Homogeneous & Heterogeneous Mixtures (College Board AP® Chemistry): Revision Note

Homogeneous & Heterogeneous Mixtures

• A mixture is a material that can be separated by physical means into two or more substances

  • For example, dissolving sodium chloride in water gives a mixture whose composition depends on the amount of sodium chloride dissolved

  • This mixture can be separated into its components by the physical process of distillation

• Mixtures are classified into two types:

  • Heterogeneous mixtures: the macroscopic properties (e.g. color, density) depend on where in the mixture the sample is taken

    • For example, a mixture of potassium dichromate and iron filings which can be separated by the use of a magnet

  • Homogeneous mixtures, also called solutions: the macroscopic properties do not vary throughout the sample

    • Air is a homogeneous mixture of about 78% nitrogen and 21% oxygen by volume, plus small amounts of other gases

• A solution is a homogeneous mixture made up of:

  • The substance being dissolved, the solute

  • A medium of dissolution, the solvent

• Solutions exist in three physical states:

  • Solids, e.g. alloys

  • Liquids, e.g. sodium chloride in water

    • Any solution in which the solvent is water is an aqueous solution, whether the solute is ionic (e.g. NaCl) or molecular (e.g. glucose)

  • Gases, e.g. air

• A colloid is similar to a solution in that it appears to be homogeneous like a solution

  • However, it consists of comparatively large particles of one substance dispersed throughout another substance or solution