Transition Metals

• what are transition metals?

  a transition element is a d-block element that is able to form stable ions with a partially filled (incomplete) d-subshell
• why do different complexes have different coloure?

  • in different complexes, d-orbital splitting will be different
  • the energy absorbed is used to excite electrons
  • different wavelengths of light will be reflected
• what is the chelate effect?

  an increase in entropy
• [Co(H2O)6]2+ is oxidised to [Co(H2O)6]3+, with H2O2 being the oxidising agent, and it loses an electron
• coordination number of [CoCl4]2- is different than that of CoCl2 because Cl- ligand is too big to fit more than 4 around Co2+
• what is a complex ion?

  it has ligands linked by coordinate bonds
• in terms of electrons, explain why an aqueous solution of CoSO4 has a red colour?

  • light is absorbed due to electrons getting excited
  • red light remains and is reflected
• role of haemoglobin?

  transporting oxygen around the body
• why is carbon monoxide poisoning harmful?

  CO bonds to the Fe in haemoglobin and displaces oxygen
• what does each term mean in the equation: ΔE = hv?

  • ΔE= the energy absorbed
  • h= Plank’s constant
• three factors that may cause the frequency of light absorbed to change when a complex ion reacts?

  • change of ligand
  • change in coordination number
  • change in oxidation number
• why might well-water be more beneficial to health than pure water?

  because the Fe it contains is needed for haemoglobin
• explain why electron transition can cause a solution containing a transition metal ion to appear coloured?

  • light is absorbed
  • the remaining wavelength is transmitted
• MnO4^-?

  purple
• what is a feature of transition metals

  that allows them to be good catalysts?

  variable oxidation states
• how can the poisoning of catalysts be reduced in industrial processes?

  by purifying the reactants / removing impurities
• how can you tell that a transition metal has variable oxidation states through observing a reaction?

  • because different colours of solution will be observed
  • each colour corresponds to the metal in each of its oxidation states
• what is a complex?

  a central metal ion surrounded by ligands
• ligand substitution is incomplete for copper when NH3 is in excess, and forms a deep blue solution
• energy change (ΔH ) for ligand substitution reactions is very small as the bonds being made are similar to the bonds being broken, therefore ΔH is close to 0
• what transition metals can form square planar complex?

  Platinum and Nickel
• what is the ratio of MnO4- ions to C2O4^2- ions?

  2 : 5
• what is the ratio of MnO4- ions to Fe^2+ ions?

  1 : 5
• what is the ratio of C2O4^2- ions to Fe^2+ ions?

  1 : 2
• transition metals transfer electrons to produce a reactive intermediate and speed up the reaction rate
• Contact Process

  1. V2O5 + SO2 —-—> V2O4 + SO3
  2. 2V2SO4 + O2 ———-> 2V2O5
• heterogenous catalysts can be poisoned by impurities that block the active sites and prevent adsorption
• Homogenous catalyst

  1. S2O8^2- + 2Fe^2+ ———> 2Fe^3+ 2SO4^2-
  2. 2Fe^3+ + 2I^ ——> 2Fe^2+ + I2
• In autocatalysis reactions, as the product is formed overtime, the rate of reaction also increases
• the reaction between MnO4- and C2O4^2- ions in acidic conditions is an example of autocatalysis

  1. reduce MnO4^- to Mn2+ ions and balance equations
  2. reduce C2O4^2- to CO2 and balance
  3. combine the two equations
• [Cu(H2O)] 2+ reacts with ammonia in two stages

  1. complex + 2NH3 ——> [Cu(H2O)4(OH)2]2+ + 2NH4+
  2. [Cu(H2O)4(OH)2]2+ + 4NH3 —-> [Cu(NH3)4(H2O)2]2+ + 2OH- + 2H2O
• dichromate ion oxidises to Cr3+
• why might a calculated ratio of two ions be different from the expected value?

  incomplete oxidation may have occurred in the preparation
• how does a drying agent work?

  water vapour is absorbed by the drying agent
• what is an autocatalyst?

  when the catalyst is a reaction product
• what does heterogenous mean?

  when the catalyst is in a different phase from the reactants
• autocatalysis involving Mn2+ as a catalyst

  • 4Mn^2+ + MnO4- —-> 5Mn^3+ + 4H2O
  • 2Mn^3+ + C2O4- —> 2Mn^2+ + 2CO2
• why do different complexes have different colours?

  • d-orbital splitting will be different
  • energy is absorbed causing an electron to be excited
  • different wavelengths of light will be reflected
• oxidising agents get reduced in equations, for example H2O2 oxidising Co2+ ions to Co3+ ions;


  2Co2+ + H2O2 ——> 2Co3+ + 2OH-
• how does Fe act as a heterogenous catalyst?

  • nitrogen and hydrogen adsorb onto the surface of the Fe
  • bonds will weaken
  • the products will desorb