Dry Cell : Structure, Working, Chemical Reactions & Its Applications

A dry cell is the simplest form of electricity-producing source. A number of cells combined cells together forms a battery. The lead-acid or nickel-cadmium battery is the advanced version of dry cell. This cell was first invented by French engineer Georges Leclanche in the year 1866. His invention was named after his name as Leclanche battery. But at that time, it was very heavy and could be easily broken. A dry cell has the same principle and it is the advanced version of the Leclanche battery and comes in different voltage and sizes. The commercial form of the zinc-carbon cell which is the modified form of the Leclanche battery was invented in 1881 by Carl Gassner of Mainz. It is produced in great quantities and used in many applications like toys, radios, calculators, etc.

What is a Dry Cell?

A dry cell is a device that generates electricity based on chemical reactions. When the two electrodes of the cell are connected via a closed path, then the cell forces the electrons to flow from one end to the other. The flow of electrons causes the current to flow in the closed circuit.

With the help of chemical reactions, the electrons flow from one end to the other. When two or more cells, connected with correct polarity, more electrons are flowed due to high potential. This combination is called a battery. From a minimum voltage of 1.5 V to 100 V, a battery can be used to obtain a range of voltages. Even the output DC voltage of the battery can be regulated to different levels using power electronic converters like chopper circuits.

Structure of  Cell

The structure of the zinc-carbon dry cell is shown in the figure. It consists of the anode terminal as zinc or in general graphite rod. The carbon forms the cathode terminal. It may be observed that in older versions of dry cell the zinc was used as cathode and graphite was used as anode terminal. The selection of the elements is fundamentally based on its chemical configuration of the outermost orbit of the elements.

If it has more number electrons in the outermost orbit, then it can act as a donor, and hence forms the cathode. Similarly, if the outermost orbit has fewer electrons, it can easily accept and hence forms the anode. The electrolyte placed in between acts as a catalyst for the chemical reactions. In general, we use ammonium chloride jelly as the electrolyte. In the figure shown, the electrolyte used is a mixture of zinc and chloride. Also, sodium chloride is also used as an electrolyte. A mixture of manganese dioxide and carbon is surrounded around the anode rod.

The whole configuration is placed in a metal tube. The jelly is prevented from drying up by using a pitch at the top of the cell. A carbon washer is placed at the bottom. The purpose of this washer is to prevent the zinc anode rod from coming in contact with the container.

This is also called a spacer as shown in the diagram. The zinc can is also surrounded by paper insulation for insulation purposes. For large batteries, other insulating materials such as mica, etc. are also used. The positive terminal of the ell is formed at the top. The negative terminal of the cell is formed at the base.

Working of Dry Cell

A dry cell fundamentally works on chemical reactions. Due to the reactions that take place between the electrolyte and the electrodes, the electrons flow from one electrode to the other. Substances such as acids dissolve in water to form ionized particles. The ionized particle is of two types. The positive ions are called cations and the negative ions are called anions. The acids which are dissolved in water are called electrolytes.

In the above-mentioned diagram, the zinc chloride forms as the electrolyte. Similarly ammonium chloride jelly also forms as an electrolyte. The metal rods immersed in electrolytes form electrodes. Based on the chemical characteristics of the metal rods, we have a positive electrode as anode and a negative electrode as the cathode.

The electrodes attract the oppositely charged ions to their side. For example, the cathode attracts the anions and the anode attracts the cations. In this process the electrons flow from one direction to the other, hence we get a flow of charges. This is called current.

Chemical Reactions

The reactions taking place in the cell is shown below. First is the oxidation reaction.

In this, the zinc cathode is oxidized to positively charged zinc ions releasing two ions. These electrons are collected by the anode. Then comes the reduction reaction.

The reduction reaction at the anode is shown above. This reaction produces an electric current. It releases oxide ions with magnesium oxide. This reaction forms when magnesium is combined with the electrolyte.

The other two reactions represent an acid-base reaction and precipitation reaction taking place in the dry cell. In the acid-base reaction, NH is combined with OH to produce NH3 along with water. The outcomes are NH3 and water base.

Difference Between a Dry Cell and Wet Cell

The main difference between the dry cell and the wet cell is the form of electrolyte. As discussed before, in a dry cell, the electrolyte such as ammonium chloride is dry in nature. Such dry cells are more common and used in toys, radios, etc. But in a wet cell, the electrolyte is in the liquid state.

Liquid electrolytes such as sulfuric acid, which is a dangerous corrosive liquid is used. Due to the nature of such liquids, the wet cell is more explosive in nature and needs to be handled with care. The best advantage of such wet cells are they can b easily recharged and used for numerous applications. Such batteries find common usage in aviation, utilities, energy storage, and cell phone towers.

Dry Cell Functions

The dry cell function based on the chemical reactions between the electrode and the electrolytes. When the electrodes are placed in the electrolytes, it attracts the oppositely charged ions towards themselves. This causes the flow of charges, and hence current is produced.

Advantages 

The advantages of the dry cell include the following.

• The dry cell has numerous advantages such as
• It is small in size.
• It can come in a variety of voltage levels.
• It is handy and has numerous applications.
• It is the only source of DC voltage.
• It can be used along with power electronic circuits to regulate the output voltage
• It is rechargeable.

Disadvantages

The disadvantages of the dry cell include the following.

• It must be handled with care
• It is explosive
• Large rating batteries are very heavy

Applications

The applications of the dry cell include the following.

• Toys
• Aviation
• Cell phones
• Radio
• Calculator
• Watches
• Hearing Aids

Hence we have seen the operation, classification, and applications of the dry cells. One interesting point to be noted is the battery works only when the electrodes are physically in touch with each other. There must exist a conducting medium between the two electrodes. The question is can water be used as a conducting medium between the electrodes of the dry cell? In that case, what will happen if this cell is dipped in water?