Video Transcript
What material is the anode of a mercury cell frequently made of? (A) Graphite, (B) zinc, (C) lead, (D) mercury, or (E) steel.
A mercury cell is a type of primary galvanic cell. Primary galvanic cells are single-use electrochemical cells where electrons are
generated spontaneously through a redox reaction. In the case of a mercury battery, these electrons pass through an external circuit in
a device such as a camera.
In a mercury cell, like other electrochemical cells, there is a reduction and
oxidation reaction. The reduction reaction in a mercury cell reduces mercury(II) oxide to neutral mercury
liquid by adding two electrons. Those two electrons must be generated in another reaction known as an oxidation. In the mercury cell, the oxidation and reduction reactions each occur in an isolated
half-cell. So the mercury reduction is in its own half-cell, and the oxidation reaction is in
its own half-cell.
The reaction must be energetically favorable so that it will occur spontaneously when
in the following overall reaction. As we can see from these equations, the metal that is typically used for the anode is
zinc. Zinc readily oxidizes, reducing two electrons to form Zn2+. The two electrons travel out of the cap of the battery and through a circuit on their
way to the mercury half-cell, where they then reduce the mercury.
So the material that the anode of a mercury cell is frequently made from is (B)
zinc.
