Mixtures

• What is a pure substance? 


  Consists of only one element or one compound
• A mixture 


  Two or more substances that are not joined together. The substances can be elements, compounds, or both
• How do you separate mixtures?

  Physical processes. These processes do not involve chemical reactions, and no new substances are made.
• Filtration


  A method used to separate an insoluble solid from a liquid using a physical barrier such as paper
• excess 


  A substance is in excess if there is more than enough of it to react with another reactant.
• How does filter paper work? 


  Has tiny holes or pores in it. These are large enough to let small molecules and dissolved ions through, but not the much larger particles of undissolved solid.
• Crystallisation 


  The process of producing crystals from a solution by evaporating the solvent
• Simple distillation 


  Separation method used to separate a solvent from a solution.
• How does simple distillation work? 


   the dissolved solute has a much higher boiling point than the solvent. When the solution is heated, solvent vapour leaves the solution. It moves away and is cooled and condensed. The remaining solution becomes more concentrated as the amount of solvent in it decreases.
• Fractional distillation 


  a mixture of several substances is distilled and the evaporated components are collected as they condense at different temperatures
• Chromatography 


  used to separate different substances dissolved in a liquid.
• How many spots will a pure substance produce on a chromatogram?

  one
• How many spots will an impure substance, or mixture produce on a chromatogram? 


  Two or more
• In chromatography, how can you tell that two substances are likely to be the same?

  • They produce the same number of spots, and are the same colour.
  • The spots travel the same distance up the paper