Solutions Notes for NEET and JEE Main 2027: Key Points and PDF

Solutions is Chapter 1 of NCERT Class 12 Chemistry Part I and forms Unit 5 of Physical Chemistry in both the NEET UG and JEE Main syllabus. These notes cover concentration terms, solubility and Henry’s law, Raoult’s law, ideal and non-ideal solutions, azeotropes, the four colligative properties and the van’t Hoff factor, with a free notes PDF.

Solutions Notes for NEET and JEE Main

Section-wise key points from NCERT Chapter 1, formula and comparison tables, high-yield facts and common mistakes for 2027 revision.

Solutions at a Glance

The topic list follows the NEET UG 2026 syllabus (NMC public notice dated 22 December 2025) and the JEE Main 2026 syllabus published by NTA, which stay the reference until the 2027 versions are out. The full lists are on the NEET syllabus and JEE Main syllabus pages. Henry’s law, azeotropes and reverse osmosis are in the NCERT chapter but are not named separately in the syllabus text.

What is a solution and what types are there?

A solution is a homogeneous mixture of two or more components; the component present in the largest amount is usually the solvent, and it decides the physical state of the solution.

• Brass is copper + zinc, German silver is copper + zinc + nickel, and bronze is copper + tin.
• 1 ppm fluoride in water prevents tooth decay, while 1.5 ppm causes mottled teeth.

How is the concentration of a solution expressed?

Mass percentage, ppm, mole fraction and molality do not depend on temperature; molarity does, because volume changes with temperature.

Solubility and Henry’s Law

Solubility is the maximum amount of a substance that dissolves in a specified amount of solvent at a given temperature; for gases, Henry’s law links it to pressure.

• ‘Like dissolves like’: polar solutes dissolve in polar solvents and non-polar solutes in non-polar solvents.
• A saturated solution is in dynamic equilibrium with undissolved solute (dissolution and crystallisation at equal rates).
• Solid in liquid: if dissolution is endothermic, solubility rises with temperature; if exothermic, it falls (Le Chatelier). Pressure has no significant effect, since solids and liquids are nearly incompressible.
• Gas in liquid: solubility increases with pressure and decreases with temperature, because dissolving a gas is exothermic.
• Henry’s law: at constant temperature the solubility of a gas is proportional to its partial pressure; commonly p = KH x.
• A higher KH means lower solubility. KH of N2 and O2 rises with temperature, which is why aquatic species are more comfortable in cold water.

Vapour Pressure and Raoult’s Law

Raoult’s law: for a solution of volatile liquids, the partial vapour pressure of each component is directly proportional to its mole fraction in the solution.

• p1 = p1° x1 and p2 = p2° x2, where p° is the vapour pressure of the pure component.
• Dalton’s law: ptotal = p1 + p2 = p1° + (p2° − p1°) x2, so ptotal varies linearly with x2.
• Vapour composition: pi = yi ptotal. The vapour is always richer in the more volatile component.
• NCERT example: CHCl3 (200 mm Hg) and CH2Cl2 (415 mm Hg) at 298 K give ptotal = 347.9 mm Hg, with y(CH2Cl2) = 0.82 in the vapour.
• Raoult’s law is a special case of Henry’s law in which KH equals p1°.
• A non-volatile solute lowers the vapour pressure of the solvent, because solute particles occupy part of the surface. The lowering depends on the amount of solute, not its nature: 1 mol sucrose and 1 mol urea in 1 kg water give nearly the same lowering.
• Raoult (French chemist) gave the law in 1886.

What is the difference between ideal and non-ideal solutions?

Ideal solutions obey Raoult’s law at all concentrations; non-ideal solutions show positive or negative deviations depending on whether A–B attractions are weaker or stronger than A–A and B–B.

• Azeotropes are binary mixtures with the same composition in liquid and vapour that boil at constant temperature, so they cannot be separated by fractional distillation.
• Minimum boiling example: ethanol-water; fractional distillation stops at about 95% ethanol by volume.
• Maximum boiling example: nitric acid-water, about 68% HNO3 and 32% water by mass, boiling at 393.5 K.

Colligative Properties and Molar Mass

Colligative properties depend on the number of solute particles relative to the total, not on their identity: relative lowering of vapour pressure, elevation of boiling point, depression of freezing point and osmotic pressure.

• Kb (ebullioscopic constant) and Kf (cryoscopic constant) have the unit K kg mol–1 and depend only on the solvent: Kf = R M1 Tf² ÷ (1000 ΔfusH) and Kb = R M1 Tb² ÷ (1000 ΔvapH).
• Water: Kb = 0.52 and Kf = 1.86 K kg mol–1. Benzene: Kb = 2.53 and Kf = 5.12 K kg mol–1 (NCERT Table 1.3).
• A solution of 1 mol sucrose in 1000 g water boils at 373.52 K at one atmosphere.
• A solution freezes when its vapour pressure equals that of the pure solid solvent, which happens at a lower temperature.

Osmosis, Osmotic Pressure and Reverse Osmosis

Osmosis is the flow of solvent through a semipermeable membrane from pure solvent (or dilute solution) into the more concentrated solution; osmotic pressure is the excess pressure that just stops it.

