metal aqua 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
salts crystallised from solution
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.
complex: [Cu(H2O)6] 2+ - colour ?
blue
complex: [Fe(H2O)6] 2+ - colour ?
green
complex: [Fe(H2O)6] 3+ - colour ?
pale violet
BUT appear yellow/orange rather than pale violet as presence of small amounts of [Fe(H2O)5(OH) ] 2+ due to hydrolysis
complex: [Al(H2O)6] 3+ - colour ?
colourless
hydrolysis in reactions of metal aqua ions
loss of H+ from water ligands
O-H bond in water ligand breaks
substitution in reactions of metal aqua ions
replacement of water by other ligands
metal-ligand bond breaks
redox in reactions of metal aqua ions
metal changes oxidation state
gain or loss of electrons
neutral complex ions
e,g. M(H2O)4(OH)2 or M(H2O)3(OH)3
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.
aqua ion: [M(H2O)6]+ - pH ?
7
aqua ion: [M(H2O)6]2+ - pH ?
6
aqua ion: [M(H2O)6]3+ - pH ?
3
aqua ion: [M(H2O)6]4+ - pH ?
0
the higher the charge on the metal ion ….
the more acidic the solution
the higher the charge on the metal ion the more acidic the solution -
WHY ?
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
reaction with bases
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)6]2+ add NaOH dropwise
ppt
colour
[Fe(H2O)4(OH)2]
green ppt
darkens on standing due to oxidation to [Fe(H2O)3(OH)3]
[Cu(H2O)6]2+ add NaOH dropwise
ppt
colour
[Cu( H2O)4(OH)2]
blue ppt
[Fe(H2O)6]3+ add NaOH dropwise
ppt
colour
[Fe(H2O)3(OH)3]
brown ppt
[Al(H2O)6]3+ add NaOH dropwise
ppt
colour
[Al(H2O)3(OH)3]
white ppt
[Al(H2O)6]3+ add NaOH dropwise then add in excess NaOH
ppt
colour
[Al(H2O)2(OH)4]-
re-dissolves to give a colourless solution
[Fe(H2O)6]3+, [Cu(H2O)6]2+ ,[Fe(H2O)6]2+
add NaOH dropwise then add in excess NaOH
ppt
colour
no further reaction
[Fe(H2O)6]2+ + add NH3 drop wise
ppt
colour
[Fe(H2O)4(OH)2]
green ppt
darkens on standing due to oxidation to [Fe(H2O)3(OH)3]
[Cu( H2O)6]2+ + add NH3 drop wise
ppt
colour
[Cu( H2O)4(OH)2]
blue ppt
[Fe( H2O)6]3+ + add NH3 drop wise
ppt
colour
[Fe(H2O)3(OH)3]
brown ppt
[Al( H2O)6]3+ + add NH3 drop wise
ppt
colour
[Al(H2O)3(OH)3]
white ppt
[Fe(H2O)6]3+, [Al(H2O)6]3+ ,[Fe(H2O)6]2+
add NH3 dropwise then add in excess NH3
ppt
colour
no further reaction
[Cu( H2O)6]2+ + add NH3 drop wise then in excess NH3
ppt
colour
[Cu(H2O)2(NH3)4]2+
DEEP blue solution
[Cu( H2O)4(OH)2] → [Cu(H2O)2(NH3)4]2+
[Al( H2O)6]3+ + add NaCO3 (aq)
ppt
colour
[Al(H2O)3(OH)3]
White ppt
bubbles of CO2 gas
[Fe( H2O)6]3+ + add NaCO3 (aq)
ppt
colour
[Fe(H2O)3(OH)3]
brown ppt
bubbles of CO2 gas
[Fe( H2O)6]2+ + add NaCO3 (aq)
ppt
colour
FeCO3
green ppt
[Cu( H2O)6]2+ + add NaCO3 (aq)
ppt
colour
CuCO3
blue-green ppt
[Fe( H2O)6]2+ + add conc HCl
ppt
colour
[FeCl4]2-
yellow solution
