CBSE Class 12 Chemistry Solutions MCQs Set N

Question: Raoult’s law becomes a special case of Henry’s law when
a) KH > p₁°
b) KH = p₁°
c) KH < p₁°
d) KH ≥ p₁°
Answer: b

Question: Which of the following condition is not satisfied by an ideal solution?
a) ΔHmixing = 0
b) Raoult’s law is obeyed
c) ΔVmixing = 0
d) Formation of an azeotropic mixture
Answer: d

Question: Iodine and sulphur dissolve in
a) Water
b) Benzene
c) Carbon disulphide
d) Ethanol
Answer: c

Question: The molal elevation constant depends upon
a) Nature of solute
b) Vapour pressure of the solution
c) Nature of the solvent
d) Enthalpy change
Answer: c

Question: According to Raoult’s law, relative lowering of vapour pressure for a solution is equal to
a) Mole fraction of solvent
b) Mole fraction of solute
c) Moles of solute
d) Moles of solvent
Answer: b

Question: People living at high altitudes often feel weak and unable to think clearly. The reason is
a) Partial pressure of oxygen is equal to ground level
b) Partial pressure of oxygen is more than ground level
c) Partial pressure of oxygen is less than ground level
d) None of these
Answer: c

Question: The boiling point of an azeotropic mixture of water and ethanol is less than that of water and ethanol. The mixture shows
a) No deviation from Raoult’s law
b) Negative deviation from Raoult’s law
c) The solution is unsaturated
d) Positive deviation from Raoult’s law
Answer: d

Question: Mole fraction of glycerine C₃H₅(OH)₃ in solution containing 36 g of water and 46 g of glycerine is
a) 0.46
b) 0.20
c) 0.36
d) 0.40
Answer: b

Question: Which has the lowest boiling point at 1 atm pressure?
a) 0.1 M KCl
b) 0.1 M CaCl₂
c) 0.1 M AlCl₃
d) 0.1 M Urea
Answer: d

Question: “The importance of many pure substances in life depends on their composition.” Which of the following justify this statement?
a) 1 ppm of fluoride ions in water prevents tooth decay
b) 1.5 ppm of fluoride ions causes tooth decay
c) Concentration above 1.5 ppm can be poisonous
d) All of the above
Answer: d

Question: 1 M, 2.5 litre NaOH solution is mixed with another 0.5 M, 3 litre NaOH solution. The molarity of the resultant solution is
a) 0.50 M
b) 1.0 M
c) 0.73 M
d) 0.80 M
Answer: c

Question: ____ a contemporary of Henry concluded independently that solubility of a gas in a liquid solution is a function of ____ of the gas.
a) Mosley, temperature
b) Dalton, temperature
c) Mosley, partial pressure
d) Dalton, partial pressure
Answer: d

Question: Osmotic pressure of a solution is 0.0821 atm at 300 K. The concentration in mol L⁻¹ is
a) 0.33
b) 3
c) 0.666
d) 0.3 × 10⁻²
Answer: d

Question: Out of molality (m), molarity (M), formality (F) and mole fraction (x), those which are independent of temperature are
a) M, m
b) F, x
c) m, x
d) M, x
Answer: c

Assertion-Reason Type Questions

DIRECTION: Mark the option which is most suitable:
(a) Assertion and Reason both are correct statements and Reason is correct explanation for Assertion.
(b) Assertion and Reason both are correct statements but Reason is not correct explanation for Assertion.
(c) Assertion is correct statement but Reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question: Assertion: 1 M glucose will have a higher boiling point than 2 M glucose.
Reason: Elevation in boiling point is a colligative property which depends upon the number of particles of solute in the solution.
Answer: d

Question: Assertion: An isotonic solution exerts same osmotic pressure under similar conditions.
Reason: Solute-solvent dipolar interactions exist in the pair of isotonic solution.
Answer: b

Question: Assertion: An aqueous solution of NaCl freezes below 273 K.
Reason: Vapour pressure of the solution is less than that of the pure solvent.
Answer: a

Question: Assertion: Barium Chloride is more effective in causing coagulation than Potassium Chloride.
Reason: Ba2+ has greater valency of 2 than one valency of K+.
Answer: a

Question: Assertion: On adding a non-volatile solute to a solvent, the vapour pressure of the solution get lowered.
Reason: A solution is said to be ideal if it strictly obeys Raoult’s law at all concentrations and temperatures.
Answer: b

Question: Assertion: The Semipermeable membrane made of copper (II) ferrocyanide Cu2[Fe(CN)6] is not used for studying osmosis in a non-aqueous solution.
Reason: Copper (II) ferrocyanide is soluble in non-aqueous medium and insoluble in water.
Answer: a

