Class 12 Chemistry Chapter 1 Solutions contributes 6 to 8 marks across CBSE Boards and accounts for 3 to 4% of JEE Main Physical Chemistry, making it the highest-weight chapter in the Physical Chemistry block of the 2026-27 NCERT. This page hosts the chapter notes PDF, sub-topic weightage, important derivations, and the latest CBSE 2025 question pattern.
- CBSE Weightage: 6 to 8 marks, usually one short-answer plus one numerical on Raoult's law or colligative properties
- JEE Main Weightage: 3 to 4% (1 to 2 questions per shift on van't Hoff factor, osmotic pressure, or molarity-molality conversion)
- NEET Weightage: 2 to 3 questions per year, mostly colligative properties and concentration units
You can find the complete Notes for Solutions including every derivation, every formula, sub-topic-wise weightage, and CBSE-style worked examples in the article below.
These Notes are curated by subject experts, mapped to the 2026-27 rationalised NCERT, and refined against the last five years of CBSE Board, JEE Main, and NEET papers.
Also Check:
- Solutions Class 12 Chemistry NCERT Solutions
- Solutions Class 12 Chemistry Formula Sheet
- CBSE Class 12 Chemistry Syllabus 2026-27
Solutions Topic-wise Weightage for CBSE Class 12 Chemistry
This table maps every sub-topic to its CBSE frequency across the last five Board cycles. Sub-topics tagged High deserve the first 60% of your revision window; Low ones need just one conceptual pass.
| Sub-topic | Weightage | CBSE Frequency |
|---|---|---|
| Colligative properties and molar mass determination | High | Almost every year (2021, 2022, 2023, 2024, 2025) |
| Raoult's law and ideal/non-ideal solutions | High | 4 out of last 5 years |
| van't Hoff factor and abnormal molar mass | Medium | 3 out of last 5 years |
| Concentration units (molarity, molality, mole fraction) | Medium | 3 out of last 5 years (numerical-only) |
| Henry's law and gas solubility | Medium | 2 out of last 5 years |
| Types of solutions and solubility of solids in liquids | Low | 1 out of last 5 years (1-mark MCQ) |
Solutions Video Walkthrough
Source: Magnet Brains on YouTube
Class 12 Chemistry Chapter 1 Solutions: Full Concept Walkthrough
Each sub-section below stays within the 2026-27 NCERT scope. Worked numericals and one-line tips are placed inline where students typically slip up.
Types of Solutions and Concentration Units
A solution is a homogeneous mixture; the larger component is the solvent. Four units matter: mass percent, mole fraction x , molarity M = nsolute / Vsolution (L) , and molality m = nsolute / msolvent (kg) . Molality is preferred for colligative calculations because it is temperature-independent.
Solubility and Henry's Law
Solid solubility follows "like dissolves like" and rises with temperature for endothermic dissolution. Gas solubility follows Henry's law: p = KH · x . Higher KH means lower solubility. The law explains scuba-diving bends, carbonated-drink fizz, and altitude sickness.
Raoult's Law and Vapour Pressure
For two volatile liquids, Raoult's law gives p1 = p1∘ x1 and p2 = p2∘ x2 . For a non-volatile solute, this reduces to (p1∘ - p1) / p1∘ = x2 -- the form CBSE asks every alternate year.
Ideal and Non-Ideal Solutions, Azeotropes
Ideal solutions obey Raoult's law throughout with Δ Hmix = 0 (n-hexane + n-heptane). Non-ideal solutions show positive deviation (acetone + ethanol) or negative deviation (chloroform + acetone). Azeotropes boil at constant composition: minimum-boiling from large positive deviation, maximum-boiling from large negative deviation.
Colligative Properties
Four properties depend only on the number of solute particles: relative lowering of vapour pressure, Δ Tb = Kb m , Δ Tf = Kf m , and osmotic pressure π = CRT . Osmotic pressure is preferred for biomolecules because dilute solutions give readable values. A 0.001 M solution at 300 K gives about 0.0247 atm -- small but measurable.
van't Hoff Factor and Abnormal Molar Mass
For dissociating solutes (NaCl, K4[Fe(CN)6]) or associating ones (benzoic acid in benzene), the van't Hoff factor i = observed/calculated colligative property. For degree α into n particles, i = 1 + (n-1)α . Plug i into every formula: π = iCRT , Δ Tb = iKb m , Δ Tf = iKf m .
Solutions Important Derivations for Class 12 Boards
These six derivations are the spine of the chapter for CBSE Boards. At least one appears in the Class 12 Chemistry paper every year -- typically as a 3-mark "derive and apply" question that pairs the derivation with a one-step numerical.
