CBSE Class 12 Chemistry Solutions Assignment

Question. A solution has a 1 : 4 mole ratio of pentane to hexane.
The vapour pressures of the pure hydrocarbons at 20 °C are 440 mm Hg for pentane and 120 mm Hg for hexane. The mole fraction of pentane in the vapour phase would be
(a) 0.200
(b) 0.549
(c) 0.786
(d) 0.478 

Answer : D

Question. A solution of sucrose (molar mass = 342 g mol^–1) has been prepared by dissolving 68.5 g of sucrose in 1000 g of water. The freezing point of the solution obtained will be (Kf for water = 1.86 K kg mol^–1)
(a) – 0.372 °C
(b) – 0.520 °C
(c) + 0.372 °C
(d) – 0.570 °C 

Answer : A

Question. A solution of urea (mol. mass 56 g mol^–1) boils at 100.18°C at the atmospheric pressure. If Kf and Kb for water are 1.86 and 0.512 K kg mol^–1 respectively, the above solution will freeze at
(a) 0.654°C
(b) – 0.654°C
(c) 6.54°C
(d) – 6.54°C

Answer : B

Question. Pure water can be obtained from sea water by
(a) centrifugation
(b) plasmolysis
(c) reverse osmosis
(d) sedimentation.

Answer : C

Question. From the colligative properties of solution, which one is the best method for the determination of molecular weight of proteins and polymers?
(a) Osmotic pressure
(b) Lowering in vapour pressure
(c) Lowering in freezing point
(d) Elevation in boiling point 

Answer : A

Question. The relationship between osmotic pressure at 273 K when 10 g glucose (p1), 10 g urea (p2), and 10 g sucrose (p3) are dissolved in 250 mL of water is
(a) p2 > p1 > p3
(b) p2 > p3 > p1
(c) p1 > p2 > p3
(d) p3 > p1 > p2 

Answer : A

Question. According to Raoult’s law, the relative lowering of vapour pressure for a solution is equal to
(a) mole fraction of solute
(b) mole fraction of solvent
(c) moles of solute
(d) moles of solvent.

Answer : A

Question. If 0.1 M solution of glucose and 0.1 M solution of urea are placed on two sides of the semipermeable membrane to equal heights, then it will be correct to say that
(a) there will be no net movement across the membrane
(b) glucose will flow towards glucose solution
(c) urea will flow towards glucose solution
(d) water will flow from urea solution to glucose.

Answer : A

Question. A 0.0020 m aqueous solution of an ionic compound [Co(NH₃)₅(NO₂)]Cl freezes at –0.00732 °C. Number of moles of ions which 1 mol of ionic compound produces on being dissolved in water will be (Kf = –1.86 °C/m)
(a) 3
(b) 4
(c) 1
(d) 2

Answer : D

Question. 0.5 molal aqueous solution of a weak acid (HX) is 20% ionised. If Kf for water is 1.86 K kg mol^–1, the lowering in freezing point of the solution is
(a) 0.56 K
(b) 1.12 K
(c) –0.56 K
(d) –1.12 K

Answer : B

Question. Which one is a colligative property?
(a) Boiling point
(b) Vapour pressure
(c) Osmotic pressure
(d) Freezing point 

Answer : C

Question. Blood cells retain their normal shape in solution which are
(a) hypotonic to blood
(b) isotonic to blood
(c) hypertonic to blood
(d) equinormal to blood.

Answer : B

Question. The relative lowering of the vapour pressure is equal to the ratio between the number of
(a) solute molecules to the solvent molecules
(b) solute molecules to the total molecules in the solution
(c) solvent molecules to the total molecules in the solution
(d) solvent molecules to the total number of ions of the solute.

Answer : B

Question. The van’t Hoff factor (i) for a dilute aqueous solution of the strong electrolyte barium hydroxide is
(a) 0
(b) 1
(c) 2
(d) 3

Answer : D

Question. Which of the following 0.10 m aqueous solution will have the lowest freezing point?
(a) KI
(b) C₁₂H₂₂O₁₁
(c) Al2(SO₄)₃
(d) C5H₁₀O₅ 

Answer : C