For M2+/M and M3+/M2+ systems, the E⊖ values for some metals are as follows:
Cr2+/Cr -0.9V
Cr3/Cr2+ -0.4 V
Mn2+/Mn -1.2V
Mn3+/Mn2+ +1.5 V
Fe2+/Fe -0.4V
Fe3+/Fe2+ +0.8 V
Use this data to comment upon:
(i) The stability of Fe3+in acid solution as compared to that of Cr3+or Mn3+ and
(ii) The ease with which iron can be oxidised as compared to a similar process for either chromium or manganese metal.
(i) The E⊖ value for Fe3+/Fe2+ is higher than that for Cr3+/Cr2+and lower than that for Mn3+/Mn2+. So, the reduction of Fe3+to Fe2+is easier than the reduction of Mn3+to Mn2+, but not as easy as the reduction of Cr3+ to Cr2+. Hence, Fe3+is more stable than Mn3+, but less stable than Cr3+. These metal ions can be arranged in the increasing order of their stability as: Mn3+< Fe3+< Cr3+
(ii) The reduction potentials for the given pairs increase in the following order.
Mn2+ / Mn < Cr2+ / Cr < Fe2+ /Fe
So, the oxidation of Fe to Fe2+is not as easy as the oxidation of Cr to Cr2+and the oxidation of Mn to Mn2+. Thus, these metals can be arranged in the increasing order of their ability to get oxidised as: Fe < Cr < Mn value for Fe3+/ Fe2+ is higher than that for Cr3+/Cr2+and lower than that for Mn3+/Mn2+. So, the reduction of Fe3+to Fe2+is easier than the reduction of Mn3+to Mn2+, but not as easy as the reduction of Cr3+ to Cr2+. Hence, Fe3+is more stable than Mn3+, but less stable than Cr3+. These metal ions can be arranged in the increasing order of their stability as: Mn3+< Fe3+< Cr3+ (ii) The reduction potentials for the given pairs increase in the following order. Mn2+ / Mn < Cr2+ / Cr < Fe2+ /Fe So, the oxidation of Fe to Fe2+is not as easy as the oxidation of Cr to Cr2+and the oxidation of Mn to Mn2+. Thus, these metals can be arranged in the increasing order of their ability to get oxidised as: Fe < Cr < Mn
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Give simple chemical tests to distinguish between the following pairs of compounds.
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(iv) Toluene to benzyl alcohol
(v) Benzene to 4-bromonitrobenzene
(vi) Benzyl alcohol to 2-phenylethanoic acid
(vii) Ethanol to propanenitrile
(viii) Aniline to chlorobenzene
(ix) 2-Chlorobutane to 3, 4-dimethylhexane
(x) 2-Methyl-1-propene to 2-chloro-2-methylpropane
(xi) Ethyl chloride to propanoic acid
(xii) But-1-ene to n-butyliodide
(xiii) 2-Chloropropane to 1-propanol
(xiv) Isopropyl alcohol to iodoform
(xv) Chlorobenzene to p-nitrophenol
(xvi) 2-Bromopropane to 1-bromopropane
(xvii) Chloroethane to butane
(xviii) Benzene to diphenyl
(xix) tert-Butyl bromide to isobutyl bromide
(xx) Aniline to phenylisocyanide
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