Electricity can be used for various purposes it can be mechanical, physical and chemical work. In this article we emphasis on the chemical effects of current its effects on chemical reactions. A chemical reaction may not be spontaneous; however on supplying energy to it, the reaction becomes spontaneous. For example no reaction take places on melting of NaCl . But on supplying electrical energy to molten NaCl, Na+ and Cl- ions start moving towards the electrodes. Cl- ion lose electron to form cl atoms, that is , undergo oxidation whereas Na+ ions gain electron to form Na+ atoms that is undergo reduction. Thus, redox reaction occurs on absorbing electrical energy which was otherwise non – spontaneous. The flow of current due to movement of ions is called electrolytic conduction. The phenomenon is called electrolysis.
Electrolysis maybe defined as a process of decomposition of electrolyte by the passage of electricity through its aqueous solution or molten state. The apparatus used to bring electrolysis is known as electrolytic cell. It consists of glass vessel in which electrolyte in the form of an aqueous solution or in molten state is taken. Two metal rods are dipped into it and are connected to a source of energy that is battery these rods are called as electrodes; the one connected to the negative pole of the battery is called cathode and the other connected to the positive pole of the battery is called anode.
Mechanism of Electrolysis
The process of electrolysis can be explained on the basis of ionization theory. According to this theory whenever electrolyte is dissolved in water or is taken in molten state the electrolyte dissociates to produce positive and negative charged ions. On passing electric current, the positive charged ions move towards cathode and hence are called cations whereas negative charged ions move towards anode and hence are called anions. On reaching their respective electrodes ions lose their charge and become neutral particles. The cations accept electrons from cathode to become neutral particles whereas anions give electrons to anode to become neutral particles. Thus oxidations occur at anode while reduction takes place at cathode. The conversion of ions particles at their respective electrode is called primary change. The product formed as a result of primary change maybe collected as such or it may undergo a secondary change to form final product.
Further when electrolysis of an electrolyte is carried out in molten state, the product of electrolysis is actually the substances obtained from the ions of the electrolyte. But the situation is not simple when electrolysis of an electrolyte is carried out in aqueous solution. This is due to the reason that in aqueous solution, besides the ions of electrolyte which are present in large amounts,, there are also H+ and OH- ions are furnished by slight ionization of water. Consequently, when electric current is is passed both cations of electrolyte and H+ ions of water, would move towards cathode while the anions of the electrolyte and OH- from water move towards the anode. So two ions are present at each of the electrode. But the ion which will be discharged depends on:-
- Upon ions respective discharge potentials
- Sometimes on the material of electrode