Question

What is meant by abnormal molar mass of solute? Discuss the factors which bring abnormality in the experimentally determined molecular mass of solutes using colligative property.

Answer 1

Abnormal molar mass: While calculating the molar mass of a substance using colligative properties, we find their molar mass higher or lower than is expected. This observed mass is called abnormal molar mass of that substance

Example:

 2CH3COOH → (CH3COOH)2

When we use colligative properties to calculate the molar mass of a the solute, we assume that:

The solution is dilute thereby obeying Raoult’s law

The solute doesn’t undergo either association or dissociation in solution.

This abnormality in molar mass is observed due to:

Association of solute molecules:

Certain solute molecules associate while in solution. This association decreases the number of molecules in the solution which results in decrease in colligative properties.

Colligative property ∝ 1/ molecular mass of solute

So, in case of association of solute molecules, the calculated values of molecular mass of solute will be more than their normal values

Dissociation of solute molecules:

Some solutes dissociate in solution to give two or more ions, thereby unexpectedly increasing the number of solute particles in solution. So, they exhibit higher values of colligative properties as:

Colligative property ∝ 1/ molecular mass of solute

So, in case of dissociation of solute molecules, the calculated values of molecular mass of solute will be lesser than their normal values.

Answer 2

$\huge\bf{Answer:-}$

Abnormal molar mass:-

The molar mass of a solute in a solution can be determined with the help of molecular numerical properties such as vapor pressure gradient, boiling point gradation, freezing point freezing, and osmotic pressure, but there are some conditions It is as if the solution should not contain computation or ionization of solute,The solvent should be high and the rules of roulette should be followed.

If these conditions are met, then the molar mass of solute can be determined with the help of molecular numerical properties.