• Semipermeable membranes may be natural (pig’s bladder, parchment) or synthetic (cellophane).
• Osmotic pressure is the preferred method for molar masses of proteins, polymers and other macromolecules: it is measured near room temperature, uses molarity, and is large even for very dilute solutions.
• Isotonic solutions have the same osmotic pressure; no osmosis occurs between them.
• Blood cell fluid is isotonic with 0.9% (mass/volume) NaCl, called normal saline. Above 0.9% (hypertonic) cells shrink; below 0.9% (hypotonic) they swell.
• Everyday examples: raw mangoes shrivel in brine, wilted flowers revive in fresh water, salty food causes edema, and salting meat or sugaring fruit kills bacteria by osmosis.
• Reverse osmosis: a pressure larger than the osmotic pressure pushes pure solvent out of the solution. It is used to desalinate sea water with a cellulose acetate membrane, which lets water through but not ions and impurities.

Abnormal Molar Masses and the Van’t Hoff Factor

Dissociation increases the number of particles and gives a lower experimental molar mass; association reduces it and gives a higher one. The van’t Hoff factor i corrects for this.

• i = normal molar mass ÷ abnormal molar mass = observed colligative property ÷ calculated colligative property = total moles of particles after ÷ before association or dissociation.
• Van’t Hoff introduced the factor in 1880.
• i > 1 for dissociation (KCl in water is close to 2); i < 1 for association (ethanoic acid in benzene is nearly 0.5, because it dimerises by hydrogen bonding in a solvent of low dielectric constant).
• Modified equations: ΔTb = i Kb m, ΔTf = i Kf m, Π = i n2RT/V, and relative lowering of vapour pressure = i n2/n1.

Most-asked Facts for NEET and JEE Main: Solutions

Revise these one-line facts from the NCERT chapter just before the exam.

• Molarity depends on temperature; molality, mole fraction, mass % and ppm do not.
• Henry’s law: p = KH x; higher KH means lower gas solubility.
• Gas solubility in liquids falls as temperature rises.
• Scuba tanks: 11.7% He, 56.2% N2, 32.1% O2 to avoid bends.
• Raoult’s law for a non-volatile solute: relative lowering of vapour pressure = mole fraction of solute.
• Ideal solution: ΔmixH = 0 and ΔmixV = 0; e.g. benzene + toluene.
• Positive deviation: ethanol + acetone; negative deviation: chloroform + acetone, phenol + aniline.
• Large positive deviation gives a minimum boiling azeotrope (ethanol-water, about 95% ethanol).
• Large negative deviation gives a maximum boiling azeotrope (HNO3-water, 68% HNO3, 393.5 K).
• Kb of water = 0.52 K kg mol–1; Kf of water = 1.86 K kg mol–1.
• Π = CRT; osmotic pressure is used for molar masses of proteins and polymers.
• 0.9% (mass/volume) NaCl is normal saline, isotonic with blood cells.
• Reverse osmosis uses a cellulose acetate membrane to desalinate sea water.
• i is close to 2 for KCl in water and nearly 0.5 for ethanoic acid in benzene.
• Dissociation lowers, association raises the experimentally found molar mass.

Common Mistakes to Avoid

Watch for these mix-ups when you answer questions on this chapter.

• Using litres of solution for molality. Molality uses kilograms of solvent; molarity uses litres of solution.
• Thinking a larger Henry’s law constant means higher solubility. It means lower solubility.
• Saying gas solubility increases with temperature. It decreases, since dissolution of a gas is exothermic.
• Swapping the azeotrope types: positive deviation gives a minimum boiling azeotrope, negative deviation a maximum boiling one.
• Calling chloroform + acetone a positive deviation. Hydrogen bonding between them makes it negative.
• Using molality in the osmotic pressure formula. Π = CRT uses molarity.
• Writing i > 1 for association. Association gives i < 1 and a higher apparent molar mass.
• Saying the vapour above a solution has the same composition as the liquid. It is richer in the more volatile component (except for an azeotrope).
• Mixing up hypertonic and hypotonic: cells shrink in a hypertonic solution (above 0.9% NaCl) and swell in a hypotonic one.

Solutions Notes PDF and Related Pages

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• All chapters: Chemistry notes for NEET and JEE Main
• Full topic list: NEET syllabus and JEE Main syllabus
• Practice: NEET question papers and JEE Main question papers
• Source text: NCERT Chapter 1 (NCERT, Class 12 Chemistry Part I)

Chemistry Notes for NEET and JEE Main: All Chapters

• Some Basic Concepts of Chemistry
• Structure of Atom
• Chemical Kinetics
• Equilibrium
• Organic Chemistry: Some Basic Principles and Techniques
• Electrochemistry
• Amines
• Solutions
• Thermodynamics
• Coordination Compounds
• Haloalkanes and Haloarenes
• p-Block Elements
• Alcohols, Phenols and Ethers
• Hydrocarbons
• Aldehydes, Ketones and Carboxylic Acids

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