earlier, the electrons flow through the circuit from zinc to copper, where the Cu + ions in the solution accept the electrons, get reduced to copper and the same get deposited on the electrode. Here, the electrons are consumed and hence it is positive (+ve). Cu (aq) + 2e Cu (s) (gain of elect + - → ron-reduction) XII U9 Electro XII U9 Electro - - - - Salt bridge The electrolytes present in two half cells are connected using a salt bridge. We have learnt that the anodic oxidation of zinc electrodes results in the increase in concentration of Zn + in solution.
i.e., the solution contains more number of Zn + ions as compared to SO - and hence the solution in the anodic compartment would become positively charged. Similarly, the solution in the cathodic compartment would become negatively charged as the Cu + ions are reduced to copper i.e., the cathodic solution contain more number of SO - ions compared to Cu + . To maintain the electrical neutrality in both the compartments, the non reactive anions Cl - (from KCl taken in the salt bridge) move from the salt bridge and enter into the anodic compartment, at the same time some of the K + ions move from the salt bridge into the cathodic compartment. Completion of circuit Electrons flow from the negatively charged zinc anode into the positively charged copper cathode through the external wire, at the same time, anions move towards anode and cations are move towards the cathode compartment.
This completes the circuit. Consumption of Electrodes As the Daniel cell operates, the mass of zinc electrode gradually decreases while the mass of the copper electrode increases and hence the cell will function until the entire metallic zinc electrode is converted in to Zn + or the entire Cu + ions are converted in to metallic copper. Unlike Daniel cell, in certain cases, the reactants (or) products cannot serve as electrodes and in such cases inert electrode such as graphite (or) platinum is used which conducts current