Question: Assertion: The boiling point of an azeotropic mixture of water and ethanol is less than that of water and ethanol.
Reason: Azeotropic mixture of water and ethanol show positive deviation from Raoult’s law.
Answer: a

Question: Assertion: Molality is independent of temperature whereas molarity in a function of temperature.
Reason: Volume depends on temperature and mass does not depend on temperature.
Answer: a

Question: Assertion: Soft drink and soda water bottles are sealed under high pressure.
Reason: The dissolution of gas in liquid is an endothermic process.
Answer: c

Question: Assertion: The aquatic species feel more comfortable in winter due to single space low temperature.
Reason: Solubility of gases increases with increase of temperature.
Answer: c

Case Based Questions

The concentration of a solute is very important in studying chemical reactions because it determines how often molecules collide in solution and thus indirectly determine the rate of reactions and the conditions at equilibrium.

There are several ways to express the amount of solute present in a solution. The concentration of a solution is a measure of the amount of solute that has been dissolved in a given amount of solvent or solution. Concentration can be expressed in terms of molarity, molality, parts per million, mass percentage, volume percentage etc.

Answer the following MCQs by choosing the most appropriate option:

Question: Which of the following is true for an aqueous solution of the solute in terms of concentration?
a) 1 M = 1 m
b) 1 M > 1 m
c) 1 M < 1 m
d) Cannot be predicted
Answer: b

Question: The molarity (in mol L⁻¹) of the given solution will be
a) 1.56
b) 1.89
c) 0.263
d) 1.44
Answer: d

Question: Which of the following is temperature dependent?
a) Molarity
b) Molality
c) Mole fraction
d) Mass percentage
Answer: a

Question: A solution is prepared using aqueous KI which is found to be 20% w/w. Density of KI solution is 1.202 g/mL. The molality of the given solution and mole fraction of solute are respectively
a) 1.95 m, 0.120
b) 1.5 m, 0.0263
c) 2.5 m, 0.0569
d) 3.0 m, 0.0352
Answer: b

The Properties of the solutions which depend only on the number of solute Particles but not on the nature of the solute are called colligative properties. Relative lowering in vapour pressure is also an example of colligative properties. For an experiment, sugar solution is prepared for which lowering in vapour pressure was found to be 0.061 mm of Hg. (Vabour pressure of water at 20ºC is 17.5 mm of Hg).
Answer the following MCQs by choosing the most appropriate options:

Question: The vapour pressure (mm of Hg) of solution will be
a) 17.5
b) 0.61
c) 17.439
d) 0.00348
Answer: c

Question: The vapour pressure (mm of Hg) of water at 293 K when 25 g of glucose is dissolved in 450 g of water is
a) 17.2
b) 17.4
c) 17.120
d) 17.02
Answer: b

Question: Mole fraction of sugar in the solution is
a) 0.00348
b) 0.9965
c) 0.061
d) 1.75
Answer: a

Question: Relative lowering of vapour pressure for the given solution is
a) 0.00348
b) 0.061
c) 0.122
d) 1.75
Answer: a

Question: If weight of sugar taken is 5 g in 108 g of water, then molar mass of sugar will be
a) 358
b) 120
c) 240
d) 400
Answer: c

At 298 K, the vapour pressure of pure benzene, C₆H₆ is 0.256 bar and the vapour pressure of pure toluene C₆H₅CH₃ is 0.0925 bar. Two mixtures were prepared as follows:
(I) 7.8 g of C₆H₆ + 9.2 g of toluene
(II) 3.9 g of C₆H₆ + 13.8 g of toluene
Answer the following MCQs by choosing the most appropriate option:

Question: Solution I is an example of a/an
a) Ideal solution
b) Non-ideal solution with positive deviation
c) Non-ideal solution with negative deviation
d) Cannot be predicted
Answer: a

Question: Which of the given solutions have higher vapour pressure?
a) I
b) II
c) Both have equal vapour pressure
d) Cannot be predicted
Answer: a

Question: The total vapour pressure (bar) of Solution I is
a) 0.128
b) 0.174
c) 0.198
d) 0.258
Answer: b

Question: Mole fraction of benzene in vapour phase in Solution I is
a) 0.128
b) 0.174
c) 0.734
d) 0.266
Answer: c

Question: Which of the following statements is/are correct?
I. Mole fraction of toluene in vapour phase is more in solution I.
II. Mole fraction of toluene in vapour phase is less in solution I.
III. Mole fraction of benzene in vapour phase is less in Solution I.
a) Only II
b) Only I
c) I and III
d) II and III
Answer: a

