How can we recognise mixtures? Aims: To know how the boiling points of mixtures, elements and compounds vary To use graphs, tables and bar charts to present experimental results

Melting and boiling points Melting point: –The temperature at which a solid changes into a liquid –The melting point of a substance is also its freezing point Boiling point: –The temperature at which evaporation happens most quickly –At this temperature a liquid can get no hotter (although a gas can)

The melting and boiling points of pure water At precisely 0 ° C pure water will be an equal mixture of water and ice –Slightly above this temperature and all the ice becomes a liquid –Slightly below and all the liquid becomes ice Pure water melts and boils at 100 ° C

Class practical HEAT 1) 100cm 3 water in a 250 ml beaker. 2) Boil water and record its boiling temperature 3) Add 3 spatulas of salt 4) Boil water and record its boiling temperature

Pure elements and pure compounds have precise melting and boiling points –Mixtures do not –Melt and boil over a range of temperatures

Draw a graph of the following data Mass of salt added to 100cm 3 of water/ g Boiling temperature/ ˚C