Bunshi na Voltaic da Kifin Saurarwa da Haɗaɗin Kifin Saurarwa a Bunshi na Voltaic

Amsa voltaic cell na gaba da karamin zinc plate da copper plate a cikin abinci mai sarre sulfuric acid. Kamar yadda ake nuna a cikin tushen, idan copper plate da zinc plate suna ce ta hanyar electrical load, zai faru electric current daga copper plate zuwa zinc plate har zuwa load. Yana nufin cewa akwai electrical potential difference an samu a kan copper plate da zinc plate. Idan current ya faru daga copper zuwa zinc, yana nufin cewa copper plate ya zama da tsari mai kyau da zinc plate ya zama da tsari mai faduwa.

Voltaic Cell Working

Principle of working of voltaic cell depends on the fact that, whenever two dissimilar metals are immersed in an electrolyte solution, the more reactive metal will tend 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.

The less reactive metal will attract the positive ions present in the electrolyte, and hence these positive ions get deposited on the plate making the plate positively charged. In this case of a simple voltaic cell, zinc comes out into the sulfuric acid solution as a positive ion and then reacts with the negative SO4 − − ion of the solution to form zinc sulfate (ZnSO4). As copper is less reactive, the positive hydrogen ions from the sulfuric acid solution tend to deposit on the copper plate. The more zinc ions that come out into the solution, the more electrons are left on the zinc plate. These electrons then pass through the external conductor connected between the zinc and copper plates.

When they reach the copper plate, these electrons combine with the hydrogen atoms deposited on the plate to form neutral hydrogen atoms. These atoms then combine in pairs to form molecules of hydrogen gas, which finally come up along the copper plate in the 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 0.62 Volt. During the operation of a voltaic cell, the zinc plate is at a lower potential with respect to the solution film adjacent to it, as shown in the figure below.

Similarly, when the Cu plate is placed in contact with the electrolyte, the positive hydrogen ions in the solution tend to deposit on it until its potential rises nearly to 0.46 V above that of the 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 to as polarization and local action.

Polarization of Voltaic Cell

It is observed that in this cell, the current gradually decreases and after a certain period of operation, the current may stop altogether. This decrease in current is due to the deposition of hydrogen on the copper plate. Although the hydrogen comes out of the cell in the form of bubbles, a thin layer of hydrogen still forms on the plate surface. This layer acts as an electrical insulator, thereby increasing the internal resistance of the cell. Because of this insulating layer, further hydrogen ions cannot get electrons from the copper plate and deposit in ionic form. This layer of positive hydrogen ions on the copper plate exerts a repulsive force on other hydrogen ions approaching the copper plate. Hence, the current decreases. This phenomenon is known as polarization.

Local Action of Voltaic Cell

It is found that even when the voltaic cell is not supplying any current, zinc continuously gets dissolved in the electrolyte. This is due to the fact that some traces of impurities like iron and lead in commercial zinc form tiny local cells which are short-circuited by the main body of zinc. The action of these parasitic cells cannot be controlled, so there is some wastage of zinc. This phenomenon is known as local action.

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