- Raoult's law for non-volatile solute: proves (p1∘ - p1)/p1∘ = x2 -- CBSE 2024, 2022, 2021
- Boiling-point elevation and Kb : Δ Tb = Kb m via Clausius-Clapeyron -- CBSE 2025, 2023
- Freezing-point depression and Kf : Δ Tf = Kf m -- CBSE 2024, 2022
- Osmotic pressure and van't Hoff equation: π V = nRT by gas-law analogy -- CBSE 2025, 2023, 2021
- van't Hoff factor and degree of dissociation: i = 1 + (n-1)α -- CBSE 2024, JEE Main 2024 (Jan shift)
- Henry's constant temperature dependence: KH rises with temperature for most gases -- CBSE 2022
How will Collegedunia's Notes Help You with Solutions?
The Collegedunia Notes for Solutions take you from the bare NCERT skeleton to exam-ready depth in a single PDF.
- 2026-27 NCERT Alignment: Every concept matches the current syllabus, with the older "Polymers" and "Surface Chemistry" chapters explicitly flagged as out of scope.
- Worked Numericals on Every Colligative Property: Four full solutions, one per colligative property, with marking-scheme step-tags so you know where the 3 marks come from.
- Expert Verification: Every formula has been cross-checked against the official NCERT textbook and the latest CBSE marking scheme.
- Last-Day Recap Strip: A two-page concentrated recap at the end lists every formula, every constant ( Kb , Kf for common solvents), and the four most-repeated CBSE question stems.
Solutions Most Repeated Questions in CBSE Class 12 Boards
Six PYQ-style stems below cover roughly 70% of what CBSE has asked from this chapter since 2021. Pair each with its derivation from the box above.
Q1 (CBSE 2025, 3 marks). 18 g of glucose is dissolved in 1 kg of water. Find the boiling point. Kb = 0.52 K kg mol-1. Answer: m = 0.1 , Δ Tb = 0.052 K, boiling point = 373.20 K.
Q2 (CBSE 2024, 5 marks). Define osmotic pressure, derive π V = nRT , and find the molar mass when 5 g in 250 mL gives π = 4.92 atm at 27 °C. Answer: Molar mass ≈ 99 g mol-1.
Q3 (CBSE 2023, 2 marks). Why is the boiling point of water lower in the Himalayas than in Mumbai? Reference the vapour-pressure curve.
Q4 (CBSE 2022, 3 marks). Find the van't Hoff factor and degree of dissociation for 0.1 m aqueous K4[Fe(CN)6] , which freezes at -0.84 °C. Kf = 1.86 K kg mol-1.
Q5 (CBSE 2025 + 2021, 3 marks). State Henry's law. Explain aerated-drink bottling and deep-sea-diver bends.
Q6 (CBSE 2024, 2 marks). Distinguish ideal and non-ideal solutions with one example each. State Δ Hmix sign for both.
Solutions Class 12 Chemistry Previous Year Questions Trend
The mini-table below shows the three Solutions topics that have repeated most across CBSE, JEE Main, and NEET in the last five years. The full year-by-year question map with marks tags is canonical on the Collegedunia NCERT Solutions page.
| Topic | Years repeated | Exams |
|---|---|---|
| Boiling-point elevation / freezing-point depression numerical | 2025, 2024, 2023, 2022 | CBSE, JEE Main, NEET |
| van't Hoff factor for ionic solutes | 2025, 2024, 2022 | CBSE, JEE Main |
| Henry's law conceptual / numerical | 2025, 2023, 2021 | CBSE, NEET |
Full year-wise PYQ map: Solutions Class 12 Chemistry NCERT Solutions
Topics Covered in Class 12 Chemistry Chapter 1 Solutions Notes
The Notes PDF maps to the full 2026-27 NCERT scope for Chapter 1. Concepts walked through include types of solutions (solid-liquid, liquid-liquid, gas-liquid), concentration units (mass percent, ppm, mole fraction, molarity, molality) with worked conversions between molarity and molality using solution density, Henry's law with deep-sea diving and altitude-sickness applications, Raoult's law for two-volatile and non-volatile setups, and the four colligative properties (relative lowering of vapour pressure, Δ Tb , Δ Tf , osmotic pressure). The Notes go deeper than the NCERT textbook on positive deviation (ethanol-acetone, minimum-boiling azeotrope), negative deviation (chloroform-acetone, maximum-boiling azeotrope), and the van't Hoff factor with degree-of-dissociation and degree-of-association derivations. Real-world examples include reverse osmosis desalination, antifreeze in car radiators, salt-on-icy-roads, and 0.9% saline as an isotonic IV fluid.
