Matter and Its Nature
Matter and Its Nature examines the particle model of matter, the three common states, interconversion of states, and how pure substances differ from mixtures. Questions often ask you to choose a separation method or explain a change in terms of particles.
Core ideas
- Matter is made of particles with space between them; particles move faster at higher temperature.
- Solids have fixed shape and volume, liquids fixed volume but not shape, gases neither.
- Interconversion: melting, freezing, evaporation, condensation, sublimation, deposition. Latent heat is absorbed or released without a temperature change during a state change.
- A pure substance has a fixed composition: an element (one kind of atom) or a compound (elements chemically combined). A mixture can be separated by physical methods.
- Separation depends on a property difference: magnetism (iron), sublimation (camphor or ammonium chloride), filtration (insoluble solid), distillation (miscible liquids with different boiling points), chromatography (dyes).
Worked example
Separate a mixture of iron filings, camphor and common salt. Hold a magnet over the mixture to remove iron. Heat the rest gently: camphor sublimes and is collected by condensation; salt remains. Dissolve the salt in water and evaporate to recover it. Reasoning: each step uses a different physical property, and no new substance is formed.
Traps that cost marks
Sublimation is solid-to-gas directly; evaporation is liquid-to-gas. A compound cannot be separated by filtration. In a chemical change the identity changes; in a physical change it does not. Do not say particles expand when a gas is heated; they move faster and the spacing increases.