Test: Association & Dissociation - JEE MCQ

In benzene, benzoic acid exist as dimer. So the molecular weight of benzoic acid gets doubled.

(C₆​H₅​COOH)_2​=2×122=244 units .

The correct answer is option A
In chemistry, when the molar masses are calculated and if they are higher or lower than the expected value are known as abnormal molar masses. These are calculated using the colligative properties. Colligative properties include; elevation of boiling point, lowering of vapor pressure, freezing point depression, and ease of osmotic pressure. The name in itself has abnormal in it which suggests the abnormality of how the molar masses are being calculated, using the Van’t Hoff factor.

The correct answer is Option B.

The osmotic pressure of the NaCl solution is more due to the Van't Hoff factor of NaCl.
Van't Hoff factor of NaCl is 2.
The Van't Hoff factor of acetic acid is between 1 and 2.
Hence P₁7P₂

Barium Chloride on dissociation gives 2 moles of Chloride ions and one mole of Barium ions so the total number of moles of ions in solution is 2+1=3.0, Higher is the van't Hoff factor greater will be the lowering of vapour pressure.

The correct answer is option D

Increase in the temperature of solution of a weak electrolyte will result in an increase in degree of dissociation causing increase in 
van’t Hoff factor.
 

The correct answer is option C
Since glucose is a nonelectrolyte the van’t Hoff factor i = 1
           ΔT_f= iK_fm
              =1.86 x 0.1
        =0.186
0^oC – T_f =0.186
          T_f= - 0.186^oC

The correct answer is option A
The Van't Hoff Factor is denoted by the letter 'i'. Where abnormal molar mass is determined experimentally and colligative properties are obtained by keeping in mind that solute (non-volatile) is neither associated or dissociated.
The Van’t Hoff Factor is denoted by the letter ‘i’.
Van’t Hoff defined this factor as follows:


Where abnormal molar mass is determined experimentally and colligative properties are obtained by keeping in mind that solute (non-volatile) is neither associated or dissociated.
In the case of dissociation i < 1.
And in the case of association i > .
Thus, equations for colligative properties can be modified as follows after inclusion of Van’t Hoff factors.
Relative lowering of vapour pressure of solvent
(p⁰₁ - p₁)/p⁰₁  = i.(n₂/n₁)
Elevation of boiling point,

Depression of Freezing point,

Osmotic pressure of solutions,

 

The correct answer is Option A.
The Van't Hoff factor of 1:1 electrolyte is 2 since it dissociates into two ions. van’t Hoff factor of a non electrolyte is 1 since it does not dissociate into ions. Hence ratio of osmotic pressure will be 2:1