can i get more explaination about daniel cell

ras shurooqi, 13 years ago

Grade:12

1 Answers

Vijay Luxmi Askiitiansexpert

357 Points

13 years ago

Dear Ras,

The Daniell cell consists of a central zinc anode dipped into a porous earthenware pot containing a zinc sulfate solution. The porous pot is, in turn, immersed in a solution of copper sulfate contained in a copper can, which acts as the cell's cathode. The use of a porous barrier allows ions to pass through but keeps the solutions from mixing. Without this barrier, when no current was drawn the copper ions would drift to the zinc anode and undergo reduction without producing a current, which would destroy the battery's life.

Over time, copper buildup would block the pores in the earthenware barrier and cut short the battery's life. Nevertheless, the Daniel cell provided a longer and more reliable current than the Voltaic pile because the electrolyte deposited copper, which is a conductor, rather than hydrogen, which is an insulator, on the cathode. It was also safer and less corrosive. With an operating voltage of roughly 1.1 volts, it saw widespread use in telegraph networks until it was supplanted by the Leclanché cell in the late 1860s.

In the Daniell cell, copper and zinc electrodes are immersed in a solution of copper (II) sulphate and zinc sulphate respectively. At the anode, zinc is oxidized per the following half reaction:

Zn_(s) → Zn²⁺_(aq) + 2e^- .

At the cathode , copper is reduced per the following reaction:

Cu²⁺_(aq) + 2e^- → Cu_(s) .

The total reaction being:

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s).

In the Daniell cell which, due to its simplicity, is often used in classroom demonstrations, a wire and light bulb may connect the two electrodes. Electrons that are “pulled” from the zinc anode travel through the wire, providing an electrical current that illuminates the bulb. In such a cell, the sulphate ions play an important role. Having a negative charge, these anions build up around the anode to maintain a neutral charge. Conversely, at the cathode the copper (II) cations accumulate to maintain this neutral charge. These two processes cause copper solid to accumulate at the cathode and the zinc electrode to "dissolve" into the solution.

Since neither half reaction will occur independently of the other, the two half cells must be connected in a way that will allow ions to move freely between them. A porous barrier or ceramic disk may be used to separate the two solutions while allowing ion flow. When the half cells are placed in two entirely different and separate containers, a salt bridge is often used to connect the two cells. In the above wet-cell, sulfate anions move from the cathode to the anode via the salt bridge and the Zn2+ cations move in the opposite direction to maintain neutrality.