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Module 5 Chapter 24 (24.1 d-block elements (Catalysts (Catalyst- substance…

- - - - Chromium- 24 electrons- 3d5 4s1
      - Copper- 29 electrons- 3d10 4s1
      - Due to stability- half full d sub-shell and fully filled d sub-shell give additional stability to atoms of chromium and copper
    - - 4s orbital fills before 3d
      - When forming ions 4s empties before 3d
  - - - Form compounds in which the transition metal has different oxidation states
      - Form coloured compounds
      - Elements and compounds can act as catalysts
  - - - Fe2+ = Pale green
      - Fe3+ = yellow
    - - Cr(III)- green
      - Cr(VI) - yellow or orange
- - - - Can donate one pair of electrons to central metal ion
      - e.g. Water (neutral) , ammonia (neutral), Chloride (-1), cyanide CN (-1) and hydroxide (-1)
    - - Can donate two pairs of electrons to central metal ion
      - e.g.
        
        1,2 Diaminoethane (en) (Neutral) - each nitrogen donates a pair of electrons
        
        Ethanedioate ion (-2)- each oxygen atom donates pair
  - - - Octahedral shape
      - Bond angle of 90°
    - - Tetrahedral
        
        Bond angle 109.5°
        
        More common
      - Square Planar
        
        Bond angle 90°
        
        Only occurs when central metal ion is- Platinum (II), Palladium (II) or Gold (III)
- - - - Same structural formula but different arrangement of atoms in space
      - Two types in complex ions
        
        1) Cis-trans (4 and 6 coordination)
        
        2) Optical (Only 6 coordination)
    - - Square Planar
        
        Cis
        
        Identical groups 90° apart
        
        Trans
        
        Identical groups 180° apart
      - Octahedral
        
        Mododentate
        
        Cis
        
        Identical groups 90° apart
        
        Trans
        
        Identical groups 180° apart
        
        Bidentate
        
        Cis
        
        Identical groups 90° apart
        
        Trans
        
        Identical groups 180° apart
    - - Only in octahedral with bidentate ligands
      - Called enantiomers- non-superimposable mirror images of each other
      - Example
- - - - Oxidation
        
        Redox titration where Fe2+ reduced to Fe3+ and MnO4 - oxidised to Mn2+
        
        From purple to colourless
        
        MnO4 - + 8H+ +5Fe2+ -> Mn2+ +5Fe3+ + 4H2O
      - Reduction
        
        Fe3+ reduced to Fe2+ and I- oxidised to I2
        
        Fe3+ Orange-brown to Fe 2+ pale green I2 is brown so change hard to see
        
        2Fe3+ + I- -> 2Fe2+ + I2
    - - Reduction
        
        Add zinc, Cr2O7 2- reduced to Cr3+
        
        Cr2O7 2- + 14H+ + 3Zn(s) -> 2Cr3+ + 7H2O + 3Zn2+ Orange to green
        
        Excess Zn reduced further Zn + 2Cr3+ -> Zn 2+ + 2Cr2+ Green-> Pale Blue
      - Oxidation
        
        Add H2O2, Cr3+ oxidised to Cr2O7 2-
        
        3H2O2 + 2Cr3+ + 10OH- -> 2CrO4 2- + 8H2O
    - - Disproportionation
        
        Cu2O (s) (+1) + H2SO4 (aq) -> Cu(s) (0) + CuSO4 (+2) + H2O
        
        Copper both oxidised and reduced
      - Reduction
        
        Add excess iodide ions Cu2+ reduced to Cu+ and I- oxidised to I2
        
        2Cu2+ (pale blue) + 4I- -> 2CuI (white ppt) +I2 (s)(brown)
- - - - Excess- Cu(H2O)6]2+ + 4NH3(aq) -> [Cu(NH3)4(H2O)2]2+ + 4H2O (l) DARK BLUE
      - Dropwise- Cu(OH)2 - Pale blue precipitate forms- OH- from NH3 reacting with water to form NH4OH
  - - - [Cu(H2O)6]2+ + 4Cl- -> [Cu(Cl)4] + 6H2O
      - Chlorine comes from Conc. HCl
      - YELLOW SOLUTION
  - - - Excess- [Cr(H2O)6]3+ + 6NH3 (aq) -> [Cr(NH3)6]3+ + 6H20 PURPLE
      - Dropwise- Cr(OH)3 forms Grey-green precipitate
  - - - Cu2+
        
        Blue solution
        
        Blue precipitate (Cu(OH)2)
      - Fe2+
        
        Pale green solution
        
        Green precipitate (Fe(OH)2)
        
        Same reaction with ammonia
      - Fe3+
        
        Pale yellow
        
        Orange-brown precipitate (Fe(OH)3)
        
        Same reaction with ammonia
      - Mn2+
        
        Pale pink solution
        
        Light brown precipitate (Mn(OH)2)
        
        Same reaction with ammonia
      - Cr3+
        
        Violet solution
        
        Grey-green precipitate (Cr(OH)3)
        
        Soluble in NaOH forms dark green solution
    - - Fe2+ central metal ion with 4 nitrogen
      - Binds to 2 oxygen in lungs (coordination no. 6)
      - Body- O2 replaced with H2O
      - If CO enters will bond instead of O2 (irreversible) -can lead to death if CO conc. high