[Cu( H2O)6]2+ + add conc HCl
ppt
colour
[CuCl4]2-
green solution
[Fe( H2O)6]3+ + add conc HCl
ppt
colour
[FeCl4]-
yellow solution
[Fe( H2O)6]3+ + add conc HCl
ppt
colour
[AlCl4]-
colourless solution
equation of Fe(H2O)6 2+ add OH-
[Fe(H2O)6]2+ + 2OH- → [Fe(H2O)4(OH)2] + 2H2O
green sol → green ppt
equation of Cu(H2O)6 2+ add OH-
[Cu(H2O)6]2+ + 2OH- → [Cu(H2O)4(OH)2] + 2H2O
blue sol → blue ppt
equation of Fe(H2O)6 3+ add OH-
[Fe(H2O)6]3+ + 3OH- → [Fe(H2O)3(OH)3] + 3H2O
orange sol → brown ppt
equation of Al(H2O)6 3+ add OH-
[Al(H2O)6]3+ + 3OH- → [Al(H2O)3(OH)3] + 3H2O
colourless sol → white ppt
equation of Al(H2O)6 3+ add XS OH-
[Al(H2O)3(OH)3] + OH- → [Al(H2O)2(OH)4]- + H2O
nvc
equation of Fe(H2O)6 2+ add NH3
[Fe(H2O)6]2++ 2NH3 ® [Fe(H2O)4(OH)2] + 2NH4+
green sol → green ppt
equation of Cu(H2O)6 2+ add NH3
[Cu(H2O)6]2+ + 2NH3 → [Cu(H2O)4(OH)2] + 2NH4+
blue sol → blue ppt
equation of Cu(H2O)6 2+ add XS NH3
[Cu(H2O)4(OH)2] + 4NH3 → [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH-
blue ppt → deep blue sol
equation of Fe(H2O)6 3+ add NH3
[Fe(H2O)6]3+ + 3NH3 → [Fe(H2O)3(OH)3] + 3NH4+
orange sol → brown ppt
equation of Al(H2O)6 3+ add NH3
[Al(H2O)6]3+ + 3NH3 → [Al(H2O)3(OH)3] + 3NH4+
colourless sol → white ppt
equation of Fe(H2O)6 2+ add CO32- (NaCO3)
[Fe(H2O)6]2++ CO32- → FeCO3 + 6H2O
Green sol → green ppt
equation of Cu(H2O)6 2+ add CO32- (NaCO3)
[Cu(H2O)6]2++ CO32- → CuCO3 + 6H2O
ble sol → blue/green ppt
equation of Fe(H2O)6 3+ add CO32- (NaCO3)
2[Fe(H2O)6]3++ 3CO32- → 2[Fe(H2O)3(OH)3] + 3H2O + 3CO2
orange sol → brown ppt + bubbles
equation of Al(H2O)6 3+ add CO32- (NaCO3)
2[Al(H2O)6]3+ + 3CO32- → 2[Al(H2O)3(OH)3] + 3H2O + 3CO2
colourless sol → white ppt and bubbles
equation of [Fe(H2O)4(OH)2] add XS acid
[Fe(H2O)4(OH)2] + 2H+ → [Fe(H2O)6]2+
green ppt → green sol
equation of [Cu(H2O)4(OH)2] add XS acid
[Cu(H2O)4(OH)2] + 2H+ → [Cu(H2O)6]2+
blue ppt → blue sol
equation of [Fe(H2O)3(OH)3] add XS acid
[Fe(H2O)3(OH)3] + 3H+ → [Fe(H2O)6]3+
brown ppt → violet sol
equation of [Al(H2O)3(OH)3] add XS acid
[Al(H2O)3(OH)3] + 3H+ → [Al(H2O)6]3+
white ppt → colourless sol
equation of [Al(H2O)3(OH)3] add XS alkali
[Al(H2O)3(OH)3] + OH- → [Al(H2O)2(OH)4]
white ppt → colourless sol
[Al(H2O)3(OH)3] reacts with XS acid and alkali
amphoteric
metal hydroxides
[Fe(H2O)4(OH)2]
[Cu(H2O)4(OH)2]
[Fe(H2O)3(OH)3]
[Al(H2O)3(OH)3]
equation of [Fe(H2O)6]2+ add excess Cl–
[Fe(H2O)6]2+ + 4Cl– → [FeCl4]2– + 6H2O
green sol → yellow sol
equation of [Cu(H2O)6]2+ add excess Cl–
[Cu(H2O)6]2+ + 4Cl– → [CuCl4]2– + 6H2O
blue sol → yellow sol
equation of [Fe(H2O)6]3+ add excess Cl–
[Fe(H2O)6]3+ + 4Cl– → [FeCl4]– + 6H2O
orange sol → yellow sol
equation of [Al(H2O)6]3+ add excess Cl–
[Al(H2O)6]3+ + 4Cl– → [AlCl4]– + 6H2O
colourless sol → colourless sol