Based on standard electrode potential values,

Question:

Based on standard electrode potential values, suggest which of the following reactions would take place? (Consult the book for E\degree value).

(i) Cu + Zn2+→ Cu2+ + Zn

(ii) Mg + Fe2+→ Mg2+ + Fe

(iii) Br2 + 2Cl-→ Cl2 + 2Br-

(iv) Fe + Cd2+→ Cd + Fe2+

Solution:

(i) Cu + Zn2+→ Cu2+ + Zn

Here Cu undergoes oxidation so it acts as anode and Zn acts as the cathode. So from the table

For cathode E°cathode = -0.76 V

For anode E°anode = 0.52 V

E°cell = -0.24V

As the EMF of the cell is negative the given reaction will not occur spontaneously if they were to form a cell placed as electrodes.

(ii) Mg + Fe2+→ Mg2+ + Fe

Similarly, we can say that Mg undergoes oxidation and Fe undergoes reduction.

E°cathode = -0.44 V

E°anode = -2.36 V

E°cell = +1.92V

Positive EMF implies that the reaction will give out energy and attain stability, thus it will occur spontaneously. So the given redox reaction will occur.

(iii) Br2 + 2Cl-→ Cl2 + 2Br-

Here Br undergoes reduction thus acting as cathode and Cl acting as the anode.

For cathode E°cathode = 1.09 V

For anode E°anode = 1.36 V

E°cell = -0.25

The negative potential prevents easy reaction, so the redox reaction will not occur.

(iv) Fe + Cd2+→ Cd + Fe2+

Fe is the cathode and Cd is the anode

For cathode E°cathode = -0.44 V

For anode E°anode = -0.40 V

E°cell = -0.04v

The negative potential prevents easy reaction, so the redox reaction will not occur.

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