Chemical analysis

• A pure substance can be a single element.
• A pure substance can also be a single compound.
• A pure substance is not mixed with any other substance.
• How can we determine if a substance is pure or not?

  1. Measure its melting point.
  2. Measure its boiling point.
• A pure substance melts at a specific fixed temperature.
• A pure substance boils at a specific temperature.
• Impure substances melt and boil over a range of temperatures.
• What is a formulation?


  A complex mixture that has been designed as a useful product.
• Examples of formulations.

  1. Fuels.
  2. Cleaning products.
  3. Paints.
  4. Medicines.
  5. Alloys.
• What does paper chromatography allow us to do?

  Separate substances based on their different solubilities.
• What is a solvent?

  A substance capable of dissolving other substances.
• What is the paper during chromatography?

  The stationary phase as it does not move.
• What is the solvent during paper chromatography?

  The mobile phase as it moves.
• A pure compound produces a single spot in all solvents.
• Why do we draw our starting line in pencil during paper chromatography?

  If we drew the line in pen, the ink would move up the paper with the solvent.
• Benefits of chromatography.


  It can be used to identify unknown substances.
• How do we calculate an Rf value for a substance?

  Distance moved by substance/ distance moved by solvent.
• Several different substances could have similar Rf values so this experiment needs to be repeated with a different solvent
• Testing for hydrogen.

  1. Insert a burning splint into the test tube.
  2. If hydrogen is present we will hear a squeaky pop.
• Testing for oxygen.

  1. Place a glowing splint into a test tube.
  2. if oxygen is present the splint relights.
• Limewater is an aqueous solution of calcium hydroxide.
• Testing for carbon dioxide.

  1. Draw from of gas into a plastic pipette.
  2. Bubble gas through limewater.
  3. If carbon dioxide is present solution turns cloudy.
• Testing for chlorine

  1. Insert damp litmus paper into a test tube.
  2. If chlorine is present the litmus paper will be bleached white.
• One way to identify a metal ion?

  Use a flame test.
• How to carry out a flame test.

  1. Place a small amount of our chemical onto a wire mounted in a handle.
  2. Place the end of the wire into a blue bunsen burner flame.
  3. The colour of the flame allows us to work out the metal ion present.
• What flame test does lithium produce?

  Crimson flame test.
• What flame test does sodium produce?

  Yellow flame.
• What flame test result do we get from potassium?

  Lilac flame.
• What flame test does calcium produce?

  Orange - red flame.
• What flame test does copper produce?

  A green flame.
• Problems with using flame tests.

  1. colour of a flame test is difficult to distinguish.
  2. Sometime sample contains a mixture of metal ions masking true colour of flame.
• What can scientists use instead of flame tests?

  Flame emission spectroscopy.
• Process of flame emission spectroscopy.

  1. Sample of metal ion in solution is placed into a flame.
  2. Light given out is then passed into a spectroscope.
  3. The spectroscope converts the light into a line spectrum.
  4. Lines are specific for each line spectrum.
• What else does flame emission spectroscopy tell us?

  Concentration of a metal ion.
• Flame emission spectroscopy is an instrumental method.
• An instrumental method is carried out using machines.
• Advantages of using instrumental methods.

  1. They are rapid which means we can analyse samples quicker than if we used flame tests.
  2. They are sensitive so they work on the smallest amounts of a tiny metal compound.
  3. They are more accurate than flame tests.
• What happens if we add sodium hydroxide solution to calcium, magnesium or aluminium ions?

  They all produce a white precipitate which means we cannot distinguish between these tests.
• What happens to aluminium if we add excess sodium hydroxide solution?

  Aluminium redissolves.
• What would we use to work out which ion is calcium?


  Flame tests.