Transition metals

• Why is CO toxic to humans?

  form strong coordinate bond with haemoglobin, stronger bond than made with oxygen so it prevents oxygen attaching to haemoglobin. CO stability is greater than CO2
• Is Zn a transition metal

  No, only forms 2+ ion
• Is Sc a transition metal?


  No, only forms 3+ ion
• Are all D block elements transition metals?

  No, only elements from Ti to Cu
• FOUR properties of transition metals

  1. All have coloured ions

  2. Have variable oxidation states (but not all are stable)

  3. The form complexes

  4. Show catalytic activity
• Which two metals are not transition metals? And why?

  Sc 3+ because it has an empty 'd' subshell, and ZN 2+ because its 'd' subshell is completely filled
• What is a ligand?

  A molecule or ion with a lone pair that forms a dative covalent bond to a transition metal
• What is a complex?

  Metal ion with ligands datively bonded to it. Complexes can be any charge - i.e positive, negative or neutral
• Monodentate

  Form one dative bond e.g NH3, H2O, Cl-, CN-, OH-
• State the shape, bond angle and common occurrence for:

  Co-ordination number 2

  Linear

  180 degree

  Ag+ complexes e.g. [Ag(NH3)2]+ (Tollen's Reagent)
• State the shape, bond angle and common occurrence for:

  Co-ordination number 4 (normal)

  Tetrahedral

  109.5 degrees

  Large ligands (i.e Cl-) e.g. [CuCl4]2-
• State the shape, bond angle and common occurrence for:

  Co-ordination number 4 (weird)

  Square planar

  90 degrees

  Pt2+ complexes e.g. [PtCl4]2-
• State the shape, bond angle and common occurrence for:

  Co-ordination number 6

  Octahedral

  90 degrees

  Most common (i.e aqua ions) e.g. [Cu(H2O)6]2+
• Which 2 shapes can have cis-trans isomerism?

  Octahedral

  Square planar

  Both must not contain all the same ligands
• Which shape can have optical isomerism?

  The cis isomer of an octahedral
• What shape are metal aqua ions?

  Octahedral - hexa aqua ions
• Colour of [Cu(H2O)6]2+

  Blue
• Colour of [Fe(H2O)6]2+

  Green
• Colour of [Fe(H2O)6]3+

  Pale yellow/brown
• Colour of [Mn(H2O)6]2+

  Pale pink
• Colour of [Cr(H2O)6]3+

  Violet
• Adding NaOH or a small amount of NH3 to:

  [Cu(H2O)6]2+

  And the equations:

  Blue precipitate

  [Cu(H2O)6]2+ + 2OH- --> [Cu(H2O)4(OH)2] (s) + 2H2O

  Cu2+ + 2OH- --> Cu(OH)2 (s) (If you add acid, it reverses this reaction)

  [Cu(H2O)6]2+ + 2NH3 --> [Cu(H2O)4(OH)2] (s) + 2NH4+
• Adding NaOH or a small amount of NH3 to:

  [Fe(H2O)6]2+

  And the equations:

  Green precipitate

  [Fe(H2O)6]2+ + 2OH- --> [Fe(H2O)4(OH)2] (s) + 2H2O

  Fe2+ + 2OH- --> Fe(OH)2 (s) (If you add acid, it reverses this reaction)

  [Fe(H2O)6]2+ + 2NH3 --> [Fe(H2O)4(OH)2] (s) + 2NH4+
• Adding NaOH or a small amount of NH3 to:

  [Fe(H2O)6]3+

  And the equations:

  Brown precipitate

  [Fe(H2O)6]3+ + 3OH- --> [Fe(H2O)3(OH)3] (s) + 3H2O

  [Fe(H2O)6]3+ + 3NH3 --> [Fe(H2O)3(OH)3] (s) + 3NH4+
• Adding NaOH or a small amount of NH3 to:

  [Mn(H2O)6]2+

  And the equations:

  Cream/Light brown precipitate

  [Mn(H2O)6]2+ + 2OH- --> [Mn(H2O)4(OH)2] (s) + 2H2O

  Mn2+ + 2OH- --> Mn(OH)2 (s) (If you add acid, it reverses this reaction)

  [Mn(H2O)6]2+ + 2NH3 --> [Mn(H2O)4(OH)2] (s) + 2NH4+
• Adding NaOH or a small amount of NH3 to:

  [Cr(H2O)6]3+

  And the equations:

  Green precipitate

  [Cr(H2O)6]3+ + 3OH- --> [Cr(H2O)3(OH)3] (s) + 3H2O

  [Cr(H2O)6]3+ + 3NH3 --> [Cr(H2O)3(OH)3] (s) + 3NH4+
• What is special about the [Cr(H2O)3(OH)3] (s) precipitate and why?

  It is amphoteric because Cr has a high charge density
• Define amphoteric?

  An amphoteric species can react with either a base or an acid
• What type of reaction is adding excess NH3?


  Ligand exchange reaction
• What is the Stability Constant and what can it be used for?

  Kstab = equilibrium constant for the overall reaction

  Enables to predict which complex will be formed
• What type of reaction is where some of the reactants change oxidation state?


  Redox reactions
• In which type of solution does oxidation of transition metals most easily occur and why?

  Alkaline solution

  Negative ions tend to form in alkaline solutions and it is easier to lose elections in alkaline solution to form a negatively charged species
• In which type of solution does reduction of transition metals most easily occur?

  Acid solution
• What reagent is used to reduce [Cr(OH)6]3- to CrO4 2-?

  What is the colour change?

  And the equation:

  H2O2 (oxidising agent)

  Green solution (+3) to Yellow solution (+6)

  3 H2O2 + 2 [Cr(OH)6]3- --> 2 (CrO4)2- + 8 H2O + 2 OH-
• Redox Reaction with Cu2+ is which type of reaction?

  Which is the reagent used?

  What is the colour change / visible change?

  And the equation:

  Disproportionation

  I-

  Pale blue solution to brown solution and a white precipitate

  2Cu2+ + 4I- --> 2CuI + I2
• What colour are I- ions?

  Colourless
• What reagent is used to convert CrO4 - to (Cr2O7)2-?

  What are the colour changes?

  What type of reaction is this?

  Adding acid e.g H2SO4

  Yellow solution to Orange solution

  Acid-base, NOT redox. Just a reaction where one chromate (VI) joins with another to form DIchrimate (VI). No change in oxidation states
• The ionic equation to convert CrO4- to (Cr2O7)2-

  CrO4 - + 2H+ <---> (Cr2O7)2- + H2O (equilibrium)
• What would you add to go the other way i.e (Cr2O7)2- to CrO4-?

  Alkali / Base
• What reagent is used to reduce the dichromate ion (VI) to Cr3+ and then eventually Cr2+?

  What are the colour changes?

  Add Zn in acid solution of dichromate ions (acidified dichromate)

  Orange solution to green solution, then eventually to blue solution.