CHEMISTRY

Class XII
Time: 3 Hours Maximum Marks: 70

General Instructions:
1. There are 33 questions in this question paper with internal choice.
2. SECTION A consists of 16 multiple-choice questions carrying 1 mark
each.
3. SECTION B consists of 5 questions carrying 2 marks each.
4. SECTION C consists of 7 questions carrying 3 marks each.
5. SECTION D consists of 2 case-based questions carrying 4 marks each.
6. SECTION E consists of 3 long answer questions carrying 5 marks each.
7. All questions are compulsory.
8. Use of log tables and calculators is not allowed.

SECTION A
Select and write the most appropriate answer from the given options for each of
the following questions:
1. Which of the following aqueous solutions will have the highest boiling point?
(a) 0.1 M NaCl
(b) 0.1 M BaCl�
(c) 0.1 M Al�(SO�)�
(d) 0.1 M C�H��O�
2. The molality of a solution containing 18 g of glucose (C�H��O�) in 100 g of
water is:
(a) 0.1 m
(b) 1.0 m
(c) 10 m
(d) 0.01 m
3. Henry’s law is applicable for:
(a) All gases in all solvents
(b) All gases in polar solvents only
(c) Dilute solutions of gases which do not undergo chemical reaction with the
solvent
(d) Concentrated solutions of gases
4. An ideal solution is one which:
(a) Shows positive deviation from Raoult’s law
(b) Shows negative deviation from Raoult’s law

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(c) Obeys Raoult’s law over the entire range of concentration
(d) Shows maximum boiling azeotrope
5. Which of the following solutions will show maximum osmotic pressure?
(a) 1 M NaCl
(b) 1 M BaCl�
(c) 1 M Al(NO�)�
(d) 1 M C��H��O��
6. The relative lowering of vapour pressure is equal to:
(a) Mole fraction of solvent
(b) Mole fraction of solute
(c) Molality of solution
(d) Molarity of solution
7. Which of the following is not a colligative property?
(a) Osmotic pressure
(b) Elevation in boiling point
(c) Viscosity
(d) Depression in freezing point
8. The Van’t Hoff factor for 0.1 M Ba(NO�)� solution is:
(a) 1
(b) 2
(c) 3
(d) 4
9. Which of the following solutions will freeze at the highest temperature?
(a) 0.1 M NaCl
(b) 0.1 M BaCl�
(c) 0.1 M glucose
(d) 0.1 M Al�(SO�)�
10. According to Henry’s law, the partial pressure of a gas in vapour phase (p)
is proportional to the mole fraction of the gas (x) in the solution. The constant
of proportionality is:
(a) Henry’s constant (K_H)
(b) 1/K_H
(c) K_H²
(d) √K_H
11. The ebullioscopic constant of water is 0.52 K kg mol�¹. The boiling point
of 0.1 molal aqueous NaCl solution is approximately:
(a) 100.052°C
(b) 100.104°C
(c) 100.52°C
(d) 101.04°C
12. A solution shows positive deviation from Raoult’s law when:
(a) A-B interactions are stronger than A-A and B-B interactions

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(b) A-B interactions are weaker than A-A and B-B interactions
(c) Volume of mixing is zero
(d) Enthalpy of mixing is zero
For questions 13-16, two statements are given - one labelled Assertion (A) and
the other labelled Reason (R). Select the correct answer using the codes given
below: - (a) Both A and R are true and R is the correct explanation of A - (b)
Both A and R are true but R is not the correct explanation of A - (c) A is true
but R is false - (d) A is false but R is true
13. Assertion (A): 0.1 M NaCl solution has a higher boiling point than 0.1
M glucose solution.
Reason (R): NaCl is an electrolyte while glucose is a non-electrolyte.
14. Assertion (A): Osmotic pressure is a colligative property.
Reason (R): Osmotic pressure depends on the number of solute particles in
solution.
15. Assertion (A): Addition of ethylene glycol to water lowers the freezing
point of water.
Reason (R): Ethylene glycol is a non-volatile solute.
16. Assertion (A): Azeotropic mixtures are formed only by non-ideal solu-
tions.
Reason (R): The composition of vapour phase is different from the composition
of liquid phase in azeotropic mixtures.

