Topic 9

• Ion


  A charged atom, molecule or particle
• Tests for a specific ion must be unique
• Reason tests for a specific ion must be unique


  Tests are used to identify ions and must be unique so that the test gives an easily observed result which is specific to the ion that is present
• Carrying out a flame test to test for ions

  1. Clean a nichrome wire using hydrochloric acid

  2. Turn the Bunsen burner onto the blue flame

  3. Dip the wire in a solution of the substance being tested

  4. Place the wire in the flame and record the colour
• Flame test result for lithium ions

  Crimson flame
• Flame test result for sodium ions

  Yellow flame
• Flame test result for potassium ions

  Lilac flame
• Flame test result for calcium ions

  Orange-red flame
• Flame test result for copper ions

  Blue-green flame
• Reason for cleaning the wire before a flame test

  To remove any unwanted ions that might obscure the colour of the flame
• Flame test cannot be used when a compound contains a mixture of metal ions
• Reason flame test cannot be used for a mixture of metal ions

  The flame colours of the ions will blend together so the individual flame colours won't be seen meaning the ions can't be identified
• Precipitate


  An insoluble solid suspended in a liquid
• Testing for aqueous metal ions without flame test

  1. Add sodium hydroxide solution to the metal ions

  2. Observe the colour of the precipitate
• Precipitate colour with sodium hydroxide and aluminium ions


  White (initially), re-dissolves with excess NaOH to form colourless solution
• Observation when sodium hydroxide reacts with ammonium ions

  A pungent smelling gas is produced (NH3) which will turn damp red litmus paper blue
• Distinguishing between aluminium and calcium ions

  1. Add excess sodium hydroxide

  2. Both form white precipitates initially

  3. The precipitate from aluminium ions will re-dissolve to form a colourless solution
• Testing for carbonate ions

  1. Add a few drops of HCl to the sample in a test tube

  2. Connect this test tube to a test tube of limewater

  3. If carbonate ions are present, they will react with the acid to produce carbon dioxide which will turn the limewater cloudy when it is bubbled through limewater
• Chemical equation for reaction between HCl and Na2CO3

  Na2CO3 + 2HCl → CO2 + 2NaCl + H2O
• Testing for sulfate ions

  1. Add HCl to remove any CO3^2- ions

  2. Add a couple of drops of barium chloride

  3. If sulfate ions are present a white precipitate of barium sulfate will form
• Chemical equation for reaction between BaCl2 and MgSO4

  BaCl2 + MgSO4 → BaSO4 + MgCl2
• Carrying out a test for halide ions

  1. Add a few drops of nitric acid to react with any carbonate ions

  2. Add a couple of drops of silver nitrate

  3. Observe the colour of the precipitate
• Precipitate colour with silver nitrate and chloride ions


  White precipitate of silver chloride
• Precipitate colour with silver nitrate and bromide ions


  Cream precipitate of silver bromide
• Precipitate colour with silver nitrate and iodide ions


  Yellow precipitate of silver iodide
• Instrumental methods of analysis

  Methods of analysis that use machinery such as mass spectrometry and gas chromatography
• Precipitate formed when silver nitrate is added to a bromide solution


  Cream precipitate of silver bromide
• Precipitate formed when silver nitrate is added to an iodide solution


  Yellow precipitate of silver iodide
• Benefits of using instrumental methods for analysis

  • Accurate
  • Sensitive
  • Quick to carry out
• Flame photometer


  A device used in inorganic analysis to identify or determine the concentration of metal ions
• How flame photometry can be used to identify metal ions

  An emission spectrum is produced by the flame photometer. Each metal ion produces a unique spectrum so comparing the unknown spectrum to reference spectra can identify the ion.
• How flame photometry can be used to determine the concentration of metal ions

  Take readings using a flame photometer of the metal ions at different concentrations. Plot a calibration curve. Take a reading of the unknown sample and compare to the curve.
• Advantage of flame photometry compared to simple flame testing

  Flame photometry can be used to analyse a mixture of ions whereas flame tests can only be used to identify one ion at a time.
• First four alkanes


  • Methane - CH4
  • Ethane - C2H6
  • Propane - C3H8
  • Butane - C4H10
• Bonds formed between carbon and hydrogen atoms in alkanes

  Covalent bonds
• Why alkanes are saturated hydrocarbons


  Saturated - all C-C bonds are single bonds. Hydrocarbon - only contain carbon and hydrogen atoms.
• First four alkenes


  • Ethene - C2H4
  • Propene - C3H6
  • Butene - C4H8
  • Pentene - C5H10
• Why alkenes are unsaturated hydrocarbons

  They are compounds made up of only carbon and hydrogen atoms and they contain double carbon bonds, C=C.
• Functional group


  The group of atoms responsible for the main chemical properties of a compound.
• Functional group in alkenes

  C=C double bond