Concentration expresses how much solute is present in a solution, and NCERT uses several interchangeable scales for it. Mass percentage () is mass of solute per 100 g of solution; mole fraction () is moles of one component over total moles of all components, with all mole fractions in a solution summing to 1; molarity () is moles of solute per litre of solution; and **mo
Solutions
Class 1212 previous-year questions from this chapter every option and the correct answer, free · where the marks are
1. Concentration terms, Henry's and Raoult's laws
Exam focus: A higher Henry's law constant means lower gas solubility, not higher — an inverse relationship (p = KH·x) that's easy to flip under pressure. For non-ideal solutions, positive deviation from Raoult's law (weaker A–B interactions, e.g. ethanol–acetone) gives a minimum-boiling azeotrope, while negative deviation (stronger A–B interactions from H-bonding, e.g. chloroform–acetone) gives a maximum-boiling one — a pairing students often reverse.
Solutions — Full Chapter (Concentration Terms, Henry's and Raoult's Laws)
NCERT Wallah
A full-chapter lecture on Class 12 Solutions. Concentration terms (molarity/molality/mole fraction), Henry's law and Raoult's law are covered in depth, but the video continues into colligative properties and the van't Hoff factor beyond this subtopic.
ChemistryNEET 2025show ▾5 moles of liquid X and 10 moles of liquid Y make a solution having a vapour pressure of 70 torr. The vapour pressures of pure X and Y are 63 torr and 78 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 a volume greater than the sum of the individual volumes.
Solution
Raoult's law predicts torr. The observed 70 torr is lower, so the solution shows negative deviation (stronger A–B interactions).
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Save for spaced revision (free account)ChemistryNEET 2025show ▾Match List I with List II.
List I (Example) List II (Type of solution) A. Humidity I. Solid in solid B. Alloys II. Liquid in gas C. Amalgams III. Solid in gas D. Smoke IV. Liquid in solid
Choose the correct answer from the options given below:
- A.A-II, B-IV, C-I, D-III
- B.A-II, B-I, C-IV, D-III✓
- C.A-III, B-I, C-IV, D-II
- D.A-III, B-II, C-I, D-IV
Solution
Humidity is water vapour (liquid) dispersed in air (gas) — II. Alloys are solid in solid — I. Amalgams are mercury (liquid) in a solid metal — IV. Smoke is solid particles in gas — III. Hence A-II, B-I, C-IV, D-III.
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Save for spaced revision (free account)ChemistryNEET 2024show ▾The Henry's law constant () values of three gases (A, B, C) in water are 145, and 35 kbar, respectively. The solubility of these gases in water follows the order:
- A.B > C > A✓
- B.A > C > B
- C.A > B > C
- D.B > A > C
Solution
Henry's law : a larger means a lower mole fraction dissolved at a given pressure. Solubility therefore increases as falls: B () > C (35) > A (145).
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Save for spaced revision (free account)ChemistryNEET 2022show ▾In a one molal solution that contains 0.5 mole of a solute, there is:
- A.1000 g of solvent
- B.500 mL of solvent
- C.500 g of solvent✓
- D.100 mL of solvent
The worked solution is part of a paid pack.
ChemistryNEET 2021show ▾The correct option for the value of the vapour pressure of a solution at 45 °C with benzene to octane in a molar ratio 3 : 2 is (at 45 °C the vapour pressure of benzene is 280 mm Hg and that of octane is 420 mm Hg; assume ideal behaviour):
- A.160 mm of Hg
- B.168 mm of Hg
- C.336 mm of Hg✓
- D.350 mm of Hg
The worked solution is part of a paid pack.
ChemistryNEET 2020show ▾The mixture which shows positive deviation from Raoult's law is:
- A.Ethanol + acetone✓
- B.Benzene + toluene
- C.Acetone + chloroform
- D.Chloroethane + bromoethane
The worked solution is part of a paid pack.
ChemistryNEET 2019show ▾For an ideal solution, the correct option (at constant and ) is:
ChemistryNEET 2019show ▾The mixture that forms a maximum-boiling azeotrope is:
- A.Water + nitric acid✓
- B.Ethanol + water
- C.Acetone + carbon disulphide
- D.Heptane + octane
The worked solution is part of a paid pack.
2. Colligative properties
Exam focus: All four colligative properties scale with the number of solute particles, not the solute's identity, which is why every formula carries a van't Hoff factor i. A dissociating electrolyte gives i > 1 and inflates the effect; a solute that associates, like benzoic acid dimerising in benzene, gives i < 1 and shrinks it — the direction of that correction is the usual trap.
Colligative Properties
Aakash NEET
Covers relative lowering of vapour pressure, elevation in boiling point, depression in freezing point and osmotic pressure. Not a primary-preferred channel, but a well-established national coaching brand.
ChemistryNEET 2025show ▾Which of the following aqueous solutions will exhibit the highest boiling point?
- A.0.01 M urea
- B.0.01 M
- C.0.01 M ✓
- D.0.015 M
Solution
Boiling-point elevation depends on the total particle concentration . Urea: . : . : . Glucose: . boils highest.
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Save for spaced revision (free account)ChemistryNEET 2024show ▾The plot of osmotic pressure () vs concentration () for a solution gives a straight line with slope . The temperature at which the osmotic pressure measurement is done is (use ):
- A.310 °C
- B.25.73 °C
- C.12.05 °C
- D.37 °C✓
Solution
, so the slope of against is : K C.
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Save for spaced revision (free account)ChemistryNEET 2021show ▾The following solutions were prepared by dissolving 10 g of glucose () in 250 mL of water (), 10 g of urea () in 250 mL of water () and 10 g of sucrose () in 250 mL of water (). The right option for the decreasing order of osmotic pressure of these solutions is:
ChemistryNEET 2020show ▾The freezing-point depression constant () of benzene is . The freezing-point depression for a solution of molality 0.078 m containing a non-electrolyte solute in benzene is (rounded to two decimal places):
- A.0.20 K
- B.0.80 K
- C.0.40 K✓
- D.0.60 K
The worked solution is part of a paid pack.
3. Abnormal molar mass and van 't Hoff factor
Exam focus: i > 1 means the molar mass calculated from the observed colligative property comes out lower than the true value — dissociation, more particles than expected. i < 1 means it comes out higher — association, like acetic acid dimerising in benzene, fewer particles than expected — and getting which direction the "abnormal" molar mass shifts is exactly what these questions test.
Van 't Hoff Factor and Abnormal Molar Mass
Physics Wallah - Alakh Pandey
Dedicated lecture on van 't Hoff factor and abnormal molar mass (association/dissociation) — exact match.