SECTION B
All questions are compulsory. In case of internal choice, attempt any one.
17. Define osmotic pressure. Write the mathematical expression for osmotic
pressure and explain each term involved. (2 marks)
18. Calculate the molality of a solution prepared by dissolving 2.5 g of ethanoic
acid (CH�COOH) in 75 g of benzene. (2 marks)
19. State Henry’s law. Give two applications of Henry’s law. (2 marks)
OR
State Raoult’s law for volatile components. What type of deviation from
Raoult’s law is shown by a mixture of ethanol and acetone?
20. What are isotonic solutions? Give one example. (2 marks)
21. A 0.001 molal solution of a complex MA� in water has a freezing point of
-0.0054°C. Calculate the Van’t Hoff factor. (K_f for water = 1.86 K kg mol�¹)
(2 marks)

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SECTION C
All questions are compulsory. In case of internal choice, attempt any one.
22. Explain the following observations:
(a) Ethanol and acetone mixture shows positive deviation from Raoult’s law.
(b) Addition of NaCl to water decreases the freezing point of water.
(c) Osmotic pressure method is preferred for determining molar masses of macro-
molecules. (3 marks)
23. Calculate the mass of urea (NH�CONH�) required to be dissolved in 1000
g of water so that the freezing point is depressed by 3.72°C. (K_f for water =
1.86 K kg mol�¹, Molar mass of urea = 60 g mol�¹) (3 marks)
24. (a) What is meant by abnormal molar mass?
(b) When is the molecular mass higher than expected and when is it lower than
expected? Give one example each. (3 marks)
OR
(a) Define the term ‘molal elevation constant’ or ‘ebullioscopic constant’.

(b) The boiling point of benzene is 353.23 K. When 1.80 g of a non-volatile

solute was dissolved in 90 g of benzene, the boiling point is raised to 354.11
K. Calculate the molar mass of the solute. (K_b for benzene = 2.53 K kg
mol�¹)
25. A solution of glucose (C�H��O�) in water is labelled as 10% by weight. What
would be the molality and mole fraction of glucose in the solution? (3 marks)
26. The vapour pressure of pure acetone (CH�COCH�) at 20°C is 185 torr.
When 1.2 g of a non-volatile substance is dissolved in 100 g of acetone, its
vapour pressure becomes 183 torr. Calculate the molar mass of the substance.
(3 marks)
27. Explain the following:
(a) Out of 1 M glucose and 1 M KCl, which one will have a higher boiling point
and why?
(b) Seawater is desalinated by reverse osmosis.
(c) Ethylene glycol is used as antifreeze in automobile radiators. (3 marks)
28. Henry’s law constant for CO� in water is 1.67 × 10� Pa at 298 K. Calculate
the quantity of CO� in 500 mL of soda water when packed under 2.5 atm CO�
pressure at 298 K. (3 marks)

SECTION D
Both questions are compulsory.

