Elements, compounds and mixtures 2

Elements, compounds and mixtures 2

1. distillation

   • separates a solvent from a solution
     • solvent has a much lower boiling point that the solute
   • the solution is heated and the solvent boils but the solvent doesn't
     • the solvent escapes from the solution in its gas state
       • then it os cooled and condensed back to its liquid state by a condenser

2. Chromatography

   • relies on two different chemical phases
     • stationary phase that doesn't move
     • mobile phase that does move
     • paper chromatography
       • the stationary phase is the absorbent paper
       • the mobile phase is a solvent in the liquid state
     • Thin layer chromatography
       • the stationary phase is a thin layer of silica or alumina powder spread over a plate of glass or plastic
       • the mobile phase is a solvent in the liquid state
     • gas chromatography
       • the stationary phase is silica or alumina powder packed into a metal column
       • the mobile phase is an unreactive carrier gas that does not react with the sample

3. calculating an Rf value

   • distance travelled by substance/distance travelled by solvent

4. purification and checking purity

   • use paper or thin layer chromatography
     • to tell if its pure
       • paper/thin layer
         • only one substance is revealed
       • gas
         • only of substance is detected or revealed