Boiling point or freezing point of liquid solution would be affected by the dissolved solids in the liquid phase. A soluble solid in solution has the effect of raising its boiling point and depressing its freezing point. The addition of non-volatile substances to a solvent decreases the vapor pressure and the added solute particles affect the formation of pure solvent crystals. According to many researches the decrease in freezing point directly correlated to the concentration of solutes dissolved in the solvent. This phenomenon is expressed as freezing point depression and it is useful for several applications such as freeze concentration of liquid food and to find the molar mass of an unknown solute in the solution. Freeze concentration is a high quality liquid food concentration method where water is removed by forming ice crystals. This is done by cooling the liquid food below the freezing point of the solution. The freezing point depression is referred as a colligative property and it is proportional to the molar concentration of the solution (m), along with vapor pressure lowering, boiling point elevation, and osmotic pressure. These are physical characteristics of solutions that depend only on the identity of the solvent and the concentration of the solute. The characters are not depending on the solute’s identity.
(Source: Jayawardena, J. A. E. C., Vanniarachchi, M. P. G.,& Wansapala, M. A. J. (2017). Freezing point depression of different Sucrose solutions and coconut water.)

Answer the following MCQs by choosing the most appropriate options:

Question: Identify which of the following is a colligative property?
a) Freezing point
b) Boiling point
c) Osmotic pressure
d) All of the above
Answer: c

Question: Colligative properties are
a) Dependent only on the concentration of the solute and independent of the solvent’s and solute’s identity
b) Dependent only on the identity of the solute and the concentration of the solute and independent of the solvent’s identity
c) Dependent on the identity of the solvent and solute and thus on the concentration of the solute
d) Dependent only on the identity of the solvent and the concentration of the solute and independent of the solute’s identity
Answer: d

Question: Assume three samples of juices A, B and C have glucose as the only sugar present in them. The concentration of samples A, B and C are 0.1 M, 0.5 M and 0.2 M respectively. Freezing point will be highest for the fruit juice
a) A
b) B
c) C
d) All have same freezing point
Answer: a

Question: When a non-volatile solid is added to pure water it will
a) Boil above 100ºC and freeze above 0ºC
b) Boil below 100ºC and freeze above 0ºC
c) Boil above 100ºC and freeze below 0ºC
d) Boil below 100ºC and freeze below 0ºC
Answer: c

The solubility of gases increases with increase of pressure. William Henry made a systematic investigation of the solubility of a gas in a liquid. According to Henry’s law “the mass of a gas dissolved per unit volume of the solvent at constant temperature is directly proportional to the pressure of the gas in equilibrium with the solution”.
Dalton during the same period also concluded independently that the solubility of a gas in a liquid solution depends upon the partial pressure of the gas. If we use the mole fraction of gas in the solution as a measure of its solubility, then Henry’s law can be modified as “the partial pressure of the gas in the vapour phase is directly proportional to the mole fraction of the gas in the solution”.
Answer the following MCQs by choosing the most appropriate options:

Question: The partial pressure of ethane over a saturated solution containing 6.56 × 10⁻² g of ethane is 1 bar. If the solution contains 5.00 × 10⁻² g of ethane, then the partial pressure (in bar) of the gas will be
a) 0.762
b) 1.312
c) 3.81
d) 5.0
Answer: a

Question: Which of the following statements is correct?
a) KH increases with increase of temperature
b) KH decreases with increase of temperature
c) KH remains constant with increase of temperature
d) KH first increases then decreases with increase of temperature
Answer: a

Question: KH (K bar) values for Ar(g), CO₂(g), HCHO(g) and CH₄(g) are 40.39, 1.67, 1.83 × 10⁻⁵ and 0.413 respectively. Arrange these gases in the order of their increasing solubility
a) HCHO < CH₄ < CO₂ < Ar
b) HCHO < CO₂ < CH₄ < Ar
c) Ar < CO₂ < CH₄ < HCHO
d) Ar < CH₄ < CO₂ < HCHO
Answer: c

Question: Henry’s law constant for the solubility of methane in benzene at 298 K is 4.27 × 10⁵ mm Hg. The solubility of methane in benzene at 298 K under 760 mm Hg is
a) 4.27 × 10⁻⁵
b) 1.78 × 10⁻³
c) 4.27 × 10⁻³
d) 1.78 × 10⁻⁵
Answer: b

Question: When a gas is bubbled through water at 298 K, a very dilute solution of the gas is obtained. Henry’s law constant for the gas at 298 K is 150 K bar. If the gas exerts a partial pressure of 2 bar, the number of millimoles of the gas dissolved in 1 L of water is
a) 0.55
b) 0.87
c) 0.37
d) 0.66
Answer: c