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29. Case Study 1: Read the passage given below and answer the questions
that follow:
Colligative properties are those properties of solutions which depend only on
the number of solute particles and not on the nature of solute particles. The
four important colligative properties are: relative lowering of vapour pressure,
elevation in boiling point, depression in freezing point, and osmotic pressure.
For electrolytes, the Van’t Hoff factor (i) is used to account for the dissociation
of solute particles.
A scientist prepared three solutions: - Solution A: 0.1 M glucose (C�H��O�) -
Solution B: 0.1 M sodium chloride (NaCl)
- Solution C: 0.1 M calcium chloride (CaCl�)
(i) Which solution will have the highest osmotic pressure? (1 mark)
(a) Solution A (b) Solution B (c) Solution C (d) All have equal osmotic pressure
(ii) The Van’t Hoff factor for NaCl in dilute solution is approximately: (1
mark)
(a) 1 (b) 1.8 (c) 2 (d) 3
(iii) Which solution will have the lowest freezing point? (1 mark)
(a) Solution A (b) Solution B (c) Solution C (d) Cannot be determined
(iv) If the freezing point of solution B is -0.372°C, what is the Van’t Hoff factor?
(K_f for water = 1.86 K kg mol�¹) (1 mark)
(a) 1.5 (b) 2.0 (c) 2.5 (d) 3.0
30. Case Study 2: Read the passage given below and answer the questions
that follow:
Raoult’s law states that the partial pressure of each component of an ideal
solution is proportional to its mole fraction in the solution. Real solutions often
deviate from Raoult’s law. When A-B interactions are weaker than A-A and B-
B interactions, the solution shows positive deviation from Raoult’s law. When
A-B interactions are stronger than A-A and B-B interactions, the solution shows
negative deviation.
Examples of positive deviation: ethanol-water, benzene-acetone
Examples of negative deviation: acetone-chloroform, HNO�-water
(i) In positive deviation from Raoult’s law: (1 mark)
(a) P_total < P_ideal (b) P_total > P_ideal (c) P_total = P_ideal (d) Cannot
be predicted
(ii) Ethanol-water mixture shows positive deviation because: (1 mark)
(a) Hydrogen bonding between ethanol and water is stronger
(b) Hydrogen bonding between ethanol and water is weaker than individual
hydrogen bonding
(c) There is no hydrogen bonding
(d) Molecular sizes are different

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(iii) Which of the following will form minimum boiling azeotrope? (1 mark)
(a) Acetone-chloroform (b) Ethanol-water (c) HNO�-water (d) Both (a) and (c)
(iv) For a solution showing negative deviation, the enthalpy of mixing
(ΔH_mix) is: (1 mark)
(a) Positive (b) Negative (c) Zero (d) Cannot be predicted

SECTION E
All questions are compulsory. In case of internal choice, attempt any one.
31. (a) What are colligative properties? Why are they called colligative prop-
erties?
(b) Derive the relationship between elevation in boiling point and molal concen-
tration of solution.
(c) 1.00 g of a non-electrolyte solute dissolved in 50 g of benzene lowered the
freezing point by 0.40 K. Find the molar mass of the solute. (K_f for benzene
= 5.12 K kg mol�¹) (5 marks)
32. (a) State and explain Henry’s law. Write its mathematical expression.
(b) What is the effect of temperature on Henry’s law constant?
(c) At 293 K, Henry’s law constant for oxygen dissolved in water is 4.6 × 10�
atm. Calculate the mass of oxygen dissolved in 1 litre of water under oxygen
pressure of 1 atm at 293 K. (5 marks)
OR
(a) Define osmosis and osmotic pressure.

(b) Derive the relationship: � = iCRT

(c) Calculate the osmotic pressure of 0.05 M urea solution at 300 K. (R =

0.0821 L atm K�¹ mol�¹)
33. (a) What are ideal and non-ideal solutions? Give one example each of
positive and negative deviation from Raoult’s law.
(b) The vapour pressures of pure liquids A and B are 450 mm Hg and 700 mm
Hg respectively at 350 K. Find the composition of the liquid mixture if the total
vapour pressure is 600 mm Hg. Also find the composition in the vapour phase.
(5 marks)

MARKING SCHEME
SECTION A (16 × 1 = 16 marks) 1. (c) 2. (b) 3. (c) 4. (c) 5. (c) 6. (b)
7. (c) 8. (c) 9. (c) 10. (a) 11. (b) 12. (b) 13. (a) 14. (a) 15. (a) 16. (c)

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SECTION D Case Studies: Q29: (i) (c) (ii) (c) (iii) (c) (iv) (b) Q30: (i)
(b) (ii) (b) (iii) (b) (iv) (b)
Note: This question paper is designed according to the latest CBSE Class 12
Chemistry exam pattern 2025-26, focusing specifically on Chapter 1 - Solutions.
It covers all important concepts including types of solutions, concentration terms,
Raoult’s law, Henry’s law, colligative properties, ideal and non-ideal solutions,
and Van’t Hoff factor.