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

Question. If two bottles A and B contain 1 M and 1 m aqueous solution of sulphuric acid respectively,

a) A is more concentrated than B
b) B is more concentrated than A
c) concentration of A is equal to concentration of B
d) it is not possible to compare the concentration

Answer: b

Question. When a binary solution of two volatile liquids is taken in a closed vessel, then
a) Both the components would evaporate and an equilibrium would be established between vapour phase and liquid phase
b) Both the components would evaporate but equilibrium would not be established between vapour phase and liquid phase
c) None of components would evaporate and no equilibrium would be established between vapour phase and
liquid phase
d) None of the above

Answer: a

Question. What is the percentage of solute in the resultant solution, if it is obtained by mixing 300g of 30% and 200g of 20% solution by weight?
a) 50%
b) 26%
c) 62%
d) 32%

Answer: b

Question. The vapour pressure of pure CHCl₃ and CH₂Cl₂ are 200 and 41.5 atm respectively. The weight of CHCl₃ and CH₂ Cl₂ are respectively 11.9 g and 17 g.
The vapour pressure of solution will be
a) 80.5 atm
b) 79.5 atm
c) 94.3 atm
d) 105.5 atm

Answer: c

Question. A 5.2 molal aqueous solution of methyl alcohol, CH₃OH  is supplied. What is the mole fraction of methyl alcohol in the solution?
a) 1.100
b) 0.090
c) 0.086
d) 0.050

Answer: c

Question. The solubility of N₂ in water at 300 K and 500 torr partial pressure is 0.01g L⁻¹ . The solubility in(g L⁻¹ )  at 750 torr partial pressure is
a) 0.02
b) 0.015
c) 0.0075
d) 0.005

Answer: b

Question. At 300 K two pure liquids A and B have 150 mm Hg and 100 mm Hg vapour pressures, respectively. In an equimolar liquid mixture of A and B, the mole fraction of B in the vapour mixture at this temperature is
a) 0.6
b) 0.5
c) 0.8
d) 0.4

Answer: d

Question. Calculate the concentration of nitrogen present in the water. Assuming that, the temperature is 25°C, total pressure is 1 atm and mole fraction of nitrogen is 0.78. [K_H for nitrogen 8.42×10⁻⁷ = M/mm Hg]
a) 4.99 M
b) 4.99×10⁻²M  
c) 4.99×10⁻⁴M
d) None of these

Answer: c

Question. The van’t Hoff factor (i) for a compound which undergoes dissociation in one solvent and association in other solvent is respectively
a) greater than one and greater than one
b) less than one and greater than one
c) less than one and less than one
d) greater than one and less than one

Answer: d

Question. For an ideal solution, the correct option is
a) Δ_mix V ≠ 0 at constant T and p
b) Δ_mix H= 0 at constant T and p
c) Δ_mix G= 0 at constant T and p
d) Δ_mix S= 0 at constant T and p

Answer: b

Question. The solution which show large positive deviation from Raoult’s law form
a) maximum boiling azeotrope at a specific composition.
b) maximum freezing azeotrope at a specific composition.
c) minimum boiling azeotrope at a specific composition.
d) minimum freezing azeotrope at a specific composition.

Answer: c

Question. What is the molarity of K⁺ in aqueous solution that contains 17.4 ppm of K₂ SO₄ (Molar mass =174 g mol⁻¹ ) ?
a) 2×10⁻² M
b) 2×10⁻³ M
c) 4×10⁻⁴M
d) 2×10⁻⁴M

Answer: d

Question. The examples of minimum boiling azeotropes are
a) aniline + acetone
b) acetic acid + pyridine
c) HCl + water
d) cyclohexane + ethanol

Answer: d

Question. Relative lowering of vapour pressure is a colligative property because
a) it depends on the concentration of a non-electrolyte solute in solution and does not depend on the nature of the solute molecules
b) it depends on number of particles of electrolytic solute in solution as well as on the nature of the solute particles
c) it depends on the concentration of a non-electrolyte solute in solution as well as on the nature of the solute molecules
d) it depends on the concentration of an electrolyte or non-electrolyte solute in solution as well as on the nature of solute molecules

Answer: a

Question. The solution that forms maximum boiling azeotrope is
a) carbon disulphide − acetone
b) benzene − toluene
c) acetone − chloroform
d) n-hexane − n-heptane

Answer: c

Question. At room temperature, a dilute solution of urea is prepared by dissolving 0.60 g of urea in 360 g of water. If the vapour pressure of pure water at this temperature is 35 mm Hg, lowering of vapour pressure will be (Molar mass of urea = 60 g mol⁻¹)
a) 0.027 mm Hg
b) 0.031 mm Hg
c) 0.017 mm Hg
d) 0.028 mm Hg

Answer: c

Question. Ethylene glycol is used as an antifreeze in a cold climate. Mass of ethylene glycol which should be added to 4 kg of water to prevent it from freezing at −6°Cwill be (K_f for water =1.86K kg mol⁻¹ and molar mass of ethylene glycol = 62 g mol⁻¹ )
a) 804.32 g
b) 204.30 g
c) 400.00 g
d) 304.60 g

Answer: a

Question. Osmotic pressure method is used to determine molar mass of protein, macromolecules like polymers, biomolecules etc., because
a) osmotic pressure is measured at room temperature
b) osmotic pressure depends upon molality
c) these are not stable at higher temperature and have poor solubility
d) All of the above

Answer: c

Question. If boiling point of water is 100°C. How much gram of NaCl is added in 500 g of water to increase its boiling point by approx 1°C? [(K_b)H₂O  = 0.52 K kg mol⁻¹ ]
a) 2.812 g
b) 28.12 g
c) 14.06 g
d) 7.03 g

Answer: b

Question. Vapour pressure of pure benzene is 119 torr and that of toluene is 37.0 torr at the same temperature. Mole fraction of toluene in vapour phase which is in equilibrium with solution of benzene and toluene having a mole fraction of toluene 0.50, will be
a) 0.137
b) 0.237
c) 0.435
d) 0.205

Answer: b

Question. The osmotic pressure of a dilute solution of an ionic compound XY in water is four times that of a solution of 0.01 M BaCl₂ in water. Assuming complete dissociation of the given ionic compounds in water, the concentration of XY (in mol L⁻¹ ) in solution is
a) 4×10⁻²
b) 16×10⁻⁴
c) 4×10⁻⁴
d) 6×10⁻²

Answer: d

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