Class 12 Chemistry

Chapter 2 - Solutions

(Magical Series) Very Important Questions Set 8

     These Questions were not in 2020-21 Syllabus

Q.1.     Define the van't Hoff factor.

Q.2.     Define the Abnormal molar mass.

Q.3.     What types of values can it have if in forming the solution the solute molecules undergo

(i) dissociation

(ii) association?

Q.4.     Assuming complete dissociation, calculate the expected freezing point of a solution prepared by dissolving 6.00 g of Glauber's salt, Na₂SO₄.10H₂O in 0.100 kg of water. (K_f or water = 1.86 K kg mol^–1, atomic masses: Na = 23, S = 32, O = 16, H = 1).

[Ans: 271.96 K]

Q.5.     A 1.00 molal aqueous solution of trichloroacetic acid (CCl₃COOH) is heated to its boiling point. The solution has the boiling point of 100.18 °C. Determine the van't Hoff factor for trichloroacetic acid. (K_b for water = 0.512 K kg mol^–1).

[Ans: 0.35]

Q.6.     Calculate the freezing point of solution when 1.9 g of MgCl₂ (M = 95 g mol^–1) was dissolved in 50 g of water, assuming MgCl₂ undergoes complete ionization. (K_f for water = 1.86 K kg mol^–1)

[Ans: 270.77 K]

Q.7.     When 2.56 g of sulphur was dissolved in 100 g of CS₂, the freezing point lowered by 0.383 K. Calculate the formula of sulphur (S_x). (K_f the CS₂ = 3.83 K kg mol^–1, atomic mass of sulphur = 32 g mol^–1).

[Ans: S₈]

Q.8.     Calculate the freezing point of an aqueous solution containing 10.50 g of MgBr₂ in 200 g of water. (Molar mass of MgBr₂ = 184 g mol^–1) (K_f for water = 1.86 K kg mol^–1)

[Ans: 271.408 K]

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