Daniell Cell Diagram & Working

The Daniell cell is a battery which is named after the British chemist and meteorologist John Frederic Daniell, who invented it in 1836.  The Daniell cell e.m.f. is 1.12 volt. This cell is used in experiments where a continuous and constant current is required.

Construction

The Daniell cell diagram is shown in figure 1. It consists of a cylindrical copper vessel containing a saturated solution of copper sulphate (CuSO4). To keep the solution saturated, it is provided with a shelf on which crystals of copper sulphate are placed. The copper vessel itself acts as a positive electrode. A porous pot containing dilute sulphuric acid (H2SO4) and an amalgamated zinc rod (impure zinc rod covered with a layer of mercury) is placed in the CuSOsolution. Zinc rod acts as a negative electrode.

Daniell Cell Diagram
Figure 1. Daniell Cell Diagram

Anode (negative electrode): Zinc (Zn) rod

Cathode (positive electrode): Copper (Cu) vessel

Depolariser: Copper sulphate (CuSO4)

Daniell Cell Working

When zinc rod and copper vessel are connected to the external circuit, the following reactions take place in the cell.

(a). Dilute H2SO4 acid dissociates into ions

H2SO4 → 2H+ + SO42−

(b). some of the zinc atoms go into solution as ions

Zn → Zn2+ + 2e

(c). Zn2+ ions and SO42− ions give ZnSO4

Zn2+ + SO42− → ZnSO4

combining equations (a), (b), and (c), we get

Zn + H2SO4 → ZnSO4 + 2H+ + 2e

The H+ ions diffuse through the porous pot and react with CuSO4 to give H2SO4 and Cu2+ ions are liberated i.e.

2H+ + CuSO4 → H2SO4 + Cu2+

These Cu2+ ions are deposited on the copper vessel making it positive with respect to the zinc electrode. Since CuSO4  is reacting with hydrogen ions (H+) to give liquid (i.e. H2SO4) so there is no polarization effect. Hence CuSO4  solution acts as a depolariser.

The e.m.f. of a Daniell cell is 1.12 Volt and its internal resistance is very low.

Frequently Asked Questions

  1. Why we use Daniell cell in an experiment in which continuous and constant supply of current is required?

    We use Daniell cell in an experiment in which continuous and constant supply of current is required because the concentration of CuSO4 remains the same, so the cell supplies continuous and constant current as e.m.f. of the cell remains constant.

  2. What do you mean by amalgamated zinc rod?

    The impure zinc rod covered with a layer of mercury is called amalgamated zinc rod.

  3. Name the depolariser used in the Daniell cell.

    The depolariser used in the Daniell cell is copper sulphate (CuSO4).

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