Matter and Materials
What you must understand
Matter has mass and occupies space. Candidates must describe the particle model of solids, liquids and gases, and use it to explain diffusion, compression, expansion and changes of state. Know the terms melting, freezing, evaporation, condensation, sublimation and deposition, and that these changes are physical, not chemical. Understand mixtures and how to separate them: filtration, evaporation, distillation, magnetism, sieving and decanting. Know the difference between an element, a compound and a mixture, and recognise common elements by symbol. Understand density as mass per unit volume and that heating usually expands matter, lowering its density.
Traps that appear in questions
- Saying particles expand when heated; the particles stay the same size, they move faster and spread further apart.
- Calling dissolving a chemical change; dissolving is usually physical and reversible by evaporation.
- Thinking gases have no mass.
- Confusing distillation (separates a dissolved solid from liquid, or two liquids by boiling point) with filtration (separates an insoluble solid).
- Forgetting that mass is conserved in a change of state, even though volume may change.
- Writing density units incorrectly; density is g/cm³ or kg/m³.
Rule of thumb and worked example
Choose the separation method by asking: is the solid dissolved? If no, filter it. If yes, evaporate or distil the liquid.
Example: A block has mass 240 g and volume 30 cm³. Density = mass ÷ volume = 240 ÷ 30 = 8 g/cm³. This is denser than water (1 g/cm³), so the block sinks. Always show the formula, substitute with units, then state the answer with units.