Representation or formulation of galvanic cells

Representation or formulation of a galvanic cells

 A galvanic cell is represented by a short notation or diagram which includes electrodes, aqueous solutions of ions, and the other species that may or may not be involved in the cell reaction. 

The following conventions are used to write the cell notation: 

(i) The metal electrodes or the inert electrodes (used as a conducting device in case of gas electrodes) are placed at the ends of the cell formula. The anode (-) is written at the extreme left and cathode (+) is placed at the extreme right of the cell notation. 

(ii) The insoluble substances if any or gases are placed in the interior positions adjacent to the metal electrodes. 

(iii) The aqueous solutions of ions are placed at the middle of the cell formula. 

(iv) A single vertical line is used between two phases to indicate the phase boundary, such as that between the solid electrode and the aqueous solution of ions. It represents the direct contact between them. 

(v) A double vertical line is used between two solutions to indicate that they are connected by a salt bridge. 

(vi) The additional information such as concentration of solutions and the gas pressure is also given. 

(vii) The ions in the same phase are separated by a comma. 

For example, Fe3+,Fe2+ l Pt 

(viii) A single half cell is written in the order, an aqueous solution of ions first, and the solid electrode. 

For example, Zn²⁺(1M) | Zn.

This order is reversed when the electrode acts as an anode in the galvanic cell. 

The following examples will illustrate these conventions: 

(i) The cell composed of Mg(anode) and Cu(cathode) consists of two half cells, Mg²⁺(1M) l Mg and Cu²⁺(1M) | Cu. 

It is formulated as Mg(s) | Mg²⁺(1M) || Cu²⁺(1M) | Cu 

(ii) The notation for the cell consisting of 

H⁺(1M) | H₂(g 1atm) | Pt and Ag⁺(1M) | Ag(s) half cells with hydrogen gas electrode as anode and Ag electrode as cathode will be,

Pt | H₂(g, 1atm) | H⁺(1M) || Ag⁺(1M) | Ag(s).