Chemical Analysis (Topic 8)

• What is a chemically pure substance?

  a single element or compound, not mixed with any other substance.
• A chemically pure substance will melt and boil at SPECIFIC temperatures.

  • you can test the purity of a substance by measuring the BP/MP
  • The closer to the actual temp, the more pure it is
  • Impurities will lower/increase the BP/MP
• What is a formulation?

  a mixture that has been designed as a useful product containing precise quantities of each component.
• What is an example of a formulation?

  • fuels, cleaning agents, paints, medicines, alloys, fertilisers,foods.
• What does chromatography do?

  it separates mixtures and can give information to help identify substances.
• What is the stationary phase in chromatography?

  The paper (doesn't move)
• What is the mobile phase in chromatography?

  The solvent/liquid (moving part)
• How do you calculate Rf values for chromatography?

  Distance traveled by substance/distance travelled by solvent
• What affects the Rf value?

  affected by the solvent used
• How many spots will a pure substance form in chromatography?

  1
• How do you test for chlorine gas?


  Use damp litmus paper, if present will bleach the paper white (may originally be red as acidic but will bleach)
• How do you test for oxygen gas?

  Place a glowing splint inside a test tube containing oxygen , if O2 is present, the splint will relight
• How do you test for Carbon dioxide gas?

  Bubbling carbon dioxide through an aqueous solution of calcium thyroxine (limewater) causes solution to turn cloudy
• How do you test for hydrogen gas?

  How a burning splint at end of test tube, if a squeaky pop sound, is present
• What is a metal ion?

  Cation ion (POSITIVE +)
• What test is used to detect cations (metal ions)?

  Flame tests
• What colour flame does LITHIUM produce?

  Crimson flame
• What colour flame does SODIUM produce?

  Yellow flame
• What colour flame does POTASSIUM produce?

  Lilac flame
• What colour flame does CALCIUM produce?

  Orange-red flame
• What colour flame does COPPER produce?

  Green flame
• What happens if a sample contains a mixture of metal ions during a flame test?

  Different colours will be present, the actual sample may be masked by the others.
• How do you complete a flame test?

  • Clean a nichrome wire in a bunsen burner
  • Dip wire into sample and hold in flame
• What is used in a metal precipitate test?

  Sodium hydroxide added to solution
• What colour precipitate is formed when sodium hydroxide is added to CALCIUM?

  White
• What colour precipitate is formed when sodium hydroxide is added to COPPER (II)?

  Blue
• What colour precipitate is formed when sodium hydroxide is added to IRON (II)?

  Green
• What colour precipitate is formed when sodium hydroxide is added to IRON (III)?

  Brown
• What colour precipitate is formed when sodium hydroxide is added to ALUMINIUM?

  White at first, dissolves in excess NaOH to form colourless solution
• What colour precipitate is formed when sodium hydroxide is added to MAGNESIUM?

  White
• What is an anion?

  A negative ion (non-metals)
• Testing for anions usually gives precipitates
• How do you test for carbonate ions?

  Add dilute hydrochloric acid (HCl), connect to test tube containing limewater, will turn cloudy if present
• How do you test for sulfates?

  Barium chloride test. Add dilute Hcl and Barium chloride to sample, barium sulfate (white ppt) will form if present
• How do you test for halide ions?

  Silver nitrate solution. add dilute nitric acid (HNO3) and silver nitrate to sample,

  CHLORIDE = white ppt

  BROMIDE = cream PPT

  IODIDE = yellow ppt
• What are the advantages of instrumental methods?

  • accurate
  • Sensitive
  • Rapid
• What is flame emission spectroscopy used for?

  Analysing metal ions in a solution
• How does Flame emission spectroscopy work?

  The sample is put into a flame and the light given out is passed

  through a spectroscope, this is them placed on a spectrum and metal ions can be detected