Question

1. The normal temperature range of the liquid phase of pure water is 0°C (freezing point) to 100°C (boiling point). Which of the following solutions will have the largest temperature range for the liquid state?
   1. 0.1 m aqueous potassium chloride solution
   2. 0.1 m aqueous sodium chloride solution       
   3. 0.1 m aqueous calcium chloride solution
   4. 0.1 m aqueous methanol solution

Answer 1

Answer:

Elevation in boiling point is

∆Tb= i x Kb x m

Where i=Van't Hoff factor, Kb=boiling point constant, m=molality.

Depression in freezing point is

∆Tf=i x Kf x m

Here Kf=freezing point constant.

In the given options, molality of all solutions is 0.1 m and Kb and Kf are constants.

Therefore ∆Tb and ∆Tf is dependent on the Van't Hoff factor.

i=2 for KCl and NaCl

KCl -----> K^+ + Cl^-

NaCl ------> Na^+ + Cl^-

i=3 for CaCl2,

CaCl2 --------> Ca^+2 + 2Cl^-

Methanol is a non electrolyte ,then i=1

Largest temperature range solution has large value of i.

Therefore (c) 0.1 m aqueous CaCl2 solution have largest temperature range.

Please let me know if you have any doubt. Thanks