Animations and Videos: Mixtures of Substances

These downloadable videos and animations are part of the multimedia package Stuff and Substance, and are intended to be used to establish the concept of a substance. The individual video and animation files are provided separately here to allow flexibility in their use. The Stuff and Substance multimedia package provides a series of interactive pages that can be used by teachers or students in the classroom, including supporting commentary and questions, animations, videos, images, and teachers’ notes.

Key steps in the development of understanding are:

• Mixtures do not have precise melting and boiling points.
• The difference between boiling and evaporation of water below boiling point: boiling forms a pure sample of water in the gas state (the big bubbles); evaporation below boiling point forms a mixture of water and air.
• On cooling a clear mixture of water and air, water will separate out as droplets in the liquid state.
• Dissolving is recognised by the formation of a clear mixture. Before mixing, solutes can be in the solid, liquid or gas state but the resulting solutions are indistinguishable in terms of particles.
• Solubility is the amount of a substance that will dissolve in a certain amount of solvent. Solubility changes with temperature and a change in solubility can be used to grow crystals. Solubility also depends on the solvent.
• Filtration, evaporation and distillation are methods to separate various types of mixtures.