Solubility | Colligative Properties of Solution | Chemistry Grade XI

Solubility

Solubility | Colligative Properties of Solution | Chemistry Grade XI

Solubility | Colligative Properties of Solution

SOLUBILITY
The amount of solute in grams which can be dissolved in 100 grams of solvent to give a saturated solution at a particular temperature is called the solubility of solute at that temperature. 
 
COLLIGATIVE PROPERTIES OF SOLUTION
The colligative property of solution can be defined as the properties of solution which depends on the number of solute particles but not on a size and chemical behavior of solute. Some examples of colligative properties are:
  1. Lowering of vapour pressure
  2. Elevation of boiling point
  3. Depression of freezing point
  4. Osmotic pressure
IDEAL AND REAL SOLUTION
The solution containing non-volatile solute which neither undergoes association nor dissociation during dissolution is called an ideal solution. In an ideal solution, the number of solute particles remains constant i.e. the solute must be non-ionizable. If solute undergoes dissociation, the number of particles increases, and if solute undergoes association, number of particles decreases.

The solution containing non-volatile solute which undergoes association or dissociation during dissolution is called non-ideal solution.

VAN’T HOFF FACTOR
The association or dissociation of solute in solution, the colligative properties of solution changes, and also affects the molecular mass of the solute. So, observation of the molecular mass of solute during association becomes abnormal. This abnormality in the determination of the molecular mass of solute was first observed by Van’t Hoff factor.
 
Van’t Hoff factor is defined as the ratio of the observed value of colligative property to the theoretical value of the colligative property. It is denoted by,
     i = observed value of colligative property / theoretical value of colligative property
Colligative property is inversely proportional to molar mass.
So, i = normal stress / observed molar mass
The ratio of molar mass can be written in the form of a ratio of molecular mass.
     i = Normal molecular mass / Observed molecular mass
     i = m/mo
During dissociation, (i > 1)
During association, (i < 1)

When i = 1, the solution is an ideal solution that means solute neither undergoes dissociation nor association.

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