It is designed to make use of the spontaneous redox reaction between zinc and cupric ions to produce an electric current. It consists of two half-cells. The half-cells on the left contain a zinc metal electrode dipped in ZnSO4 solution.
The half-cell on the right consists of the copper metal electrode in a solution CuSO4. The half-cells are joined by a salt bridge that prevents the mechanical mixing of the solution.
When the zinc and copper electrodes are joined by a wire, the following observations are made:
During the passage, if the electric current through the external circuit, electrons flow from the zinc electrode to the copper electrode. At the zinc electrode, the zinc metal is oxidized to zinc ions which go into the solution.
The electrons released at the electrode travel through the external circuit to the copper electrode where they are used in the reduction of Cu2+ ions to metallic copper which is deposited on the electrode. Thus, the overall redox reaction is:
Zn(s) + Cu2+ → Cu(s) + Zn2++(aq)
Thus, indirect redox reaction leads to the production of electrical energy. At the zinc rod, oxidation occurs. It is the anode of the cell and is negatively charged while at the copper electrode, reduction takes place; it is the cathode of the cell and is positively charged.
Thus, the above points can be summed up as:
|Oxidation half reaction||Reduction half reaction||Net reaction|
Zn(s) → Zn2+(aq) + 2e-
Cu2+(aq) + 2e- → Cu (s)
Zn(s) + Cu2+ (aq) → Zn2+(aq) + Cu(s)
The signs of the anode and cathode in the voltaic or galvanic cells are opposite to those in the electrolytic cells.
Volatic or Galvanic Cell
E.m.f. is applied to cell
E.m.f. is generated by cell
Voltaic or Galvanic cell
Daniell cell has the emf value 1.09 volt. If an opposing emf exactly equal to 1.09 volt is applied to the cell, the cell reaction,
Zn + Cu2+→ Cu + Zn2+
stops but if it is increased infinitesimally beyond 1.09 volt, the cell reaction is reversed.
Cu + Zn2+→ Zn + Cu2+
Such a cell is termed a reversible cell. Thus, the following are the two main conditions of reversibility:
Among other cells, a galvanic cell is a type of electrochemical cell. It is used to supply electric current by making the transfer of electrons through a redox reaction. A galvanic cell is an exemplary idea of how energy can be harnessed using simple reactions between a few given elements. It is amazing to study how a galvanic cell can be set up and utilized to obtain energy.
Explaining in the most simple terms, a galvanic cell acts as a device in which simultaneous oxidation and reduction reactions take place. These reactions are used to convert chemical energy into electrical energy, which can be utilized for any commercial purpose.
In order to create a galvanic cell, one would have to go through the following setup. The cell would ideally include two electrodes. One of these electrodes, the cathode, shall be a positively charged electrode while the other, shall be the anode, the negatively charged electrode.These two electrodes shall form the two essential components of the galvanic cell. The chemical reaction related to reduction shall take place at the cathode while the oxidation half-reaction shall take place at the anode. As has already been said, any two metals can be used to create a chemical reaction.
Let us take an example where the two metals involved in the chemical reaction are zinc and copper. As the chemical reaction takes place, Zinc would end up losing two electrons. This will be taken up by copper to become elemental copper.Since these two metals will be placed in two separate containers and would be connected by a conducting wire, an electric current would be formed, which would transfer all electrons from one metal to another.
Some of the important terms brought into use in galvanic cells are listed below:Phase boundaries: It refers to the two metals which act as cathode and anode.
Salt bridge: The connecting bridge or medium that allows a redox reaction to take place.
Oxidation and reduction: The chemical processes that allow the electric current to form and flow through a galvanic cell.
Q1. In a galvanic cell, what would happen if no salt bridge is used while the redox reaction takes place?
Ans: In the absence of a salt bridge within each container containing the metals, the redox reaction would begin in much the same way. But in the absence of the salt bridge, the same would come to an end rather abruptly. The respective solutions will not be able to maintain their electric neutrality. Other than this, there will be no change in the chemical reaction or any alteration of any type because of the absence of the salt bridge or medium.