CBSE Class 12 Chemistry Solutions Questions

Question. The boiling point of 0.2 mol kg–1 solution of X in water is greater than equimolal solution of Y in water. Which one of the following statements is true in this case?
(a) Molecular mass of X is less than the molecular mass of Y.
(b) Y is undergoing dissociation in water while X undergoes no change.
(c) X is undergoing dissociation in water.
(d) Molecular mass of X is greater than the molecular mass of Y. 

Answer : C

Question. Of the following 0.10 m aqueous solutions, which one will exhibit the largest freezing point depression?
(a) KCl
(b) C₆H₁₂O₆
(c) Al₂(SO₄)₃
(d) K₂SO₄ 

Answer : C

Question. The freezing point of equimolal aqueous solution will be highest for 
(a) C₆H₅NH₃+Cl^–
(b) Ca(NO₃)₂
(c) La(NO₃)₂
(d) C₆H₁₂O₆

Answer : D

Question. Which of the following 0.10 m aqueous solutions will have the lowest freezing point ? 
(a) Al₂(SO₄)₃
(b) C₆H₁₂O₆
(c) KCl
(d) C₁₂H₂₂O₁₁

Answer : A

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

Answer : C

Question. The freezing point depression constant for water is –1.86 °C m^–1. If 5.00 g Na₂SO₄ is dissolved in 45.0 g H₂O, the freezing point is changed by –3.82 °C. Calculate the van’t Hoff factor for Na₂SO₄.
(a) 2.05
(b) 2.63
(c) 3.11
(d) 0.381

Answer : B

Question. A 0.1 molal aqueous solution of a weak acid is 30% ionized. If Kf for water is 1.86°C/m, the freezing point of the solution will be
(a) – 0.18 °C
(b) – 0.54 °C
(c) – 0.36 °C
(d) – 0.24 °C
Answer : D

Question. An aqueous solution is 1.00 molal in KI. Which change will cause the vapour pressure of the solution to increase?
(a) Addition of NaCl
(b) Addition of Na₂SO₄
(c) Addition of 1.00 molal KI
(d) Addition of water 

Answer : D

Question. The vapour pressure of benzene at a certain temperature is 640 mm of Hg. A non-volatile and non-electrolyte solid, weighing 2.175 g is added to 39.08 of benzene. The vapour pressure of the solution is 600 mm of Hg. What is the molecular weight of solid substance?
(a) 69.5
(b) 59.6
(c) 49.50
(d) 79.8 

Answer : A

Question. If 0.15 g of a solute, dissolved in 15 g of solvent, is boiled at a temperature higher by 0.216°C, than that of the pure solvent. The molecular weight of the substance (Molal elevation constant for the solvent is 2.16°C) is
(a) 10.1
(b) 100
(c) 1.01
(d) 1000 

Answer : B

Question. A 5% solution of cane sugar (mol. wt. = 342) is isotonic with 1% solution of a substance X. The molecular weight of X is
(a) 68.4
(b) 171.2
(c) 34.2
(d) 136.8 

Answer : A

Question. The vapour pressure of benzene at 30°C is 121.8 mm. By adding 15 g of non-volatile solute in 250 g of benzene, its vapour pressure is decreased to 120.2 mm. The molecular weight of solute is :
(a) 156.6 g
(b) 267.4 g
(c) 356.3 g
(d) 467.4 g

Answer : C

Question. Pure benzene freezes at 5.45°C. A 0.374 m solution of tetrachloroethane in benzene freezes at 3.55°C. The Kf for benzene is: 
(a) 0.508
(b) 5.08
(c) 50.8
(d) 508

Answer : B

Question. 0.450 g of urea (mol.wt.60) in 22.5 g of water show 0.170°C of elevation in boiling point. The molal elevation constant of water is: 
(a) 0.051°C
(b) 0.51°C
(c) 5.1°C
(d) 0.83°C

Answer : B

Question. On mixing 3 g of non - volatile solute in 200 mL of water, its boiling point (100°C) becomes 100.52°C. If Kb for water is 0.6 K/m then molecular wt. of solute is : 
(a) 10.5 gmol^-1
(b) 12.6 gmol^-1
(c) 15.7 gmol^-1
(d) 17.3 gmol^-1

Answer : D

Question. The colligative property is not represented by :
(a) elevation in boiling point 
(b) osmotic pressure
(c) optical activity
(d) relative lowering of vapour pressure

Answer : C

Question. 20 g of a substance were dissolved in 500 mL of water and the osmotic pressure of the solution was found to be 600 mm of mercury at 15°C. The molecular weight of substance is : 
(a) 998
(b) 1028
(c) 1098
(d) 1198

Answer : D

Question. Which one of the statements given below concerning properties of solutions, describes a colligative effect? 
(a) Boiling point of pure water decreases by the addition of ethanol
(b) Vapour pressure of pure water decreases by the addition of nitric acid
(c) Vapour pressure of pure benzene decreases by the addition of naphthalene
(d) Boiling point of pure benzene increases by the addition of toluene

Answer : C

Question. The average osmotic pressure of human blood is 7.8 bar at 37°C. What is the concentration of an aqueous NaCl solution that could be used in the blood stream? 

(a) 0.16 mol/L
(b) 0.31 mol / L
(c) 0.60 mol / L
(d) 0.45 mol / L

Answer : B

Question. A 5% solution (by mass) of cane sugar in water has freezing point of 271 K and freezing point of pure water is 273.15 K. The freezing point of a 5% solution (by mass) of glucose in water is
(a) 271 K
(b) 273.15K 
(c) 269.07 K
(d) 277.23 K

Answer : C

Question. The vapour pressure of pure benzene at a certain temperature is 0.850 bar. A non-volatile, nonelectrolyte solid weighing 0.5 g is added to 39.0 g of benzene (molar mass 78 g/mol). The vapour pressure of the solution then is 0.845 bar. What is the molecular mass of the solid substance?
(a) 58
(b) 180 
(c) 170
(d) 145.

Answer : C

Question. 1 mol each of the following compounds is dissolved in 1L of solution. Which will have the largest ΔTb value? 
(a) HF
(b) HCl
(c) HBr
(d) HI.

Answer : D

Question. 0.01 M solution of KCl and BaCl2 are prepared in water. The freezing point of KCl is found to be –2°C. What is the freezing point of BaCl2 to be completely ionised ? [2008]
(a) – 3°C
(b) + 3°C
(c) – 2°C
(d) – 4°C

Answer : A

Question. An aqueous solution of hydrochloric acid
(a) Obeys Raoult’s law 
(b) Shows negative deviation from Raoult’s law
(c) Shows positive deviation from Raoult’s law
(d) Obeys Henry’s law at all compositions

Answer : B