Mixtures

• What is the definition of a mixture?

  A mixture consists of two or more elements or compounds that are not chemically combined together.
• Are chemical properties of each substance in the mixture changed or unchanged?

  Unchanged
• State the 5 physical processes used to separate mixtures.

  • Filtration
  • Crystallisation
  • Simple Distillation
  • Fractional Distillation
  • Chromatography
• What is filtration used to separate and give an example.

  • Used to separate an insoluble solid from a liquid
  • For example, sand from water
• What is crystallisation used to separate and give an example.

  • Used to separate a soluble solid from a solution
  • For example, salt from saltwater
• What is simple distillation used to separate and give an example.

  • Used to separate a solvent from a solution
  • For example, pure water from seawater
• What is fractional distillation used to separate and give an example.

  • Used to separate two or more liquids with different boiling points
  • For example, seperating ethanol from water
• What is chromatography used to separate and give an example.

  • Used to seprate different substances dissolved in a solvent
  • For example, separating dyes in ink
• Explain the steps of filtration.

  1. One beaker contains a mixture of solid and liquid, the other contains a funnel with filter paper
  2. The solid and liquid mixture is poured into the filter funnel
  3. The liquid drips through the filter paper but the solid particles are caught in the filter paper
• Explain the steps of crystallisation.

  1. A solution is placed in an evaporating basin and heated with a Bunsen burner.
  2. The volume of the solution has decreased because some of the water has evaporated. Solid particles begin to form in the basin.
  3. All the water has evaporated, leaving solid crystals behind.
  4. Filter out the crystals using filter paper and dry them.
• Explain the steps of simple distillation.

  1. Salt solution is heated.
  2. Water evaporates and its vapours rise. The water vapour passes into the condenser, where it cools and condenses. Liquid water drips into a beaker.
  3. All the water has evaporated from the salt solution, leaving the salt behind.
• Explain the steps of fractional distillation.

  1. A water and ethanol mixture is heated in a flask using an electric heater. Vapour forms in the air above the mixture in the flask
  2. The boiling point of ethanol is 78°C. Ethanol vapour passes into the condenser, where it is cooled and condensed. Liquid ethanol drips into a beaker.
  3. When most of the ethanol has left, water vapour at 100°C passes into the condenser, where it is cooled and condensed. Liquid water now drips into a second beaker.
• Explain the steps of chromatography.

  1. A pencil line is drawn, and spots of ink or plant dye are placed on it. There is a container of solvent, such as water or ethanol.
  2. The paper is lowered into the solvent. The solvent travels up through the paper, taking some of the coloured substances with it.
  3. As the solvent continues to travel up the paper, the different coloured substances spread apart. In this example, the separated coloured substances are yellow, red and black.