Ideal and Non-Ideal Solutions - UNSOLVED PRACTICE SET
Chapter: Solutions | Topic: Ideal and Non Ideal Solutions
IDEAL AND NON-IDEAL SOLUTIONS - UNSOLVED PRACTICE SET
Topic: Ideal and Non Ideal Solutions
Multiple Choice Questions
Q1. An ideal solution is one that:
- Obeys Raoult's law at all concentrations and temperatures
- Shows positive deviation from Raoult's law
- Shows negative deviation from Raoult's law
- Forms an azeotrope
Q2. For an ideal solution, the enthalpy of mixing (ΔHmix) is:
- Positive
- Negative
- Zero
- Very large
Q3. A solution showing positive deviation from Raoult's law has:
- ΔHmix < 0 and ΔVmix < 0
- ΔHmix > 0 and ΔVmix > 0
- ΔHmix = 0 and ΔVmix = 0
- ΔHmix < 0 and ΔVmix > 0
Q4. Which of the following pairs forms an ideal solution?
- Ethanol and water
- Benzene and toluene
- Acetone and chloroform
- Nitric acid and water
Q5. A minimum boiling azeotrope is formed by:
- An ideal solution
- A solution showing positive deviation from Raoult's law
- A solution showing negative deviation from Raoult's law
- A pure liquid
Q6. The azeotropic mixture of ethanol and water boils at:
- 78.2°C (pure ethanol)
- 100°C (pure water)
- 78.2°C (same as pure ethanol)
- 78.15°C, which is lower than both pure components
Short Answer Questions
Q7. Define an ideal solution. What are the characteristics of an ideal solution in terms of ΔHmix, ΔVmix, and intermolecular forces?
Q8. Why does a mixture of ethanol and water show positive deviation from Raoult's law? Explain in terms of intermolecular forces.
Q9. Why does a mixture of acetone and chloroform show negative deviation from Raoult's law? What special interaction occurs?
Q10. What is an azeotrope? Differentiate between minimum boiling and maximum boiling azeotropes with one example of each.
Q11. Your chemistry teacher mixes benzene and toluene in the lab. Predict whether this mixture will behave ideally or non-ideally, and explain why.
Q12. Why is it impossible to separate an azeotropic mixture into pure components by simple distillation?
Long Answer Questions
Q13. Discuss ideal solutions in detail:
(a) Definition and conditions for ideality
(b) Thermodynamic characteristics: ΔHmix = 0, ΔVmix = 0, ΔSmix > 0
(c) Intermolecular forces: A–A ≈ B–B ≈ A–B
(d) Examples: benzene + toluene, n-hexane + n-heptane, chlorobenzene + bromobenzene
(e) Graphical representation of vapour pressure vs. composition
Q14. Explain non-ideal solutions and deviations from Raoult's law:
(a) Positive deviation — causes (weaker A–B interactions), examples (ethanol + water, carbon disulphide + acetone), ΔHmix > 0, ΔVmix > 0
(b) Negative deviation — causes (stronger A–B interactions, H-bonding), examples (acetone + chloroform, HNO₃ + water), ΔHmix < 0, ΔVmix < 0
(c) Azeotropes — definition, types, composition, and boiling points
(d) Graphical representations for all cases
Q15. The concept of ideal and non-ideal solutions is crucial in Indian chemical industry. Discuss:
(a) Why ethanol-water separation is important for India's biofuel program and why azeotropic distillation or molecular sieves are needed
(b) How petroleum refineries use fractional distillation based on Raoult's law principles
(c) The preparation of spirit (alcoholic solutions) and why different concentrations have different applications
(d) Why understanding non-ideality is essential for designing solvents in pharmaceutical manufacturing in India
Numerical / Application-Based Problems
Q16. Benzene (C₆H₆) and toluene (C₇H₈) form an ideal solution. At 30°C, the vapour pressures of pure benzene and toluene are 120 mmHg and 40 mmHg respectively.
(a) Calculate the total vapour pressure of a solution containing 2 moles of benzene and 3 moles of toluene.
(b) Calculate the mole fraction of benzene in the vapour phase.
(c) If the solution is distilled, which component will be enriched in the first fraction collected? Explain.
Q17. A mixture of ethanol and water forms an azeotrope containing 95.6% ethanol by mass, boiling at 78.15°C.
(a) Calculate the mole fraction of ethanol in the azeotrope.
(b) Pure ethanol boils at 78.2°C and pure water at 100°C. Explain why the azeotrope boils at a temperature lower than both components.
(c) If a distillery in Punjab produces 1000 L of 40% ethanol (v/v) fermentation broth, calculate the maximum volume of 95.6% ethanol that can be obtained by simple distillation.
[Given: Densities: ethanol = 0.789 g/mL, water = 1.0 g/mL; Molar masses: ethanol = 46 g/mol, water = 18 g/mol]
Q18. The following data is for a mixture of acetone (A) and chloroform (C) at 35°C:
xA (liquid) = 0.5, pA (observed) = 200 mmHg, p°A = 350 mmHg
xC (liquid) = 0.5, pC (observed) = 160 mmHg, p°C = 300 mmHg
(a) Calculate the expected vapour pressures if the solution were ideal.
(b) Calculate the deviation from Raoult's law for each component.
(c) Determine whether the solution shows positive or negative deviation and explain the molecular reason.
(d) Calculate ΔHmix if the enthalpy of pure components is zero and the mixture releases 500 J per mole of solution.