Mercury zinc, primary cell reactions

Primary cells. These are constructed of high-energy materials which react chemically and produce electrical power. The cell reaction is not reversible, and when the materials are consumed the device must be discarded. Typical examples of the primary cell are the ordinary flashlight battery (the LeClanche cell), and the zinc-mercury cells used in cameras, clocks, hearing aids, watches, and other familiar articles. 

Another important primary battery is the mercury cell. It usually comes in very small sizes and is used in hearing aids, watches, cameras, and some calculators. The anode of this cell is a zinc-mercury amalgam the reacting species is zinc. The cathode is a plate made up of mercury(II) oxide, HgO. The electrolyte is a paste containing HgO and sodium or potassium hydroxide. The electrode reactions are... 

The zinc-carhon, alkaline-zinc, and mercury cells are classified as primary batteries. Primary batteries produce electric energy by means of redox reactions that are not easily reversed. 

A third primary dry cell is the zinc-mercuric oxide cell depicted in Figure 17.7. It is commonly given the shape of a small button and is used in automatic cameras, hearing aids, digital calculators, and quartz-electric watches. This battery has an anode that is a mixture of mercury and zinc and a steel cathode in contact with solid mercury(II) oxide (HgO). The electrolyte is a 45% KOH solution that saturates an absorbent material. The anode half-reaction is the same as that in an alkaline dry cell,... 

Zinc-carbon, alkaline, and mercury cells are primary batteries, which are not rechargeable. Batteries that are rechargeable are called secondary batteries, or storage batteries. A storage battery produces energy from a reversible redox reaction, which occurs in the opposite direction when the battery is recharged. A nickel-cadmium rechargeable battery is an example of a secondary battery. 

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