The Daniel cell is a modified version of the voltaic cell. The polarization defect of the voltaic cell is overcome in the Daniel cell and can be considered as an improved version of the voltaic cell. Architecturally, the Daniel Cell is quite simple.
Construction of Daniell Cell:
It consists of a copper vessel filled with a concentrated solution of copper sulfate. Inside the container, there is a porous cylindrical vessel filled with dilute sulfuric acid, immersed in a copper sulfate solution. An amalgam zinc rod is immersed in dilute sulfuric acid in a porous vessel. According to the property of dilute electrolyte, sulfuric acid exists in its dilute form with positive hydrogen ions and negative sulfate ions. The sulfate ions come in contact with the electrons of the zinc rod and produce zinc sulfate through an oxidation reaction. As a result, the zinc rod becomes negatively charged and behaves like a cathode.
Positive hydrogen ions can cross the porous wall of the vessel and enter the copper sulfate solution where they combine with the sulfate ions of the copper sulfate electrolyte to form sulfuric acid. The positive copper ions of the copper sulfate electrolyte come in contact with the inner wall of the copper vessel where they pick up electrons through reduction and accumulate on the wall as copper atoms.
Working of Daniell Cell:
Allow us to make sense of the functioning rule of the cell bit by bit for better comprehension.
In weakened sulfuric corrosive arrangement there are H+ and SO4- – particles.
H+ ions pass through the porous vessel wall into the copper sulfate solution. The sulfate ions of dilute sulfuric acid react with zinc rod where Zn++ ions combine with SO4— ions to form zinc sulfate (ZnSO4). During this oxidation reaction, each zinc atom gives up two electrons in the zinc rod. Therefore, the zinc rod becomes negatively charged which means it behaves like the cathode of a battery.
The hydrogen particles (H+) present in the structure of the copper sulfate sequence are sulfuric acid (H2SO4) and the copper particles (Cu++) come from the mass of the outer shell of copper.
Copper ions are deposited on the wall of the copper vessel as copper metal by carrying electrons from the container. As a result, the copper container becomes positively charged i.e. the container is the anode of the Daniel cell. Now if we connect an external load between the central zinc rod and the peripheral copper container, the wall electrons start flowing from the zinc rod to the copper container.
In Daniel cell, we can avoid the polarization error which is the main drawback of voltaic cell. Since hydrogen gas does not accumulate at the anode because it forms sulfuric acid before reaching the anode (copper vessel wall), no layer of hydrogen will form on the anode to impede the reduction reaction.