Voltaic Cell Basic Construction and Working of Voltaic CellPublished on 24/2/2012 and last updated on 5/9/2018
Voltaic Cell WorkingThe working principle of voltaic cell depends upon the principle that, whenever two dissimilar metals are immersed inside an electrolyte solution, the more reactive metal will have a tendency to dissolve in the electrolyte as positive metal ions, leaving electrons behind on the metal plate. This phenomenon makes the more reactive metal plate negatively charged. Less reactive metal will attract positive ions present in the electrolyte, and hence these positive ions get deposited on the plate making the plate positively charged. Here in this case of simple voltaic cell, the zinc comes out in the sulfuric acid solution as positive ion and then reacts with negative SO4 − − ion of the solution and forms zinc sulfate (ZnSO4). As the copper is less reactive metal, the positive hydrogen ions of the sulfuric acid solution have a tendency to get deposited on the copper plate. More zinc ions coming out in the solution means more number of electrons leave in the zinc plate. These electrons then pass through the external conductor connected between zinc and copper plates.
On reaching on the copper plate, these electrons then combine with the hydrogen atoms deposited on the plate and form neutral hydrogen atoms. These atoms then combine in pairs to form molecules of hydrogen gas and the gas lastly comes up along the copper plate in form of hydrogen bubbles. The chemical action taking place inside the voltaic cell is as follows, However, this action stops when the contact potential between Zn and dilute sulfuric acid reaches the value of 0.62 Volt. During operation of a voltaic cell, the zinc late is at a lower potential with respect of the solution film adjacent to it as shown in the figure below.
Similarly, when Cu plate is placed in contact with the electrolyte, then the positive hydrogen ions in the solution have a tendency to get deposited on it until its potential rises nearly to 0.46 V above that solution. Hence, the electrical potential difference developed in a voltaic cell is 0.62 − (− 0.46) = 1.08 Volts. In a simple voltaic cell there are mainly two drawbacks, referred as polarization and local action.