Transition Metals 2

• What can transition metal ions be identified by?

  Their colour
• How does colour arise in transition metal ions?

  By absorbing some wavelengths of visible light
• What do we see when light is transmitted through a coloured ion?

  The complementary colour to the absorbed light
• What colour does copper sulfate appear when it absorbs red light?

  Cyan (pale blue)
• What happens to an electron when light of the right frequency is absorbed?

  It moves from the ground state to an excited state
• What is the term for the transition of an electron from ground to excited state?

  d→d electron transition
• What does the equation ∆E = hν = hc/λ represent?

  The energy difference between electron states
• What is the visible region of the spectrum's wavelength range?

  400nm to 800nm
• What happens to the 3d orbitals of a transition metal in an octahedral complex?

  They split into two energy groups

  
• What causes the colour of transition metal complex ions?

  Absorption of light that excites d electrons
• What factors affect the size of ΔE for d→d transitions?

  The ligand, coordination number, and oxidation state
• What do strong-field ligands do to ΔE?

  Induce a large ΔE
• Which ligands are considered strong-field ligands?

  CN- and CO
• What do weak-field ligands do to ΔE?

  Induce a small ΔE
• What colour change occurs when ligands change in a transition metal ion?

  It often causes a colour change
• What is the oxidation state of [Fe(H2O)6]2+?

  Green
• Why is [Fe(H2O)6]3+ usually seen as yellow?

  Due to the presence of [Fe(H2O)5OH]2+
• What is a colorimeter used for?

  Testing the concentration of a solution
• How is a calibration graph created using a colorimeter?

  By recording absorbance of known concentrations

  
• Why is colorimetry preferred over titration?

  It is quicker and uses smaller volumes
• What does the Beer-Lambert Law state about the calibration graph?

  It should be a straight line
• Why is the choice of filter important in colorimetry?

  It must match the absorbed wavelength
• How does path length affect light absorption in colorimetry?

  Longer path increases light absorption
• What is a cuvette used for in colorimetry?

  To maintain a constant path length
• How can colorimetry determine the concentration of KMnO4?

  By comparing absorbance to a calibration curve
• What does a spectrophotometer measure?

  The radiation passing through the solution
• How does a spectrophotometer differ from a colorimeter?

  It uses visible or ultraviolet radiation
• What is done if a solution is too dilute for a spectrophotometer?

  Add a suitable ligand for a more intense colour
• What oxidation state is commonly occurring for transition metals?

  +2

  
• Why do transition metals show variable oxidation states?

  Due to unfilled d-subshells at the same energy level
• What colour is VO2+ in oxidation state +5?

  Yellow
• What does metallic zinc do in redox reactions?

  Acts as a good reducing agent
• What is observed when vanadium exists in different oxidation states?

  Two different colours of solution
• What are the half equations for the reduction reactions of vanadium (V)?

  • +5 to +4: VO2+ + 2H+ + e- ⇌ VO2+ + H2O
  • +4 to +3: VO2+ + 2H+ + e- ⇌ V3+ + H2O
  • +3 to +2: V3+ + e- ⇌ V2+
• How is the ionic equation for redox reactions determined?

  By combining oxidation and reduction half equations
• How does pH affect redox reactions of transition metal ions?

  It influences the redox potential
• What happens to MnO4- ions in acidic solution?

  They are reduced to Mn2+ ions
• What happens to MnO4- ions in alkaline solution?

  They are reduced to MnO42- ions
• What is Tollen’s reagent used for?

  To test for the presence of an aldehyde
• What happens when Tollen’s reagent is warmed with an aldehyde?

  Silver ions are reduced to silver metal