Question

Consider the standard electrode potential values(M²⁺/M) of the elements of the first transition series.

Ti	V	Cr	Mn	Fe
-1.63	-1.18	-0.90	-1.18	-0.44
Co	Ni	Cu	Zn
-0.28	-0.25	+0.34	-0.76

Explain:

(i) E⁰ value for copper is positive.

(ii) E⁰ value of Mn is more negative as expected from the trend

(iii) Cr³⁺ is a stronger reducing agent than Fe²⁺.

Answer 1

(i) The high energy to transform Cu(s) to Cu²⁺ (aq) is not balanced by its hydration enthalpy.

 (ii) Mn²⁺ has d⁵ configuration (stable half-filled configuration)

(iii) d⁵ to d³ occurs in case of Cr²⁺ to Cr³⁺ . More stable t³2g) while it change from d⁶ to d⁵ in case of fe²⁺ to fe^3+.