separating substances

• meaning of pure:

  in chemistry: consists of only one element or compound

  in everyday life: not mixed with anything else
• mixture: consists of two or more different substances, physically combined, can be separated physically
• pure substances have a sharp melting point (straight lines on cooling curve)
• mixtures melt over a range of temperatures (a curve on a cooling curve)
• filtration: used to separate precipitates (insoluble solid) from a liquid

  method:

  • pour solution through filter paper into funnel
  • solvent drips through filter paper but solute (residue) is caught in filter paper
• crystallisation: use to produce solid crystals from a solution

  when solution is warmed, solvent evaporates leaving a more concentrated solute

  method:

  • place solution in evaporating basin
  • heat with bunsen burner until solvent evaporates
  • left with solid crystals of solute
• how pure substances and mixtures change melt