Matter and Its Nature: States, Classification, and Separation
This domain tests how well you can describe the states of matter, classify a substance as an element, compound, or mixture, and choose a separation method from the physical property that differs between components.
Core rules
- Solids have fixed shape and volume; liquids have fixed volume but take the shape of the container; gases fill the container. Changing state involves heat exchange, not a change in chemical identity.
- A pure substance has a fixed composition. An element contains one kind of atom; a compound contains two or more elements chemically combined in a fixed ratio. A mixture contains substances not chemically combined and can be separated by physical methods.
- Separation depends on a difference in property: particle size for filtration, boiling point for distillation, solubility for evaporation or crystallisation, magnetism for magnetic materials, sublimation for substances such as camphor or ammonium chloride, and adsorption on a stationary phase for chromatography.
Worked example
Separate a mixture of iron filings, common salt, and sand. Move a magnet through the mixture: iron is magnetic and is removed. Add water and stir: salt dissolves, sand does not. Filter: sand stays on the filter paper as residue, salt solution passes through as filtrate. Evaporate the filtrate carefully to recover salt. Each step uses a different property, so the order matters.
Traps that cost marks
Do not call a compound a mixture because it contains two elements; a compound has a fixed ratio and new properties. Do not use evaporation when a heat-sensitive solid such as sugar must be recovered; crystallisation is safer. Remember that distillation separates miscible liquids with different boiling points, while a separating funnel is for immiscible liquids.
Key points
- Classify first, then select a method based on a property difference.
- Filtration separates an insoluble solid from a liquid.
- Distillation uses boiling-point difference and can recover both components.
- A compound can be broken down only by chemical means.