5.3.1. Transition Elements

• [Cu(H2O)6]2+ Cu2+ (aq)

  BLUE SOLUTION
• [Cu(OH)2(H2O)4] Cu(OH)2

  BLUE PPT
• [Cu(NH3)4(H2O)2]2+

  DEEP BLUE SOLUTION
• [CuCl4]2-

  YELLOW SOLUTION
• Cu2+ (aq) + HCl (aq) can look green as reaction is reversible. Blue and yellow makes green
• [Fe(H2O)6]2+ Fe2+ (aq)

  PALE GREEN SOLUTION
• [Fe(OH)2(H2O)4] Fe(OH)2

  GREEN PPT

  if left in air, ppt will start to turn brown as Fe2+ oxidises to Fe3+
• [Fe(H2O)6]3+ Fe3+ (aq)

  YELLOW SOLUTION
• [Fe(OH)3(H2O)3] Fe(OH)3

  ORANGE/BROWN PPT
• [Cr(H2O)6]3+ Cr3+ (aq)

  VIOLET SOLUTION when pure

  impurities cause it to appear green
• [Cr(OH)3(H2O)3] Cr(OH)3

  GREY/GREEN PPT

  excess OH- and ppt dissolves into green solution, [Cr(OH)6]3-
• [Cr(OH)6]3-

  GREEN SOLUTION
• [Cr(NH3)6]3+

  PURPLE SOLUTION
• [CrO4]2- (aq)

  YELLOW
• [Cr2O7]2- (aq)

  ORANGE
• [Mn(H2O)6]2+ Mn2+ (aq)

  VERY PALE PINK SOLUTION / COLOURLESS
• [Mn(OH)2(H2O)4] Mn(OH)2

  BEIGE / LIGHT BROWN
• [MnO4]2-

  PURPLE
• Electron configuration in Chromium (24) is [Ar] 4s1 3d5
• Electron configuration in Copper (29) is [Ar] 4s1 3d10
• In chromium and copper, the 3d subshell takes one electron from the 4s subshell
• 4s subshell is filled before 3d, and 4s is lost before 3d
• Transition elements have at least one ion with an incomplete d sub-shell

  Sc only forms Sc3+, which has no 3d electrons

  Zn only forms Zn2+, which has a complete d subshell
• Transition elements can show more than one oxidation state in compounds (variable oxidation state)
• Transition elements can act as catalysts
• Heterogenous catalysts = catalyst and reactants in different physical state
• Contact process catalyst is V2O5 (heterogenous)
• Haber process catalyst is Fe (heterogenous)
• Hydrogenation of alkenes catalyst is Ni (heterogenous)
• Decomposition of hydrogen peroxide catalyst is MnO2 (heterogenous)
• Homogenous catalysts = catalyst and reactants in same physical state