*Developing Metals

• A redox reaction is a reaction in which both oxidation and reduction occur
• Method for balancing equations:

  1. Balance all atoms except hydrogen and oxygen
  2. Add H2O to balance oxygens
  3. Add H+ ions to balance hydrogens
  4. Add e- to balance charges
• In redox titration between iron and manganate ions the iron ions are oxidised and manganate ions are reduced
• The end point of the redox titration between iron and manganate ions is a pale pink colour
• Electrochemical cells also are an example of a redox reaction as the electron transfer between products creates a flow of electrons which therefore creates an electrical current
• Electrochemical cells consist of:

  • two solutions
  • two metal electrodes
  • salt bridge
• A salt bridge is used to close the system and allows for ions to flow. It's paper soaked in KNO3
• Positive cell potentials means the substances are more easily reduced and will gain electrons and vice versa
• Standard hydrogen electrode:

  
• Ecell = E right - E left
• The more positive the Ecell value the more favourable the reaction
• The limitations of the standard cell potential and SHE is that although the reaction is shown to be feasible it may not actually occur in practice
• Rusting is a redox reaction that occurs in the presence of water and oxygen to produce a hydrated metal oxide
• Rusting can be prevented by applying a coating of metal which acts as a sacrificial metal and a barrier between the metal and the oxygen and water
• A coordination number is the number of bonds formed between the metal ion and the ligands
• Octahedral ligands are formed with H2O and NH3 and have a bond angle of 90º and a coordination number of 6
• Square planar ligands form with platinum and nickel which has a 4 coordination number and a bond angle of 90º
• Transition metals are all metals that have similar physical properties like high melting points but have special chemical properties like:

  • form complexes
  • form coloured ions in solution
  • variable oxidation states
  • good catalysts
• A ligand is a molecule or ion that has a lone pair to form a dative covalent bond to the metal ion
• Ligand types:

  • monodentate = form one coordinate bond like H2O and Cl-
  • bidentate = form two coordinate bonds like NH2CH2CH2NH2
• Colour of ion complexes can change due to their coordination number, oxidation state and type of ligand bonded
• Colours arise in transition metals due to the absorbance and reflection of light as the ligands cause the d-orbital to split and some electrons will be promoted to higher energy levels. The change in energy between states corresponds to a specific wavelength and frequency. It reemits complementary colour
• In colourless iosn there are no electrons available to absorb light and are therefore not excited so no colour is seen
• Ligand substitution is when a ligand can be exchanged in a complex for another ligand
• Complexes with just Cl- ligands always have a coordination number of 4
• Fe2+:

  • green solution with metal-aqua ion
  • green ppt with OH- and NH3
  • No change with excess OH- and NH3
• Fe3+

  • yellow solution with metal-aqua ion
  • brown ppt with OH- and NH3
  • no change with excess OH- and NH3
• Cu2+

  • blue solution with metal-aqua ion
  • blue ppt with OH- and NH3
  • no change with excess OH- dark blue with excess NH3
• In some ligands OH- ions are used to donate electrons to the metal ion and remove the charge
• Colorimtery can be used to determine concentration of a coloured solution by using known concentration and plotting a graph, ensure complementary colour filter selected