Matter, Materials and Their Properties
This domain tests the particle model of solids, liquids and gases, changes of state, everyday properties of materials, and how mixtures are separated.
States and the particle model
In a solid, particles are closely packed and vibrate in fixed positions, giving a fixed shape and volume. In a liquid, particles are close but slide past each other, giving a fixed volume but no fixed shape. In a gas, particles are far apart and move quickly, so a gas fills its container. Heating gives particles more kinetic energy, which is why solids melt and liquids boil. Mass is conserved during changes of state; water expands when it freezes, so ice floats.
Properties and mixtures
Materials are chosen for hardness, strength, flexibility, conductivity, magnetism, solubility and transparency. Dissolving is not melting: sugar stirred into water disappears into the liquid without forming a new substance. Mixtures can be separated by hand sorting, sieving, magnetism, filtration (insoluble solid from liquid), decanting, and evaporation or crystallisation (dissolved solid from solution).
Worked example
Separate a mixture of salt and sand. Add water and stir so the salt dissolves; filter, and the sand stays on the filter paper while salt solution passes through. Wash and dry the sand, then gently evaporate the filtrate to leave salt crystals. Filtration alone cannot remove salt because dissolved particles pass through the filter.
Traps that cost marks
Gases do have mass. Particles in ice still vibrate - they are not completely still. Condensation is water vapour cooling into droplets, not 'air turning into water'. A colour change during dissolving is not proof of a chemical change.