Q.Define reference electrode. Write functions of salt bridge. Draw neat, labelled diagram of standard hydrogen electrode (SHE).

A reference electrode provides a fixed benchmark potential; the salt bridge keeps the circuit complete and both half-cells neutral; SHE is the standard zero-potential reference electrode.

Reference electrode: An electrode whose electrode potential is precisely known, constant and reproducible under standard conditions, used as a fixed benchmark against which the potential of another (unknown) electrode is measured. The standard hydrogen electrode (SHE) is the primary/universal reference electrode, arbitrarily assigned $E^\circ = 0.00\ V$; the saturated calomel electrode is a common secondary reference electrode.

Functions of the salt bridge:

1. It completes the electrical circuit of the galvanic cell by allowing ions to migrate between the two half-cells.
2. It maintains electrical neutrality in both half-cell solutions as the cell reaction proceeds, by supplying/removing ions as needed.
3. It minimises (eliminates) the liquid-junction potential that would otherwise arise if the two solutions were in direct contact. …