Junior Cert Science - Mixtures

Mixtures

  • A mixture consists of two or more elements which are mixed together but are not chemically combined.
  • Examples of mixtures are air (a mixture of gases) and seawater (a mixture of water & salt).
  • Crystillisation is when crystals are formed from a solution which is evaporated.

Separating Mixtures

  • Filtration is used to separate insoluble solids from liquids. The mixture is passed through filter paper, which traps the solids and allows the liquid to pass through.
  • Evaporation is used to separate soluble solids from liquids. The liquid is evaporated, leaving the solid behind.
  • Distillation is used to separate two liquids with different boiling points, e.g. water and alcohol. It can also be used to separate soluble solids from liquids.
  • Chromotography is used to separate a mixture of dissolved substances in a solution.

Solutions

  • A solution is a mixture of a solute (substance which is dissolved) and a solvent (liquid in which the solute is dissolved), e.g. copper sulfate dissolved in water.
  • The hotter the solvent, the more solute will dissolve in it.
  • A concentrated solution has a large amount of solute dissolved in a small amount of solvent. A dilute solution has a small amount of solute dissolved in a large amount of solute.
  • A saturated solution is one which has the maximum possible amount of dissolved solute at that temperature.
  • A dilute solution can be made concentrated by adding more solute or evaporating off some of the solvent. A concentrated solution can be made more dilute by adding more solvent.
  • When a saturated solution is cooled to a lower temperature, crystals of the solute form. This is known as crystallisation. For example, when a concentrated solution of copper sulfate in water is cooled, copper sulfate crystals form.