Topic 8- Chemical Analysis

• What is a pure substance in chemistry?

  A substance that only contains one compound or element.
• What can you tell about purity from the boiling or melting point of a substance?

  A pure substance will melt at a specific temperature.

  The further away the melting or boiling point from its actual temperature, the less pure it is.
• What are formulations?

  Mixtures with exact amounts of components.
• What is the formulation of paint?

  Pigments, solvent, binder, additives
• How are formulations used in everyday life?

  Medicine, cleaning products, cosmetics.
• What is the test for chlorine gas?

  Chlorine will bleach litmus paper to turn it white.
• What is the test for oxygen?

  The test for oxygen is the glowing splint test- where the oxygen will relight the glowing splint in the test tube.
• What is the test for hydrogen gas?

  The 'squeaky pop test' where if you hold a burning split over a test tube containing hydrogen a noise will occur.
• What is the test for carbon dioxide gas?

  Bubbling carbon dioxide through limewater which causes the solution to turn cloudy.
• What is the mobile phase in chromatography?

  The solvent- the molecules are able to move
• What is the stationary phase in chromatography?

  Where the molecules are unable to move- the chromatography paper
• What is normally the solvent in chromatography?

  Ethanol or water
• What happens to molecules that have a high solubility in chromatography?

  They spend more time in the mobile phase and move further up the paper in the time.
• What is the result of a chromatography analysis called?

  Chromatogram
• What is the R value in chromatography?

  The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
• What is the formula for the R value?

  Rr= distance travelled by substance

  -----------------------------

  distance travelled by solvent
• What are the common reasons why chromatography is carried out?

  To see if a certain substance is present, separation
• What should the baseline always be drawn in?


  Pencil.
• Chromatography diagram.

  
• What are anions?


  Negatively charged ions.
• What do test for anions often produce?

  Precipitates
• How do you test for carbonates?

  -Putting a sample of solution in a test tube and adding a few drops of dilute acid

  -connect test tube to a test tube of limewater

  -if carbonate is present, carbon dioxide will be released that will turn the limewater cloudy
• How do you test for sulfates?

  -use a pipette to add a few drops of dilute hydrochloric acid followed by a few drops of barium chloride solution

  -is sulfate ions are present, a white precipitate of barium sulfate will form
• How do you test for halides?

  Add a few drops of dilute nitric acid followed by a few drops of silver nitrate solution:

  • chloride = white precipitate of silver chloride
  • bromide = cream precipitate of silver bromide
  • iodide = yellow precipitate of silver iodide
• What do flame tests identify?


  Metal ions
• What colour flame does lithium ions burn with?

  Crimson flame
• What colour flame does sodium ions burn with?

  Yellow flame
• What colour flame does potassium ions burn with?

  Lilac flame
• What colour flame does calcium ions burn with?

  Orange-red flame
• What colour flame does copper ions burn with?

  Green flame
• How do you perform flame tests?


  -clean a platinum wire loop by dipping it in dilute HCL acid and holding it in a blue flame from a bunsen burner until it burns without any colour

  -dip loop into the sample you want to test and put it back into the flame

  -record colour of flame
• What is a problem with the flame tests?


  If the sample contains a mixture of ions then the flames of some metal ions will be hidden by the colours of others (cannot separate colours)
• What do some metals form with NaOH?

  coloured precipitates
• What colour precipitate does calcium form?


  White
• What colour precipitate does copper(II) form?

  blue
• What colour precipitate does iron(II) form?

  green
• What colour precipitate does iron(III) form?

  brown
• What colour precipitate does aluminium form?


  White at first but then redissolves into a colourless solution
• What colour precipitate does magnesium form?

  white
• What is the ionic equation for calcium forming a precipitate?

  Ca 2+ + 2OH- → Ca(OH)2