Coloured Complexes

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Iron(II) Hexaaqua [Fe(H2O)6]2+
pale green
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Cobalt(II) Hexaaqua [Co(H2O)6]2+
pink
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Copper(II) Hexaaqua [Cu(H2O)6]2+
pale blue
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Iron(III) Hexaaqua [Fe(H2O)6]3+
yellow/brown
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Aluminium(III) Hexaaqua [Al(H2O)6]3+
colourless (aluminium not actually a transition metal)
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Chromium Hexaaqua [Cr(H2O)6]3+
ruby
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[Fe(H2O)4(OH)2] (Fe(II))
green gelatinous ppt
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FeCo3 (Fe(II))
Green ppt
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[Co(H2O)4(OH)2]
blue ppt
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[Co(NH3)6]2+
pale yellow-brown solution
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CoCO3
pink ppt
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Cu(H2O)4(OH)2
pale blue ppt
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[Cu(NH3)4(H2O)2]2+
deep blue solution
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CuCO3
blue/green ppt
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[Fe(H2O)3(OH)3] (Fe(III))
Brown gelatinous ppt
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[Al(H2O)3(OH)3]
white ppt
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[Al(OH)4]-
colourless solution
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[Cr(H2O)3(OH)3]
green ppt
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[Cr(OH)6]3-
green solution
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[Cr(NH3)6]3+
purple solution
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Cr(OH)3
green ppt
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Why is the green ppt of [Fe(H2O)4(OH)2] often not seen?
it is oxidised by air to brown [Fe(H2O)3(OH)3]
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why is [Co(NH3)6]3+ pale yellow/brown solution often not seen?
it is oxidised by air to a dark brown mixture containing Co(III) compounds
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why are M3+ ions more acidic than M2+ ions?
because M3+ are smaller and more highly charged and therefore more strongly polarising. They can thus weaken one of the O-H bonds in one of the water molecules that surround them, releasing an H+ ion
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Why are all the compounds of Aluminium are colourless?
Aluminium is not a transition metal. It has no part filled d-orbitals. It is electrons moving between part filled d-orbitals that absorb light and make most transition metal compounds coloured
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Other cards in this set

Card 2

Front

pink

Back

Cobalt(II) Hexaaqua [Co(H2O)6]2+

Card 3

Front

pale blue

Back

Preview of the back of card 3

Card 4

Front

yellow/brown

Back

Preview of the back of card 4

Card 5

Front

colourless (aluminium not actually a transition metal)

Back

Preview of the back of card 5
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