- Simple Voltaic Cell Definition: A simple voltaic cell is made by immersing zinc and copper plates in a diluted sulfuric acid solution, generating electricity.
- Working Principle: The cell works because dissimilar metals in an electrolyte create a potential difference, causing electron flow.
- Electron Movement: Electrons move from the zinc plate to the copper plate through an external circuit, generating current.
- Polarization: Hydrogen buildup on the copper plate reduces current by increasing resistance, known as polarization.
- Local Action: Impurities in zinc cause unwanted reactions that waste zinc, even when the cell is not producing current.
A simple voltaic cell is made by placing a zinc plate and a copper plate in a diluted sulfuric acid solution. When the plates are connected through an external load, electric current flows from the copper plate to the zinc plate. This creates an electrical potential difference, making the copper plate positively charged and the zinc plate negatively charged.
Voltaic Cell Working
The working principle of a voltaic cell is based on immersing two different metals in an electrolyte solution. The more reactive metal dissolves into positive ions, leaving behind electrons on the metal plate, making it 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.
When electrons reach the copper plate, they combine with hydrogen ions to form neutral hydrogen atoms. These atoms pair up to form hydrogen gas molecules, which appear as bubbles on the copper plate. The chemical action 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.
Polarization of Voltaic Cell
In this cell, the electric current slowly decreases and may eventually stop. This happens because hydrogen builds up on the copper plate, forming a thin insulating layer. This layer increases the cell’s resistance, blocking further hydrogen ions from reaching the copper plate to receive electrons, thus reducing the current. 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 that there is some wastage of zinc. This phenomenon is known as local action.
