In this topic, you study the construction and working of Daniel cell.
It is a double fluid cell. Figure 9.6 shows the construction of the Daniel cell. It consists of an outer copper vessel, which works as positive pole Of the cell. It contains saturated solution Of CuS04 crystals placed in the perforated shelves as shown in Fig. 9.6.
Fig. 9.6. Daniel cell.
Fig. 9.7. Bunsen cell.
A porous pot is placed inside the vessel. It contains the electrolyte dilute H2S04 and an amalgamated Zn rod. The Zn rod acts as the negative terminal of the cell.
Working. On completing the circuit, the Zn rod reacts with dilute H2S04 and forms nascent hydrogen.
Zn + H2S04 znS04 + 2H
The hydrogen is positively charged and travels towards the copper. This hydrogen after gaining two electrons liberates. This hydrogen will react with the saturated solution of CuS04 and forms
cuS04 + H2 cu + H2S04
Thus the defect of polarization is removed. The Zn rod is amalgamated so the defect of local action is also removed.
Uses. This has an e.m.f. of 1.1 V. It gives constant I e.m.f. It is mostly used in laboratories etc.
Note. Sometimes it is also called the Daniel gravity cell. In this cell both the electrolytes are placed in thé same container. There is no porous pot but because of the gravity of the liquids, the dil. H2S04 has less gravity so it is on the upper portion and CuS04 solution in the bottom. The Zn rod reacts with the dil. H2S04 and CuS04 there works as the depolarizer.