rm \,\%} by mass magnesium chloride solution?

Answer 1

T = i*m*kf

    FeCl3 ----> Fe⁺³ + 3Cl^-

i = 4

T = i*m*kf

      = 4*0.06*1.86

    = 0.4464C⁰

part-B

pi = CRT

    = 0.077*0.0821*298

   = 1.884 atm

part-C

1.09% MgCl2 means 1.09gm of MgCl2 present in 100gm of water

molality = 1.09*1000/95.2*100

             = 0.1144m

T = i*m*kb

      = 3*0.1144*0.52

    = 0.1784C

boiling point is 100+0.1784 =100.1784C⁰