Reactions of inorganic ions

in an aqueous solution, without presence of of other ions

have a central metal atom with 6 water ligands

• octahedral shape

• coordination number → 6

metal aqua ions often present in the crystals

e.g

• the pink colour in crystals of hydrated cobalt (II) chloride is due to the same ion [Co(H2O)6]

  2+ as is in

  solutions of cobalt (II) chloride.

blue

green

pale violet

BUT appear yellow/orange rather than pale violet as presence of small amounts of [Fe(H2O)5(OH) ] 2+ due to hydrolysis

colourless

loss of H+ from water ligands

O-H bond in water ligand breaks

replacement of water by other ligands

metal-ligand bond breaks

metal changes oxidation state

gain or loss of electrons

insoluble in water and form as precipitates.

they are known as metal(II) hydroxides or metal(III) hydroxides

Sometimes they are simply written as M(OH)2 or M(OH)3.

7

6

3

0

the more acidic the solution

To lose H+, the O-H bond in a water ligand must break

To break the electrons in the bond are pulled closer to the O

the higher the charge on the metal ion or the smaller the metal ion

• higher charge density

the stronger the pull on electrons away from the H and towards the O breaking the O-H bond

hydrolysis may take place but other reactions may also take place

• The base removes H+ pushing equilibria right

e.g ammonia, hydroxide ions and carbonate ions

insoluble neutral complex will form as a precipitate

excess base → may react further

[Fe(H2O)4(OH)2]

green ppt

• darkens on standing due to oxidation to [Fe(H2O)3(OH)3]

[Cu( H2O)4(OH)2]

blue ppt

[Fe(H2O)3(OH)3]

brown ppt

[Al(H2O)3(OH)3]

white ppt

[Al(H2O)2(OH)4]-

re-dissolves to give a colourless solution

no further reaction

[Fe(H2O)4(OH)2]

green ppt

• darkens on standing due to oxidation to [Fe(H2O)3(OH)3]

[Cu( H2O)4(OH)2]

blue ppt

[Fe(H2O)3(OH)3]

brown ppt

[Al(H2O)3(OH)3]

white ppt

no further reaction

[Cu(H2O)2(NH3)4]2+

DEEP blue solution

[Cu( H2O)4(OH)2] → [Cu(H2O)2(NH3)4]2+

[Al(H2O)3(OH)3]

White ppt

bubbles of CO2 gas

[Fe(H2O)3(OH)3]

brown ppt

bubbles of CO2 gas

FeCO3

green ppt

CuCO3

blue-green ppt

[FeCl4]2-

yellow solution

[CuCl4]2-

green solution

[FeCl4]-

yellow solution

[AlCl4]-

colourless solution

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

green sol → green ppt

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

blue sol → blue ppt

[Fe(H2O)6]3+ + 3OH- → [Fe(H2O)3(OH)3] + 3H2O

orange sol → brown ppt

[Al(H2O)6]3+ + 3OH- → [Al(H2O)3(OH)3] + 3H2O

colourless sol → white ppt

[Al(H2O)3(OH)3] + OH- → [Al(H2O)2(OH)4]- + H2O

nvc

[Fe(H2O)6]2++ 2NH3 ® [Fe(H2O)4(OH)2] + 2NH4+

green sol → green ppt

[Cu(H2O)6]2+ + 2NH3 → [Cu(H2O)4(OH)2] + 2NH4+

blue sol → blue ppt

[Cu(H2O)4(OH)2] + 4NH3 → [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH-

blue ppt → deep blue sol

[Fe(H2O)6]3+ + 3NH3 → [Fe(H2O)3(OH)3] + 3NH4+

orange sol → brown ppt

[Al(H2O)6]3+ + 3NH3 → [Al(H2O)3(OH)3] + 3NH4+

colourless sol → white ppt

[Fe(H2O)6]2++ CO32- → FeCO3 + 6H2O

Green sol → green ppt

[Cu(H2O)6]2++ CO32- → CuCO3 + 6H2O

ble sol → blue/green ppt

2[Fe(H2O)6]3++ 3CO32- → 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2

orange sol → brown ppt + bubbles

2[Al(H2O)6]3+ + 3CO32- → 2[Al(H2O)3(OH)3] + 3H2O + 3CO2

colourless sol → white ppt and bubbles

[Fe(H2O)4(OH)2] + 2H+ → [Fe(H2O)6]2+

green ppt → green sol

[Cu(H2O)4(OH)2] + 2H+ → [Cu(H2O)6]2+

blue ppt → blue sol

[Fe(H2O)3(OH)3] + 3H+ → [Fe(H2O)6]3+

brown ppt → violet sol

[Al(H2O)3(OH)3] + 3H+ → [Al(H2O)6]3+

white ppt → colourless sol

[Al(H2O)3(OH)3] + OH- → [Al(H2O)2(OH)4]

white ppt → colourless sol

amphoteric

[Fe(H2O)4(OH)2]

[Cu(H2O)4(OH)2]

[Fe(H2O)3(OH)3]

[Al(H2O)3(OH)3]

[Fe(H2O)6]2+ + 4Cl– → [FeCl4]2– + 6H2O

green sol → yellow sol

[Cu(H2O)6]2+ + 4Cl– → [CuCl4]2– + 6H2O

blue sol → yellow sol

[Fe(H2O)6]3+ + 4Cl– → [FeCl4]– + 6H2O

orange sol → yellow sol

[Al(H2O)6]3+ + 4Cl– → [AlCl4]– + 6H2O

colourless sol → colourless sol