Question

The freezing point is propertie of colligative characterized by lowering of the freezing point of a liquid in the presence of a non-volatile solute. The cryoscopic lowering a, Δ t, is expressed by:
ΔT = kcM
where KC is the cryoscopic constant and M is the total molality of the solution species.
Consider aqueous solutions and concentrations 5,0x10-3 mol.kg -1 with fully dissociated solutes: potassium nitrate (KNO3), calcium chloride (CaCl2), cadmium nitrate ((Cd (NO3) 2), ferric chloride ( FeCl 3) and aluminum nitrate (Al (NO3) 3).
The solution s to present the lowest freezing point depression is the
a) potassium nitrate.
b) calcium chloride.
c) cadmium nitrate.
d) ferric chloride.
e) aluminum nitrate.

Answer 1

Colligative properties:

The properties of solution which depends only on the concentration of solute particle are known as colligative properties. General meaning of colligative properties is “counting”, then we can say that the colligative properties of solution is depends on the counting particles of solutes.

Types of colligative properties:

There are four important colligavtive properties which are following:

1.   Vapor pressure depression.

2.   Boiling point elevation.

3.   Freezing point depression.

4.   Osmotic pressure.

Hence aluminum nitrate and ferric chloride ( FeCl 3) show lowest freezing point depression due to high vanhoff factor or it give 4 ions.

        Compound                                 number of ions

potassium nitrate (KNO3),                          2

calcium chloride (CaCl2),                              3

cadmium nitrate ((Cd (NO3) 2),                                 3

ferric chloride ( FeCl 3) and                          4

aluminum nitrate (Al (NO3) 3).                  4