Q.Explain the following with reason -
🔒You're viewing a preview — the full solution, concept, methods & PYQ mapping are locked.
🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Colloids Classification
Colloids Classification – From Intuition to Precision
Imagine you drop a handful of sand into a glass of water. The sand sinks to the bottom — that's a suspension. Now imagine you stir a drop of milk into water. The milk spreads evenly and never settles. That's a colloid. A colloid is a mixture where one substance is finely dispersed in another, but the particles are too small to settle out and too large to be a true solution.
The key question is: how do we make sense of the endless variety of colloids? The answer is classification — by what is dispersed and what it is dispersed in, and by the nature of the particles themselves.
Classification by Dispersed Phase and Dispersion Medium
Every colloid has two parts: the dispersed phase (the substance that is broken into fine particles) and the dispersion medium (the substance in which those particles are spread). Both can be solid, liquid, or gas. That gives nine possible combinations, but only eight are stable — gas-in-gas is a true solution, not a colloid.
Colloid type=Dispersion mediumDispersed phase
Here is the complete table:
| Dispersed Phase | Dispersion Medium | Common Name | Example |
|---|---|---|---|
| Solid | Solid | Solid sol | Coloured gemstones (e.g., ruby — gold in glass) |
| Solid | Liquid | Sol | Paint, ink, muddy water (fine clay) |
| Solid | Gas | Aerosol (solid) | Smoke, dust in air |
| Liquid | Solid | Gel | Jelly, cheese, butter |
| Liquid | Liquid | Emulsion | Milk, mayonnaise, cream |
| Liquid | Gas | Aerosol (liquid) | Fog, mist, cloud, hair spray |
| Gas | Solid | Solid foam | Pumice stone, foam rubber |
| Gas | Liquid | Foam | Whipped cream, froth on beer |
Notice the pattern: the name often tells you the medium. "Sol" means a liquid medium, "gel" means a solid medium, "aerosol" means a gas medium, "emulsion" means both phases are liquid, and "foam" means gas dispersed in a liquid or solid.
To remember: Aerosol = particles in air (solid or liquid). Emulsion = liquid in liquid. Gel = liquid trapped in a solid network. Sol = solid particles in a liquid.
Classification by Nature of Particles
Colloids can also be grouped by how the dispersed particles interact with the dispersion medium. This is a deeper, chemical classification.
1. Lyophilic colloids (solvent-loving): The dispersed particles have a strong affinity for the dispersion medium. They form spontaneously — just shake gelatin in water and it disperses. These are reversible: if you evaporate the water, the gelatin can be redispersed. Examples: starch, gum, gelatin, proteins in water.
2. Lyophobic colloids (solvent-fearing): The particles have little or no attraction for the medium. They do not form spontaneously — you need special methods (like chemical reactions or mechanical grinding) to make them. They are irreversible: once dried, they cannot be redispersed. Examples: gold sol, silver sol, ferric hydroxide sol, sulphur sol. …
Coagulation destabilises a colloid by neutralising its particles' charge, the Tyndall effect is the scattering of light that makes a beam visible in a sol, and dialysis purifies a colloid by letting small ions diffuse out through a membrane. Each is explained below. …
These three terms describe, respectively, how a colloid is destabilised (coagulation), how it scatters light (Tyndall effect), and how it is purified (dialysis).
- Coagulation: The process of settling (precipitating) the particles of a colloidal sol by neutralising the electric charge that stabilises them, usually brought about by adding an electrolyte. The oppositely-charged ions of the electrolyte neutralise the charge on the colloidal particles, causing them to aggregate into larger particles that settle out. (Example: adding an electrolyte coagulates an As2S3 sol; alum is used to coagulate suspended clay particles in muddy water.)
- Tyndall Effect: The phenomenon in which a beam of light passing through a colloidal solution gets scattered by the colloidal particles, making the path of the light beam visible when viewed from a direction at right angles to the incident beam. This occurs because the size of colloidal particles is comparable to the wavelength of visible light. It is not observed in true solutions, where particles are too small to scatter light. …
Showing the 12 most recent of 17 on this concept.
