Question

Benzoic acid undergoes dimerisation in benzene. x gram of benzoic acid dissolved in 30 gram of benzene decreases freezing point by 2 Kelvin if Association is 80% and KF equal 5 Kelvin kg per mole molar mass equal 122 gram per mole what is the value of x

Answer 1

Answer:

Mole Concept -

One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012 kg) of the 12C isotope.

- wherein

one mole = 6.0221367 X 1023

Molar Mass -

The mass of one mole of a substance in grams is called its molar mass.

- wherein

Molar mass of water = 18 g mol-1

As e have learned:

The reaction is :

Answer 2

The amount of benzoic acid required i to be dissolved in 30 g of benzene to cause a depression in the freezing point by 2K is equal to 2.44 g.

• The molality of the solution (m) containing x grams of benzoic acid is equal to x×1000/(30×122) = 100x/366 m
• The degree of association (a) is equal to 0.8 so, the Von't Hoff factor (i) is equal to (1-0.5a) = 0.6
• Kf is given to be equal to 5 kg.K/mole
• The formula for the depression in freezing point is : ΔTf = i×m×Kf
• So, 2 = 0.6×(100x/366)×5 ⇒ x = 2×366/(0.6×100×50 ⇒ x = 2.44 g.