Question

The standard reduction potential of a silver electrode is .8 v.State whether it will act as cathode ir anide

Answer 1

When a metal is placed in a solution of its ions, the metal acquires either a positive or negative charge with respect to the solution. On account of this, a definite potential difference is developed between the metal and the solution. This potential difference is called electrode potential.

Electrode PotentialFor example, when a plate of zinc is placed in a solution having Zn2+ ions, it becomes negatively charged with respect to solution and thus a potential difference is set up between zinc plate and the solution. This potential difference is termed the electrode potential of zinc.

Similarly, when copper is placed in a solution having Cu2+ ions, it becomes positively charged with respect to solution. A potential difference is set up between the copper plate and the solution. The potential difference thus developed is termed as electrode potential of copper. The potential difference is estab­lished due to the formation of electrical double layer at the

Following two changes occur when a metal rod is dipped in its salt solution,  

(a) Oxidation: Metal ions pass from the electrode into solution leaving an excess of electrons and thus a negative charge on the electrode.

Oxidation

The conversion of metal atoms into metal ions by the attractive force of polar water molecules.

M →  Mn + ne-

The metal ions go into the solution and the electrons remain on the metal making it negatively charged. The tendency of the metal to change into ions is known as electrolytic solution pressure.

(b) Reduction: Metal ions in solution gain electrons from the electrode leaving a positive charge on the electrode. Metal ions start depositing on the metal surface leading to a positive charge on the metal.

Mn+ +  ne- →  M

In the beginning, both these changes occur with different speeds but soon an equilibrium is established.

M \rightleftharpoonsMn+ + ne-

In practice, one effect is greater than the other,

If first effect is greater than the second, the metal acquires a negative charge with respect to solution and

If the second is greater than the first, it acquires positive charge with respect to solution, thus in both the cases a potential difference is set up.

The magnitude of the electrode potential of a metal is a measure of its relative tendency to lose or gain electrons, i.e., it is a measure of the relative tendency to undergo oxidation (loss of electrons) or reduction (gain of electrons).