Analysing and identifying substances

• What is a pure substance?

  Consists of one element or one compound only.
• What is a mixture?

  Consists of two or more different substances that are not chemically combined together.
• What is a compound?

  Contains two or more type of atom joined together
• Give an example of a pure element

  Oxygen
• Give an example of a pure compound

  Carbon dioxide
• Give an example of a mixture of elements

  Oxygen and Helium
• Give an example of a mixture of compounds

  Alcohol and water
• Give an example of a mixture of elements and compounds

  Air
• Pure substances have a..

  Sharp melting point
• Mixtures can melt over a..

  Range of temperatures
• What happens to the temperature of a pure substance changes state?


  It stays the same
• What happens to the temperature in an impure substance?

  Gradually falls
• What is a formulation?

  A mixture which has been designed as a useful product
• Give 3 examples of a formulation:

  • Fuels
  • Cleaning products
  • Paints
• What is paper chromatography?

  A method used to separate mixtures of soluble substances which provides information on the possible identity of substances present in the mixture
• What is the ’mobile’ phase in chromatography?

  The solvent that moves through the paper
• What is the ‘stationary’ phase in chromatography?


  Contained on the paper and does not move through it
• How many spots does a pure substance produce on a chromatogram?


  One spot
• How many spots does an impure substance produce on a chromatogram?

  Two or more
• How can you tell if two substances are the same on a chromatogram?


  • They produce the same number of spots which match in colour
  • The spots travel the same distance up the paper
• How is the Rf spot calculated?

  Distance travelled by substance/Distance travelled by solvent
• State a method to investigate how paper chromatography can be used to seperate and tell between different coloured substances

  1. draw a pencil line across the chromatography paper, 1 - 2 cm from the bottom
  2. use a pipette or capillary tube to add small spots of each ink to the line on the paper
  3. place the paper into a container with a suitable solvent in the bottom
  4. allow the solvent to move through the paper, but remove the chromatogram before it reaches the top
  5. allow the chromatogram to dry, then measure the distance travelled by each spot and by the solvent
• Why will measurements in mm give more precise Rf values?

  As they are more precise than in centimetres
• How can you tell if oxygen is present in a test tube?

  A glowing splint relights when it is held inside
• How can you tell if hydrogen is present in a test tube?

  A lighted splint ignites with a squeaky pop
• How can you tell if carbon dioxide is present in a test tube

  Limewater turns cloudy or milky white
• How can you tell if chlorine is present in a test tube?

  Damp litmus paper turns white