Aqueous ions

• Cu(H2O)4(OH)2 with conc. NH3

  deep blue solution ( ligand substitution) Cu(NH3)6

  
  

  
  

  [ Cu(H20)2(NH3)4 ] 2+
• [Cu(H2O)6]2+ with Conc. HCl

  yellow - green solution ( ligand substitution)
• [Fe(H2O)6]3+ with conc. HCl

  yellow solution (ligand substitution)
• [Fe(H2O)6]2+(aq) with conc. HCl

  yellow solution (ligand substitution)
• excess NaOH to Fe(H2O)4 (OH)2 (s)

  no further change
• excess NH3 to Fe(H2O)4 (OH)2 (s)

  no further chnage
• excess NaOH to Cu(H2O)4 (OH)2 (s)

  no further change
• excess NaOH to Fe(H2O)3 (OH)3 (s)

  no further change
• excess NH3 to Fe(H2O)3 (OH)3 (s)

  no further change
• excess NH3 to Al(H2O)3 (OH)3 (s)

  no further change
• What does the acidity of an aqua-ion solution depend on?

  • CHARGE / SIZE RATIO (charge density)
  • Smaller charge / size ratio
  • less polarisation of the O-H bond in co-ord bonded water so less chance of it breaking so less dissociation so less H+ formation
• why are [m(H2O)6]3= more acidic than [m(H2O)6]2+ more acidic than 2+


  • M3+ ions have a higher charge density than M2+ ions​
  • Polarise water molecules more
  • This causes the O—H bond in the Water ligands to weaken and break
  • releasing H+(aq) ions
• solutions containing 3+ hexaaqua ions usually have a pH values:

  1 to 3
• solutions containing 2+ hexaaqua ions typivally have pH value

  5 - 6
• What does a former 3+ ions PPT act as when added to acid?

  A Brønsted-Lowery base accepts some protons
• How does the hydrolysis of metal-aqua ions using NH3 Work?

  NH3 accepts protons in water - this makes OH-
• what happens when you add conc. HCL to [Cu(H2O)6]2+?

  [Cu(H2O)6]2+ + 4Cl- => [CuCl4]2- + ^H2)Yellow-Green solutionLigand substitution
• addition od XS OH- to Fe(H2O)4(OH)2


  still Fe(H2O)4(OH)2green precipitateno visible change
• additon of XS NH3 or conc. NH3 to Fe(H2O)4(OH)2

  Fe(H2O)4(OH)2

  still green precipitate

  no visible change
• addition of XS OH- to Fe(H2O)3(OH)3

  stil Fe(H2O)3(OH)3 brown precipitate no visible change
• addrtion of XS OH- to Al(H2O)3(OH)3

  Al(H2O)3(OH)3 + 3OH- => [Al(OH)6]3- + 3H2O colourless solution AMPHOTERIC(Test for Al3+ ions)
• addition of XS Nh3 or conc. NH3 to [Al(H20)6]3+

  still Al(H2O)3(OH)3

  White precipitate

  no visible change
• Are 2+ ions or 3+ ions more acidic in solution? why

  • 3+ ions are much more acidic
  • 3+ ions are smaller and more highly charged, so have a higher charge density.
  • They attract the electrons from the oxygen of the ligands much more strongly. This weakens the O-H bonds
  • so the complex readily releases a H+ ion into the solution, making it acidic
• [Fe(H20)5(OH)]2+ (aq) complex ion acting as

  Bronsted-Lowry - donates a proton
• Define a Lewis acid

  Electron pair acceptor
• Define a Lewis base

  Electron pair donor
• What is acting as the Lewis acid and what is acting as the Lewis base during the formation of complex ions?

  The metal ion is acting at the Lewis acid and the ligands as Lewis bases
• V (V)? [VO2(H20)4]+

  yellow
• V (IV)?

  [VO2(H20)5]2+ blue
• V (III)

  green

  [VO2(H20)6]3+
• V (II)?

  Purple

  [V(H20)6]2+
• Fe2+ reactions:

  A) green soloution

  B) green precipitate

  C) goes brown on standing in air

  D) green precipitate

  E) goes brown on standing in air

  F) green precipitate

  
• Why does the green ppt go brown on standing in air in the reaction of Fe2+ with NH3 ?

  Oxygen in the air oxidises Fe2+ to Fe3+, and [Fe(OH)3 (H2O)3 ] is brown, so colour changes
• reactions of Fe3+

  A) purple soloution

  B) brown precipitate

  C) brown precipitate

  D) effervescence

  
• reactions of Al3+

  A) Colourless solution

  B) white precipitate

  C) Colourless solution

  D) white precipitate

  E) white precipitate

  F) effervescence

  
• Give an equation to show how the complex ion Z can act as a Bronsted-Lowry acid with water.

  [Al(H2O6]3+ + H20 —-> [Al(H2O)5(OH)]2+ + H3O+
• Reagent for reaction 3

  Excess Zn

  
• Explain why an aqueous solution containing [Fe(H20)6]3+ ions has a lower pH than an aqueous solution containing (Fe(H20)6)2+ ions.

  • Fe3+ is smaller (than Fe2+)
  • Fe3+ has a greater charge density
  • Fe3+ ions are more polarising
  • So more O-H bonds in the water ligands break
  • more H+ ions released
• [Fe(H2O)6]2+ + CO3. 2- = FeCO3 +6H20

  Is a light green precipitate
• Colour of CuCO3

  green - blue precipitate