Long Answer TypeFor M2+/M and M3+/M2+ systems the E° values for some metals are as follows:
Cr2+/Cr – 0.9 V Cr3+/Cr2+ – 0.4 V
Mn2+/Mn – 1.2 V Mn3+/Mn2+ + 1.5 V
Fe2+/Fe – 0.4 V Fe3+/Fe2+ + 0.8 V
Use this data to comment upon
(a) The stability of Fe3+ in acid solution as compared to that of Cr3+ or Mn3+ and
(b) In case with which iron can be oxidised as compared to the similar process for either chromium or manganese metal
Predict which of the following will be coloured in aqueous solution? Ti3+, V3+, Cu+, Sc3+, Mn2+, Fe3+ and Co2+. Give reason for each.
A transition metal ion in coloured if it has one or more unpaired electron in (n-)d orbitals i.e. 3d orbitals in case of first transition series. When such species are exposed to visible radiation, d-d transition can take place.
In order to predict colour, let us examine (n – 1)d configuration of each specie.
|
Ti3+ |
3d1 configuration |
Species is coloured (purple) |
|
V3+ |
3d2 configuration |
Species is coloured (green) |
|
Cu+ |
3d10 4s°configuration |
Species is colourless. |
|
Sc3+ |
3d° 4s0 |
It does not contain unpaired e– in 3d orbitals. |
|
Mn2+ |
3d5 |
Colourles. It does not contain unpaired electron in 3d-orbitals coloured (pink). All 5 electrons unpaired in five 3d orbitals. |
|
Fe3+ |
3d5 |
Coloured (yellow). All 5 electrons unpaired in 3d orbitals. |
|
Co2+
|
3d7
|
Coloured (pink). Three e– unpaired in 3d-orbitals.
|
Short Answer TypeCompare the chemistry of actinides with that of the lanthanoids with special reference to:
(i) electronic configuration, (ii) atomic and ionic sizes, (iii) oxidation state (iv) chemical reactivity.
Long Answer TypeHow would you account for the following:
(a) Of the d4 species, Cr2+ is strongly reducing while manganese(III) is strongly oxidising.
(b) Cobalt(II) is stable in aqueous solution but in the presence of complexing reagents it is easily oxidized.
(c) The d1 configuration is very unstable in ions.
Short Answer Type
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