Chemistry Questions and Answers – Ideal and Non-Ideal Solutions

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This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Ideal and Non-Ideal Solutions”.

1. Which of the following statements regarding Ideal solutions is false?
a) Ideal solutions obey Raoult’s law under all conditions of temperature and concentrations
b) There will be some change in volume on mixing the components, i.e., ΔVmixing ≠ 0
c) There will be no change in enthalpy when the two components are mixed, i.e., ΔHmixing = 0
d) There will be no change in volume on mixing the components, i.e., ΔVmixing = 0
View Answer

Answer: b
Explanation: An ideal solution is the solution in which each component obeys Raoult’s law under all conditions of temperature and concentrations. An ideal solution will satisfy the following conditions:
I. There will be no change in volume on mixing the components, i.e., ΔVmixing = 0.
II. There will be no change in enthalpy (i.e., no heat is evolved or absorbed) when the two components are mixed, i.e., ΔHmixing = 0.

2. Which of the following is not an example of an Ideal solution?
a) Benzene + Toluene
b) n-Hexane + n-Heptane
c) Ethyl alcohol + Water
d) Ethyl bromide + Ethyl chloride
View Answer

Answer: c
Explanation: An ideal solution may be defined as the solution in which no volume change and no enthalpy change take place on mixing the solute and the solvent in any proportion. Ethyl alcohol + Water is a Non-Ideal solution.

3. A solution which does not obey Raoult’s law is called a non-ideal solution.
a) True
b) False
View Answer

Answer: a
Explanation: A non-ideal solution is the solution in which solute and solvent molecules interact with one another with a different force than the forces of interaction between the molecules of the pure components. Non-Ideal solutions do not obey Raoult’s law.
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4. Which of the following is false regarding Non-Ideal solutions?
a) They do not obey Raoult’s law
b) ΔVmixing ≠ 0
c) ΔHmixing = 0
d) They form azeotropes
View Answer

Answer: c
Explanation: Non-Ideal solutions do not obey Raoult’s law. For Non-Ideal solutions, ΔVmixing ≠ 0, ΔHmixing ≠ 0. Non-ideal solutions form azeotropes or constant boiling mixtures, i.e., they have the same concentration in the vapour phase and the liquid phase.

5. Which of the following is an example of a non-ideal solution showing positive deviation?
a) Acetone + Carbon disulphide
b) Chlorobenzene + Bromobenzene
c) Chloroform + Benzene
d) Acetone + Aniline
View Answer

Answer: a
Explanation: Chlorobenzene + Bromobenzene is an example of an ideal solution. Chloroform + Benzene and Acetone + Aniline are examples of non-ideal solutions but they show negative deviations. Acetone + Carbon disulphide is an example of a non-ideal solution showing positive deviation.
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6. Ideal solutions do not form azeotropes.
a) True
b) False
View Answer

Answer: a
Explanation: An azeotrope or a constant boiling mixture is a mixture that has the same concentration in the vapour phase and the liquid phase. In azeotropes, the component ratio of unvaporized solution is equal to that of the vaporized solution when boiling. Hence, Ideal solutions don’t form azeotropes.

7. Which of the following is not an example of a non-ideal solution showing negative deviation?
a) HNO3 + Water
b) HCl + Water
c) Acetic acid + Pyridine
d) Carbon tetrachloride + Toluene
View Answer

Answer: d
Explanation: HNO3 + Water, HCl + Water and Acetic acid + Pyridine are non-ideal solutions showing negative deviations. Carbon tetrachloride + Toluene is an example of non-ideal solution showing positive deviation.
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8. Which of the following is true regarding non-ideal solutions with negative deviation?
a) The interactions between the components are lesser than in the pure components
b) ΔVmixing = +ve
c) ΔHmixing = +ve
d) They form maximum boiling azeotropes
View Answer

Answer: d
Explanation: The interactions between the components of a non-ideal solution showing negative deviation are greater than the pure components. The change in volume and enthalpy after mixing is negative, i.e., ΔVmixing = -ve, ΔHmixing = -ve.

9. Which of the following cannot form an azeotrope?
a) H2O + C2H5OH
b) CHCl3 + C2H5OH
c) HCl + H2O
d) Benzene + Toluene
View Answer

Answer: d
Explanation: H2O + C2H5OH forms an azeotrope with a boiling point of 351.15 K. CHCl3 + C2H5 OH forms an azeotrope with a boiling point of 332.3 K. HCl + H2O forms an azeotrope with a boiling point of 383 K. Benzene + Toluene is an ideal solution and hence does not form an azeotrope.
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10. Which of the following is true regarding azeotropes?
a) An azeotrope does not exhibit the same concentration in the vapour phase and the liquid phase
b) Azeotropic mixtures cannot be separated into their constituents by fractional distillation
c) In case of minimum boiling azeotropes, the boiling point of the azeotrope is higher than the boiling point of either of the pure components
d) In case of maximum boiling azeotropes, the boiling point of the azeotrope is lesser than the boiling point of either of the pure components
View Answer

Answer: b
Explanation: Azeotropes have the same concentration in the vapour phase and the liquid phase. In case of minimum boiling azeotropes, the boiling point of the azeotrope is lesser than the boiling point of either of the pure components. In case of maximum boiling azeotropes, the boiling point of the azeotrope is higher than the boiling point of either of the pure components.

11. If liquids A and B form an ideal solution, then what is the Gibbs free energy of mixing?
a) > 0
b) < 0
c) = 0
d) Not Defined
View Answer

Answer: b
Explanation: The Gibbs free energy of a system at any moment in time is defined as the enthalpy of the system minus the product of the temperature times the entropy of the system. For ideal solutions, the value of the Gibbs Free energy is always negative as mixing of ideal solutions is a spontaneous process.

12. 5 moles of liquid X and 10 moles of liquid Y make a solution having a total vapour pressure 70 torr. The vapour pressures of pure X and pure Y are 64 torr and 76 torr respectively. Which of the following is true regarding the described solution?
a) The solution shows positive deviation
b) The solution shows negative deviation
c) The solution is ideal
d) The solution has volume greater than the sum of individual volumes
View Answer

Answer: b
Explanation: Given,
Observed pressure = 76 torr
According to Raoult’s law,
pA = xA x pA0 = 5/15 x 64 = 21.33 torr
pB = xB x pB0 = 10/15 x 76 = 50.67 torr
Therefore, pressure expected by Raoult’s law = 21.33 + 50.67 = 72 torr.
Thus, observed pressure (70 torr) is less than the expected value. Hence, the solution shows negative deviation.

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