2.3 Chemical analysis

• What is a pure substance?


  a substance made from only one element or compound
• what are characteristics of a pure substance ?

  • contains no other chemicals
  • has a fixed melting and boiling point
• examples of pure substances?

  copper sulfate, distilled water
• what are not examples of pure substances?

  • air
  • crude oil
  • fractions ( eg. petrol , diesel )
• what is a formulation?


  a formulation is a mixture of substances that follow a particular recipe
• characteristics of a formulation?

  • consistent in taste or dosage
  • mixture of substances in a set ratio
• Examples of formulation

  • drinks
  • drugs / pharmaceuticals
  • cosmetics
  • paint
• Non- examples of formulation?

  • pure substances
  • squash
  • home cooking
  • honey
• how do you produce pure water?

  by distillation
• what are the gases that can be tested for

  1. Hydrogen
  2. Carbon dioxide
  3. Oxygen
  4. Chlorine
• Describe the test for hydrogen

  1. Collect gas in a test tube
  2. Light/ hold a lit splint at the end of test tube
  3. If hydrogen is present there is a squeaky pop!
• Describe the test for carbon dioxide

  1. bubble carbon dioxide through lime water ( Ca(OH)2)
  2. carbon dioxide would turn lime water cloudy
• Describe the test for oxygen

  Glowing splint relights

  1. Lit a splint
  2. blow out the lit splint
  3. if Oxygen is present, the splint would relight
• Describe the test for Chlorine


  bleaches damp litmus paper and makes it white
• What safety precautions are required for testing chlorine gas?

  Wear a gas mask and do the experiment in a fume cupboard
• How to rest for carbonate ions?

  1. React the substance with hydrochloric acid (HCl).
  2. If the substance contains a carbonate ion, carbon dioxide gas will bubble out of the solution. 
  3. Collect the gas and bubble it through limewater.
  4. If the limewater turns cloudy, it confirms the gas is carbon dioxide.
• How to test for Sulfate ions?

  1. Add dilute hydrochloric acid then
  2. Add barium chloride solution.
  3. If sulfate ions are present, it will form a white precipitate of barium sulfate.
• How to test for halide ions?

  1. Add dilute nitric acid then
  2. Add silver nitrate solution

  chloride gives white precipitate

  bromide gives a cream precipitate

  iodide gives yellow percipitate
• What is anions


  Negatively charged ion
• What is cations


  Positively charged ion
• Test for cations (metal ions)

  1. Flame test
  2. The metal hydroxide tests
• steps for flame test

  1. Dip clean wire loop into a solid sample of compound being tested
  2. Put loop into the edge of the blue flame from a Bunsen burner
  3. Observe flame colour produced.
• What is the limitations for flame test?

  It would be difficult to recognise the metal present if sample tested has 2 or more metals as the colour of the flame would be combined
• Flame test for lithium ion


  Crimson flame
• Flame test for sodium ion


  yellow ion
• Flame test for potassium ion


  Lilac flame
• flame test for calcium ion


  orange-red flame
• flame test for copper ion


  green flame
• Metal hydroxide test:

  1. React sample with a solution of sodium hydroxide
  2. See the colour solution of sample turns to
• metal hydroxide test for calcium ion

  white precipitate
• Metal hydroxide test for iron (II)

  Green precipitate
• Metal hydroxide test for Iron (III)

  Brown percipitate
• Metal hydroxide test for Aluminium (II)

  White to colourless
• Metal hydroxide test for Magnesium

  White precipitate
• Metal hydroxide test for Copper (II)

  Blue precipitate
• What are instrumental methods?

  they are accurate, sensitive and rapid methods which are useful when the amount of sample is very small
• How is Rf calculated?

  Rf=distance moved by the spot / distance moved by solvent
• What is the mobile phase in paper chromatography?

  Solvent (Water)
• What is the stationary phase in paper chromatography?


  Paper
• What happens to a substance that is more soluble in the mobile phase?

  It will move faster through the chromatography system and travel further distance up the paper