- CBSE 2026Set A1 markMCQQ.Smoke is a colloidal state in which(a) a gas is dispersed in solid(b) a solid is dispersed in gas(c) a gas is dispersed in gas(d) a liquid is dispersed in gas
›Reveal solutionSolution
Smoke is an aerosol in which solid particles (carbon, ash) are the dispersed phase and a gas (air) is the dispersion medium.
…
- CBSE 2024Set ANNUAL1 markMCQQ.The colloidal system in which the dispersed phase is solid and the dispersion medium is gas is known as -(a) foam(b) gel(c) aerosol(d) emulsion
›Reveal solutionSolution
Colloids are classified by the physical states of their dispersed phase and dispersion medium; solid-in-gas is called an aerosol.
Colloidal systems are named by the combination of dispersed phase and dispersion medium:
Dispersed phase Dispersion medium Name Example Solid Gas Aerosol Smoke Liquid Gas Aerosol Fog, mist Solid Liquid Sol Paints, mud Liquid Liquid Emulsion Milk Gas Liquid Foam Whipped cream Solid Solid Solid sol Coloured glass Gas Solid Solid foam Pumice stone - CBSE 2023Set ANNUAL1 markMCQQ.In the following the Lyophilic colloid is -(a) Milk(b) Gum(c) Blood(d) None of these
›Reveal solutionSolution
Gum is a lyophilic (solvent-loving) colloid.
Lyophilic colloids are those in which the dispersed phase has a strong affinity (liking) for the dispersion medium. Common textbook examples are gum, gelatin, starch, proteins and enzymes dispersed in water — these disperse readily on simple mixing and are self-stabilising and reversible. …
- CBSE 2023Set ANNUAL1 markMCQQ.Which of the following is aerosol?(a) Smoke(b) Soap lather(c) Milk(d) Butter
›Reveal solutionSolution
An aerosol has a gas as the dispersion medium; among the options only smoke (solid-in-gas) fits.
Colloid type depends on the dispersed phase and dispersion medium:
- Smoke: solid dispersed in gas -> aerosol (solid aerosol).
- Soap lather: gas dispersed in liquid -> foam. …
- CBSE 2022Set ANNUAL1 markMCQQ.Which of the following prepare colloidal solution?(a) NaCl(b) Glucose(c) Starch(d) Barium Nitrate
›Reveal solutionSolution
Starch particles are large enough (1 nm - 1000 nm) to form a colloidal sol in water; NaCl, glucose and barium nitrate are small molecules/ions that form true solutions.
A colloid is a heterogeneous, two-phase system in which the size of the dispersed particles lies roughly between 1 nm and 1000 nm - too large to form a true solution but too small to settle out as a suspension. NaCl, glucose and barium nitrate all dissolve in water as individual ions or small molecules (diameter well under 1 nm), so they give true (molecular) solutions, not colloids. Starch, however, is a macromolecule (a polysaccharide of very high molar mass); when dispersed in hot water its huge molecules fall exactly in the colloidal size range, so it forms a …
- CBSE 2022Set ANNUAL1 markMCQQ.Colloidal solution in air is called(a) hydrosols(b) aerosol(c) alcosols(d) aquasols
›Reveal solutionSolution
Colloid names are based on the physical states of the dispersed phase and dispersion medium.
A colloid where the dispersion medium is a gas is termed an aerosol (e.g. smoke = solid particles in air, fog/mist = liquid droplets in air). Hydrosol/aquasol refer to a solid dispersed in water as the medium; alcosol refers t …
- CBSE 2021Set TERM11 markQ.Smoke is a _______ type of Colloidal system.
›Reveal solutionSolution
Smoke is a colloidal dispersion of tiny solid (carbon/soot) particles in air (a gas), which is classified as an aerosol.
