topic 2

• Describe melting

  Particles gain energy, vibrate faster, forces of attraction decrease, structure breaks down
• Describe freezing

  Freezing is the phase change from a liquid to a solid. For most substances, when a liquid is cooled enough, the molecules slow down and their attraction overcomes their motion. They arrange in orderly positions and freezing occurs.
• Describe condensation

  gas changes into a liquid; bonds form between particles
• Describe boiling

  "Kinetic energy breaks the bonds, potential energy increases and the average molecular separation increases until all liquid molecules become gas molecules"
• Describe distillation

  Heat mixture to first bpt, particles rise and flow into condensing tube to be collected in a beaker
• Describe fractional distillation


  boil to lowest boiling point, gas will rise and condense to be collected in a beaker after condensing in the condensing tube. liquids with higher bpts may also begin to evaporate, but will cool as they go up the fractionating column filled with glass rods. then increase the temperature to the next boiling point. use a thermometer to measure the temperature
• What method is used to separate a solid from a liquid?

  filtration
• How can you crystallize using evaporation?

  pour solution into an evaporation dish, slowly heat until most solvent evaporates to reach the point of crystallisation and leave in a warm place before drying the crystals in a dessicator
• What is the mobile phase in chromatography?

  Where the molecules can move. This is always a liquid or a gas
• What is the stationary phase?

  Where the molecules can't move. It is a solid or a really thick liquid
• How do you calculate the Rf value in chromatography?

  distance moved by solute/distance moved by solvent - to find the distance moved by the solute, you measure from the baseline to the centre of the spot.
• Describe chromatography


  - Draw a baseline near to bottom of paper using pencil (insoluble)

  - put spot of the solute on the baseline

  - dip end of paper into solvent

  - solvent will move up the paper, solute will dissolve and move too

  - how far it moves = how soluble it is, and how attracted it is to the stationary phase

  - work out Rf rate for comparison
• What are the three phases of water treatment?

  filtration (coarse filter) to remove large twigs and solids.

  sedimentation - adding iron or aluminium sulphate to the water to clump together small particles

  fine filter - gravel or sand beds remove fine particles

  chlorination - chlorine is bubbles through to kill harmful bacteria and other microbes