Pure substances and mixtures

• A mixture contains:

  different types of particles that are not joined together chemically
• pure water should only contain H2O molecules
• A pure substance only contains:


  one type of particle.
• the presence of an impurity usually changes the melting and boiling point
• • pure water will boil at 100°C and freeze at 0°C.
  • if the water has something dissolved in it, eg salt, it will boil at a temperature higher than 100°C and freeze at a temperature lower than 0°C.