Matter is anything that has mass and occupies space. It is made of tiny particles that are in constant motion and have spaces between them. The same matter exists in three common states (solid, liquid, gas) that differ in how tightly the particles are held, and it can be classified into pure substances and mixtures, which are separated by simple physical techniques.
- All matter is particulate. The evidence: substances dissolve and diffuse (a drop of ink spreads through water, the smell of incense reaches across a room), showing particles move and intermix.
- Three established characteristics of these particles: they have spaces between them, they are continuously moving (kinetic energy), and they attract one another (intermolecular force). Temperature increases particle motion; pressure brings particles closer.
- Solid: particles are tightly packed with strong forces; fixed shape and fixed volume; nearly incompressible.
- Liquid: particles are less tightly held; no fixed shape (takes the shape of the container) but a fixed volume; flows.
- Gas: particles are far apart with negligible force; neither fixed shape nor fixed volume; highly compressible; exerts pressure on the container walls.
- A fourth state, plasma (ionised gas, as in the Sun, stars and fluorescent tubes), and Bose-Einstein condensate (at near absolute zero) are mentioned beyond the three everyday states.
- Adding or removing heat changes the state at fixed pressure:
- Melting (solid to liquid) at the melting point; freezing / solidification is the reverse.
- Boiling / vaporisation (liquid to gas) at the boiling point; condensation is the reverse.
- Sublimation: solid directly to gas without a liquid stage (camphor, naphthalene, dry ice, iodine).
- During a change of state the temperature stays constant even as heat is supplied; this hidden heat is the latent heat (latent heat of fusion for melting, latent heat of vaporisation for boiling).
- Evaporation is the slow change of a liquid to vapour from its surface at any temperature below boiling. It causes cooling (it draws latent heat from the surroundings), which is why sweating cools the body and why water in an earthen pot stays cool.
- A pure substance has a fixed composition. It is either an element (one kind of atom, cannot be broken down chemically, for example oxygen, gold, iron) or a compound (two or more elements chemically combined in a fixed ratio, with new properties, for example water, common salt).
- A mixture contains two or more substances physically mixed in any proportion, each keeping its properties.
- Homogeneous mixture (solution): uniform throughout (salt in water, air, alloys). A solute dissolves in a solvent; concentration is the amount of solute in a given solvent.
- Heterogeneous mixture: non-uniform (sand in water, oil in water).
- A colloid (milk, fog) and a suspension (chalk in water) lie between true solutions and coarse mixtures; the Tyndall effect (scattering of a light beam) reveals colloids.
The technique depends on the difference in properties:
- Filtration: separates an insoluble solid from a liquid (sand from water).
- Evaporation: recovers a dissolved solid from its solution (salt from sea water).
- Distillation: separates a liquid from a solution, or two miscible liquids of different boiling points (fractional distillation separates the components of crude petroleum and of liquefied air).
- Sublimation: separates a sublimable solid (ammonium chloride, camphor) from a non-sublimable one.
- Chromatography: separates dissolved substances that travel at different rates (the dyes in ink).
- Centrifugation: separates fine suspended particles using spin (cream from milk, in diagnostic labs).
- Separating funnel: separates two immiscible liquids (oil and water).
- Magnetic separation: removes magnetic material (iron filings) from a mixture.
- Matter: anything with mass and volume; particulate.
- Latent heat: the heat absorbed or released during a change of state at constant temperature.
- Evaporation: surface vaporisation below boiling, causing cooling.
- Element, compound, mixture: one atom type; chemically combined; physically mixed.
- Tyndall effect: scattering of light that reveals a colloid.
Separation and purification underlie water treatment (filtration, distillation, reverse osmosis), a public-health and field-logistics concern for deployed forces. Sublimation and evaporation explain field-craft such as keeping water cool in earthen pots and the action of cooling. Knowledge of states of matter underpins handling of compressed gases and cryogenics in defence applications.
- The slow change of a liquid into vapour from its surface at any temperature, which causes cooling, is called: (a) boiling (b) sublimation (c) evaporation (d) condensation. (Answer: c.) Authored practice, not a verbatim PYQ.
- Which technique would best separate two miscible liquids with different boiling points? (Answer: fractional distillation.) Authored practice, not a verbatim PYQ.