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Four successive members of the first series of the transition metals are listed below. For which one of them the standard potential $(E^0_{M^{2+}/M})$ value has a positive sign?
A
Fe (Z = 26)
B
Co (Z = 27)
C
Ni (Z = 28)
D
Cu (Z = 29)
Detailed Solution
$E^0_{Fe^{2+}/Fe} = -0.44$ V, $E^0_{Co^{2+}/Co} = -0.28$ V, $E^0_{Ni^{2+}/Ni} = -0.25$ V
$E^0_{Cu^{2+}/Cu} = +0.34$ V
Copper has a high enthalpy of atomisation and a low hydration enthalpy, which are not balanced by its ionisation enthalpies, so only Cu has a positive value.
$E^0_{Cu^{2+}/Cu} = +0.34$ V
Copper has a high enthalpy of atomisation and a low hydration enthalpy, which are not balanced by its ionisation enthalpies, so only Cu has a positive value.