Colloidal systems are classified by the physical states of the dispersed phase and dispersion medium. In smoke, tiny solid soot/carbon particles (dispersed phase, solid) are suspended in air (dispersion medium, gas). A colloidal system with solid dispersed i …
- CBSE 2020Set ANNUAL1 markMCQQ.The dispersed phase and dispersion medium in smoke are respectively(a) Gas and liquid(b) Liquid and gas(c) Solid and gas(d) Solid and liquid
›Reveal solutionSolution
Smoke is an aerosol: solid particles (soot, ash) dispersed in a gas (air).
Colloidal systems are classified by the physical state of the dispersed phase and the dispersion medium. Smoke arises from incomplete combustion, releasing tiny solid carbon/soot particles that remain suspended in air. So:
- Dispersed phase = Solid (soot particles)
- Dispersion medium = Gas (air)
This type of colloid (solid in gas) is called an aerosol (specifically a 'solid aerosol', as opposed to fog which is liquid-in-gas).
…
- CBSE 2020Set ANNUAL1 markQ.Write dispersed phase and dispersion medium of dust, a colloidal solution.
›Reveal solutionSolution
A colloid is classified by the physical state of its dispersed phase and its dispersion medium; dust suspended in air is a solid dispersed in a gas.
Dust is made of fine solid particles suspended in air. Matching this to the standard colloid classification:
- Dispersed phase (the substance present in small quantity, in colloidal-sized particles): Solid.
- Dispersion medium (the continuous phase the particles are spread through): Gas (air). …
- CBSE 2020Set ANNUAL1 markMCQQ.Liquid in Liquid colloidal system are called(a) aerosols(b) foams(c) gels(d) emulsion
›Reveal solutionSolution
A liquid dispersed in another liquid gives an emulsion, e.g. milk (fat globules in water) — option (d).
Colloidal systems are classified by the physical states of the dispersed phase and dispersion medium. When the dispersed phase is a liquid and the dispersion medium is also a liquid (the two being essentially immiscible with each other), the system is called an emulsion. Common examples are milk (fat dispersed in water) and cold cream (oil-in-water or water-in-oil types). Aerosols are liquid/solid dispersed in g …
- CBSE 2019Set 56/1/11 markQ.Why are medicines more effective in colloidal state?(OR)What is difference between an emulsion and a gel?
›Reveal solutionSolution
(a) Colloidal medicines have huge surface area → faster absorption, more effective.
(b) Emulsion = liquid dispersed in liquid (flows); gel = liquid held in a solid network (semi-solid).
Part (a): Why medicines are more effective in the colloidal state
Colloidal particles are 1–1000 nm in size, giving an enormous surface-area-to-volume ratio. This large surface area is easily and rapidly absorbed by body tissues and fluids, so the drug is assimilated quickly and completely, raising its bioavailability and effectiveness (e.g. colloidal medicinal preparations such as argyrol and milk of magnesia).
Part (b): Emulsion vs gel
Feature Emulsion Gel Dispersed phase liquid liquid Dispersion medium liquid solid State liquid, flows freely semi-solid, holds shape Example milk, cod-liver oil jelly, cheese, curd - CBSE 2019Set ANNUAL1 markQ.Write dispersed phase and dispersion medium of milk, a colloidal solution.
›Reveal solutionSolution
Milk is an emulsion - tiny droplets of fat are dispersed throughout a continuous aqueous medium.
A colloidal system is described by its dispersed phase (the substance present in small particles) and its dispersion medium (the substance in which those particles are spread). In milk, minute globules of fat (a liquid) are dispersed throughout the watery fluid (also a liquid) that makes up the bulk of milk. Since both phases are liquids, milk is classifie …
🎓Unlock everything free for 14 days
- ✓Full step-by-step solutions
- ✓Concept-first explanations
- ✓Methods, shortcuts & mistakes
- ✓PYQ mapping + timed mock tests
Full access for 14 days. No credit card required.