Cell reactions mercury zinc

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... 

Mercury cells, like dry cells, have a zinc anode and a use a mercuric oxide (HgO) cathode. The electrolyte is potassium hydroxide, KOH. These small, flat, metallic cells are widely used in watches, calculators, cameras, hearing aids, and other applications where small size is a premium. The reactions in the mercury cell are ... 

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,... 

The mercury battery is used extensively in medicine and electronic industries and is more expensive than the common dry cell. Contained in a stainless steel cylinder, the mercury battery consists of a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte containing zinc oxide and mercury(ll) oxide (Figure 19.8). The cell reactions are... 

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. 

The power density of the two batteries described is not enough to cope with miniature circuits, such as in watches and hearing aids. Batteries with very stable voltage and very long life are based on the zinc anode and a mercuric oxide cathode, with an alkaline electrolyte. They are known as mercury cells. The cell reaction is... 

Dry cells You are probably most familiar with the type of battery knows as the dry cell, which contains a moist paste in which the cathode half-reaction occurs. Three types of dry cells are the zinc-carbon dry cell, the alkaline cell, and the mercury cell. Zinc is oxidized in each of these dry cells. In the zinc-carbon dry cell, the zinc shell is the anode and a carbon rod is the cathode. The newer alkaline batteries are smaller than zinc-carbon dry cells. Mercury batteries are even smaller and are used in such devices as hearing aids and calculators. 

Despite its electrode potential (p. 98), very pure zinc has little or no reaction with dilute acids. If impurities are present, local electrochemical cells are set up (cf the rusting of iron. p. 398) and the zinc reacts readily evolving hydrogen. Amalgamation of zinc with mercury reduces the reactivity by giving uniformity to the surface. Very pure zinc reacts readily with dilute acids if previously coated with copper by adding copper(II) sulphate ... 

Metals are extremely important not only for chemical reactions but also for the health and welfare of plants and animals. Some examples of metals required for good nutrition, even in trace amounts, are iron, copper, cobalt, potassium, sodium, and zinc. Other metals—for example, mercury, lead, cadmium, barium, beryllium, radium, and uranium—are very toxic. Some metals at the atomic and ionic levels are crucial for the oxidation process that metabolizes carbohydrates for all living cells. 

The silver oxide and mercuric oxide button cells used in cameras and other devices requiring a miniature source of EMF consist of a zinc disk, which serves as the anode, and, on the other side of a porous separator, a paste of Ag20 or HgO. The reaction products are zinc hydroxide and metallic silver or mercury. Inert metal caps serve as the current collectors. 

This reaction, which takes place at open circuit, or as a side reaction during discharge of the battery, is detrimental in two ways it consumes one of the active materials in the cell, and it produces a gas that can build up pressure and eventually rupture the cell. This is the purpose of adding HgO to the zinc anode. In contact with metallic zinc, it is reduced to mercury, which amalgamates the zinc. The exchange... 

As well as having electrical conductivity, the transition elements can be used in the production of electrical energy through their chemical reactivity. Perhaps the most immediately familiar example is the dry cell battery. Any of a number of chemical reactions may be exploited in this context. As a consequence, manganese, nickel, zinc, silver, cadmium or mercury may be found in dry cells. 

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. 

In most cylindrical carbon—zinc cells, the zinc anode also serves as the container for the cell. The zinc can is made by drawing or extrusion. Mercury [7439-97-6] has traditionally been incorporated in the cell to improve the corrosion resistance of the anode, but the industry is in the process of removing this material because of environmental concerns. Corrosion prevention is especially important in cylindrical cells because of the tendency toward pitting of the zinc can which leads to perforation and electrolyte leakage. Other cell types, such as flat cells, do not suffer as much from this problem The anode reaction depends on the electrolyte used, but the charge-transfer step is... 

In 1865 Raoult measured the chemical (q) and voltaic (w) heat for several cells, the first by the heat of reaction in a Favre and Silbermann mercury calorimeter, and the second by a sine galvanometer (giving the e.m.f.) and a tangent galvanometer (giving the current) used simultaneously, with the e.m.f. of the Daniell cell as standard and unit quantity of electricity as that combined with i gm. of hydrogen or the equivalent of another ion. The product of these was equivalent to 23 9 kcal., and the heat evolved in precipitating copper by an equivalent of zinc was 23 2 kcal., nearly the same. But in other cases there were appreciable differences ... 

---