PRIMARY CELLS
Cells which gives the electrical energy by irreversible chemical reaction is called primary cell .primary cells are not rechargeable.
VOLTAIC CELL
A voltaic cell consist of of copper and zinc electrodes dipped in dilute sulphuric acid.The positive charges accumulate on the copper electrode and negative charges on the zinc electrode.This is because the electrolyte decomposes in to H ions and Sulphate ions. The negatively charged sulphate ions move towards Zn and Zn loses two electrons and become ZnSO4 .Positively charged Hydrogen ions move towards Cu and accept two electrons and hydrogen gas is liberated.
When the circuit is closed the Cu is at higher potential and Zn is at lower potential. Current flows from Cu electrodes to Zn electrode in the external circuit. The emf of the cell is 1V.
DANIEL CELL
Danial cell consist of a copper vessel containing copper sulphate solution. The wall of the vessel is the positive electrode. A porous pot containing dilute sulphuric acid is placed in the CuSO4 solution. The Zinc rod is immersed in dilute sulphuric acid. This is the negative electrode.
The porous pot allows the ions to pass from one solution to other but prevents the mixing of the solutions.Oxidation take place at Zinc rod.The Zinc ions move to the copper sulphate solution through the porous pot and combine with sulphate ion to form zinc sulphate.
Cu ions move towards the copper vessel and are deposited there.The reduction reaction take place
diagram
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