Solutions Glossary for Class 12 Chemistry
Ten terms cover the entire chapter vocabulary. Tape this list to the front of your notebook on Day 1; the CBSE one-mark MCQ stem is almost always a definitional check on one of these.
- Molarity (M): Moles of solute per litre of solution; temperature-dependent.
- Molality (m): Moles of solute per kg of solvent; temperature-independent.
- Mole fraction (x): Moles of one component over total moles; dimensionless.
- Henry's law: Partial pressure of a gas above a liquid is proportional to its mole fraction in solution.
- Raoult's law: Partial vapour pressure equals mole fraction times pure-state vapour pressure.
- Azeotrope: Liquid mixture that boils without composition change at a fixed temperature.
- Colligative property: Property that depends only on the number of solute particles.
- van't Hoff factor (i): Ratio of experimental to calculated colligative property; corrects for dissociation or association.
- Osmotic pressure ( π ): Pressure required to stop net solvent flow across a semipermeable membrane; π = i C R T .
Solutions Top 5 Formulae for Quick Recall
These five formulae cover almost every numerical CBSE has asked since 2021. The complete master table with dimensional checks and the "when to use which" decision tree is on the Collegedunia Formula Sheet.
| Quantity | Formula |
|---|---|
| Molality | m = nsolute / msolvent (kg) |
| Relative lowering of vapour pressure | (p1∘ - p1)/p1∘ = x2 |
| Boiling-point elevation | Δ Tb = i Kb m |
| Freezing-point depression | Δ Tf = i Kf m |
| Osmotic pressure | π = i C R T |
Full master table: Solutions Class 12 Chemistry Formula Sheet
Solutions Common Misconceptions Class 12 Students Carry
Four traps catch even bright students. A single such slip can cost 4 to 5 marks on a 5-marker, so internalise them before the Board paper.
- Mole fraction has no units. Avoid writing "mol/mol" in a CBSE answer.
- Henry's constant KH is inverse to solubility. High KH means the gas dissolves poorly.
- For benzoic acid in benzene, i < 1 . The acid dimerises, so particle count drops below formula count.
- Osmotic pressure uses molar concentration C, not molality. All other colligative formulas use molality.
Solutions Real-World Applications for Class 12 Chemistry
Four modern applications keep coming back on CBSE assertion-reason questions. Memorise the "why" alongside each.
- Reverse osmosis desalination: Sea water is forced through a semipermeable membrane at pressure above its osmotic pressure (~30 atm), leaving salts behind.
- Antifreeze in car radiators: Ethylene glycol depresses water's freezing point to about -36 °C at 50% w/w, preventing engine-block cracking.
- Salt on icy roads: Calcium chloride wins on van't Hoff factor ( i ≈ 3 ) over NaCl, so it melts ice faster at the same mass loading.
- IV fluids: 0.9% NaCl ("normal saline") is isotonic with blood (~7.7 atm at body temperature), so cells neither swell nor shrink.
Solutions Weightage Compared Across Class 12 Chemistry Chapters
The visual below maps the typical CBSE Boards marks distribution across all 10 chapters of the rationalised 2026-27 NCERT Chemistry book, averaged over the last five Board papers.
More Solutions Chemistry Class 12 Resources
NCERT Notes for Class 12 Chemistry: All Chapters
Use this table to jump to the Notes PDF for any other Class 12 Chemistry chapter once you finish Solutions.
| Chapter | Resource |
|---|---|
| Chapter 2 | Electrochemistry Notes |
| Chapter 3 | Chemical Kinetics Notes |
| Chapter 4 | The d- and f-Block Elements Notes |
| Chapter 5 | Coordination Compounds Notes |
| Chapter 6 | Haloalkanes and Haloarenes Notes |
| Chapter 7 | Alcohols, Phenols and Ethers Notes |
| Chapter 8 | Aldehydes, Ketones and Carboxylic Acids Notes |
| Chapter 9 | Amines Notes |
| Chapter 10 | Biomolecules Notes |
Solutions Class 12 Chemistry Notes FAQs
Ques. Where can I download Solutions Class 12 Chemistry Notes PDF?
Ans. You can download the Solutions Class 12 Chemistry Notes PDF directly from this page. Both the Normal and HD versions are available, and both are free. The Notes are written by Collegedunia subject experts and aligned to the 2026-27 NCERT.
