Question

iv) Describe the construction and working of
the standard hydrogen electrode (S.H.E.).
Give its advantages and disadvantages.​

Answer 1

Answer:

It consists of a thin rectangular platinum foil which is coated with fresh platinum black to increase the adsorption capacity of the metal. This is welded and the end of it is fused into the inner tube through the base. In the inner tube, little mercury is taken and a Cu wire is introduced to make the external electrical contact. The inner tube is enclosed in an outer jacket having an inlet tube for sending in H2 gas and has a perforated wider base for the escape of excess of H2. This unit is dipped in HCl taken in a beaker such that the metal foil remains in the solution.

Working

When pure and dry H2 gas is passed through the inlet tube, a part of the gas gets adsorbed and the excess bubbles out through the perforations. Between the H2 gas absorbed on the surface of the metal and H+ of the solution, an equilibrium is established and an electrical double layer of opposite charges is formed. The potential developed is called H2 electrode potential.

In the above system, when the H2 gas at a pressure of 1atm is bubbled through 1M HCl, the electrode (constructed) or formed is called STANDARD HYDROGEN ELECTRODE (SHE) or Normal H2 electrode (NHE). This is represented as Pt, H2 / H+(760 mm of Hg) (IM)

The standard H2 electrode potential is defined as the potential that is developed between the H2 gas adsorbed on the pt metal and H+ of the solution when the H2 gas at a pressure of 760 mm of Hg is in equilibrium with H+ of unit concentration

The magnitude of SHE potential is considered to be zero. It is used-

1) For the determination of electrode potential of metal electrode system.

2) For the determination of pH of the solution.

Limitations

1) It is rather difficult to regulate the pressure of the H2 gas to be at exactly 1atm throughout the experiment.

2) Excess of H2 bubbling out carries little HCl with it and hence the H+ concentration decreases. In such a system, it is difficult to maintain the concentration of HCl at 1M.

3) Platinum foil gets easily poisoned by the impurities present in the gas and HCl. In fact, the attainment of equilibrium is ensured by trial and error.

4) If the solution contains any oxidizing agent, the H2 electrode cannot be used.

Answer 2

A standard hydrogen electrode is a working electrode that is being used to figure out a cell's electrode potential.

Construction and working of  the standard hydrogen electrode :

• The Standard Hydrogen Electrode, or SHE for abbreviation, is an electrode that works as a base line in the electrochemical second reaction which is used to calculate the potential value of various atomic orbitals. The hydrogen gas contained in this half-cell has a pressure of 1 bar.

• A standard hydrogen electrode is a working electrode that is being used to figure out a cell's electrode potential.

• A standard hydrogen element is made by passing purified hydrogen gas at atmospheric pressure through a solution of 1mol/L Hydrogen ion in conjunction with coated glass foil.