(b) Elements, Compounds and Mixtures

• Define an element, mixture and compound

  Elements are substances made up of only one type of atom, mixtures have two or more compounds or elements not chemically linked together and compounds are substances with two or more elements chemically combined together
• Explain what is meant by a pure substance

  Substances consisting of only a single element or compound with no other substances in
• Pure solids have a sharp melting point while pure liquids have a sharp boiling point
• Explain why simple distillation is used

  To separate a liquid from a solution
• Describe how simple distillation is carried out

  
  

  • The solution is first heated. The liquid with the lowest boiling point evaporates and vapor travels upwards
  • It is then cooled in the condenser and condenses into a pure liquid which is collected in a beaker
• Explain why fractional distillation is used

  To separate a mixture of various liquids
• Describe how fractional distillation is carried out

  • The liquid solution is placed in a round bottom flask and heated to the temperature of the liquid with lowest boiling point
  • That substance evaporates first and vapor passes through the condenser where it condenses into a pure liquid which is then collected in a beaker
• Explain why filtration is used

  To separate an insoluble solid from a liquid and solid mixture
• Explain how filtration is carried out

  • Filter paper is placed in a filter funnel above a beaker
  • The mixture of liquid and insoluble solid is poured into the filter funnel
  • This allows small particles to pass through as filtrate but not large solid particles so they stay behind as residue
• Explain why crystallization is carried out

  It is used to separate a dissolved solid from a solution when the solid is much more soluble in a hot solvent than a cold
• Describe how crystallization is carried out

  • Pour the solution into an evaporating dish and heat it
  • Once some of the water has evaporated and the solution becomes more concentrated, remove it from heat and leave it to cool
  • The salt should start to form crystals as it becomes insoluble in the cold concentrated solution
  • Filter the crystals out and leave to dry
• Explain why chromatography may be used

  It is used to separate substances with different solubilities in a given solvent
• Describe how chromatography is carried out

  • Draw a pencil line near the bottom of a sheet of chromatography paper
  • Add spots of different dyes to the pencil line and place it in the beaker which holds the solvent. Make sure that the pencil line is slightly higher than the solvent surface so the dyes don’t bleed and dissolve into the solvent
  • The solvent travels up the paper by capillary action and takes the dyes along with it. Different substances have different solubilities so they travel at different rates
• Explain why in chromatography, the pencil line must be drawn in pencil

  Pencil marks are insoluble so it won’t dissolve in the solvent
• In a chromatogram, pure substances produce only one spot on the paper, if two or more substances are the same they will produce identical chromatograms and a mixture separates to show different components as separate spots

  
• Label the apparatus shown in crystallization

  A) Evaporating dish

  B) Beaker

  
• Label the apparatus shown in filtration

  A) Filter paper

  B) Filter funnel

  C) Filtrate

  D) Solution

  
• Label the apparatus in simple distillation

  A) Thermometer

  B) Water out

  C) Condenser

  D) Water in

  E) Pure water

  F) Solution

  G) Vapor

  H) Heat

  
• Label the apparatus in chromatography

  A) Chromatography paper

  B) Unknown dye

  C) Known dyes

  D) Pencil mark

  E) Solvent