Chemical Effect of Current
Michael Faraday, the great British experimental physicist, began his experiments on the passage of electricity through liquids, in 1834.
Faraday's Laws of Electrolysis
- First law states that the mass of a substance deposited or liberated on an electrode during electrolysis is proportional to the total quantity of electric charge passed through the electrolyte.
- Second law states that if same quantity of charge is passed through several electrolytes, the mass of substance deposited or liberated at electrodes is proportional to their chemical equivalent (equivalent weight)
The Process of Electrolysis
The above statements are the conclusions made by Faraday after conducting a number of experiments on 'electrolysis'. The process of electrolysis is carried out in an apparatus called voltameter.
If the electrolyte is a solution of copper sulphate (CuSO4) and the electrodes are copper plates, it is called a copper voltameter. On the other hand if the electrolyte is a solution of silver nitrate AgNO3 and electrodes are silver plates it is called a silver voltameter. When appropriate direct potential difference is applied across the electrodes, the electrolyte starts conducting current. Faraday's second law is illustrated in the figure where silver and copper voltameters are connected in series. For a given time, the same charge will pass through each voltameter. It will be seen that the masses of silver (Ag) and copper (Cu) deposited on the respective cathodes are in the ratio of 108:32. These values of 108 and 32 are called the chemical equivalents of silver and copper respectively.
Electroplating of Silver
Secondary cell is a cell in which chemical action is reversible. (e.g., lead acid accumulator, alkali accumulator). Many chemical reactions take place and energy is released. If this happens in an electrolyte, with one or more of the ionic species in it as participants, it is then possible that the energy released directly and solely increases the electrical potential energy of the ions. The chemical reaction is thus a source of electrical energy. The system can be used as a source of electrical power if the chemical reaction proceeds at a steady rate. This is what one tries to achieve in an electrochemical cell.
Wet Leclanche Cell
Therefore the carbon rod forms the positive pole and the zinc rod the negative pole. When the carbon rod and zinc rod are connected by a wire, the current flows from carbon to zinc through the wire.