question_answer 74)

  On the basis of standard electrode potential values, suggest which of the following reactions would take place? (Consult the book for \[{{E}^{O-}}\] value). (i) \[Cu+Z{{n}^{2+}}\to C{{u}^{2+}}+Zn\] (ii) \[Mg+F{{e}^{2+}}\to M{{g}^{2+}}+Fe\] (iii) \[B{{r}_{2}}+2C{{l}^{-}}\to C{{l}_{2}}+2B{{r}^{-}}\] (iv)\[Fe+C{{d}^{2+}}\to Cd+F{{e}^{2+}}\]

Answer:

  (i) \[Cu+Z{{n}^{2+}}\to C{{u}^{2+}}+Zn\] \[E_{\operatorname{Re}dox\,process}^{{}^\circ }=E_{\operatorname{Re}duced\,species}^{{}^\circ }-E_{Oxidised\,species}^{{}^\circ }\]                 \[=E_{Z{{n}^{2+}}/Zn}^{{}^\circ }-E_{C{{u}^{2+}}/Cu}^{{}^\circ }\]                 \[=(-0.76)-(+0.34)=-1.10V\] Negative value shows that the redox process is not feasible. (ii) \[Mg+F{{e}^{2+}}\to M{{g}^{2+}}+Fe\] \[E_{\operatorname{Re}dox\,process}^{{}^\circ }=E_{\operatorname{Re}duced\,species}^{{}^\circ }-E_{Oxidised\,species}^{{}^\circ }\]                       \[=E_{F{{e}^{2+}}/Fe}^{{}^\circ }-E_{M{{g}^{2+}}/Mg}^{{}^\circ }\]                 \[=-0.44-(-2.36)=+1.92V\] Positive value shows that the redox process is feasible. (iii)  \[B{{r}_{2}}+2C{{l}^{-}}\to C{{l}_{2}}+2B{{r}^{-}}\]                 \[E_{\operatorname{Re}dox\,process}^{{}^\circ }=E_{\operatorname{Re}duced\,species}^{{}^\circ }-E_{Oxidised\,species}^{{}^\circ }\]                                                 \[=E_{B{{r}_{2}}/Br}^{{}^\circ }-E_{C{{l}_{2}}/C{{l}^{-}}}^{{}^\circ }\]                                                 \[=+1.09-1.36=-ve\] Negative value shows that the redox process is not feasible. (iv)   \[Fe+C{{d}^{2+}}\to Cd+F{{e}^{2+}}\]                        \[E_{\operatorname{Re}dox\,process}^{{}^\circ }=E_{\operatorname{Re}duced\,species}^{{}^\circ }-E_{Oxidised\,species}^{{}^\circ }\]                                 \[=E_{C{{d}^{2}}/Cd}^{{}^\circ }-E_{F{{e}^{2+}}Fe}^{{}^\circ }\]                                 \[=(-0.40)-(-0.44)=+0.04V\] Positive value shows that the redox process is feasible.