Ques. Is this Notes PDF aligned with the 2026-27 NCERT for Class 12 Chemistry?
Ans. Yes. The Notes reflect the current 2026-27 syllabus for Class 12 Chemistry. The older units on Surface Chemistry, p-Block Elements, General Principles of Isolation of Metals, Polymers, and Chemistry in Everyday Life are no longer part of Chapter 1's scope and have been excluded.
Ques. How many pages is the Class 12th Chemistry Solutions Notes PDF?
Ans. The Notes PDF runs approximately 26 pages and covers every sub-topic in Chapter 1 Solutions: types of solutions, concentration units, solubility and Henry's law, Raoult's law, ideal and non-ideal solutions, azeotropes, the four colligative properties, the van't Hoff factor, and worked CBSE-style numericals.
Ques. What is the CBSE weightage of Chapter 1 Solutions for Class 12 Chemistry Boards?
Ans. Chapter 1 Solutions carries 6 to 8 marks in the CBSE Class 12 Chemistry Board exam. Most years see one 3-mark numerical on colligative properties plus one short-answer on Henry's law or Raoult's law.
Ques. Are these Notes useful for JEE Main and NEET 2026 preparation?
Ans. Yes. JEE Main typically asks 1 to 2 questions from Solutions per shift, focusing on van't Hoff factor, osmotic pressure, and molality conversions. NEET asks 2 to 3 questions per year, mostly conceptual on colligative properties. The Notes flag every JEE/NEET-relevant formula.
Ques. Which derivations from Solutions are most important for CBSE Class 12?
Ans. Six derivations carry the chapter: Raoult's law for non-volatile solute, boiling-point elevation, freezing-point depression, the van't Hoff equation for osmotic pressure, the relation between the van't Hoff factor and degree of dissociation, and Henry's law constant's temperature dependence. The Important Derivations Box above lists each with the years it has appeared in CBSE.
Ques. What is the difference between molarity and molality, and why does Solutions Chapter 1 prefer molality?
Ans. Molarity is moles of solute per litre of solution; molality is moles of solute per kilogram of solvent. Molality is preferred for colligative-property calculations because it does not change with temperature, whereas molarity does (solution volume expands or contracts with temperature).
Ques. What are the four colligative properties covered in Class 12 Chemistry Chapter 1 Solutions?
Ans. The four colligative properties are (i) relative lowering of vapour pressure, (p1∘ - p1)/p1∘ = x2 ; (ii) elevation in boiling point, Δ Tb = Kb m ; (iii) depression in freezing point, Δ Tf = Kf m ; and (iv) osmotic pressure, π = CRT . Each depends only on the number of solute particles, not on their chemical identity. For electrolytes, every formula picks up a van't Hoff factor i .
Ques. State Henry's law and give one real-life application.
Ans. Henry's law states that at constant temperature, the partial pressure of a gas above a liquid is directly proportional to its mole fraction in solution, p = KH x . A higher Henry's constant KH means lower solubility. Two canonical applications are aerated soft drinks (CO2 is bottled under pressure to keep it dissolved) and scuba diving (high pressure at depth dissolves more N2 in blood, causing decompression sickness on rapid ascent).
Ques. What is an azeotrope and why does it form?
Ans. An azeotrope is a liquid mixture that boils at a constant temperature with the same composition in liquid and vapour phases, so fractional distillation cannot separate the components further. Minimum-boiling azeotropes (95% ethanol + water) come from large positive deviation; maximum-boiling azeotropes (68% HNO3 + water) come from large negative deviation. The chapter notes derive both cases with vapour-pressure diagrams.
Ques. How does the van't Hoff factor explain abnormal molar mass?
Ans. The van't Hoff factor i corrects every colligative-property formula for solute dissociation or association. i = 1 + (n-1)α for dissociation; i = 1 - (1-1/n)α for association. Observed molar mass = normal molar mass / i . For NaCl with full dissociation, i = 2 , giving an observed molar mass of 29 g mol-1 (half of 58.5). For benzoic acid in benzene, dimerisation gives i = 0.5 and doubles the observed molar mass.
Ques. What is reverse osmosis and how is it used in desalination?
Ans. In normal osmosis, solvent flows from the dilute side to the concentrated side through a semipermeable membrane. Reverse osmosis applies a pressure greater than the osmotic pressure on the concentrated side, pushing solvent the opposite way and leaving solute behind. Commercial RO desalination uses about 30-40 atm on seawater (osmotic pressure roughly 27 atm) to produce potable water; the same principle drives household RO water purifiers.
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