Main Difference – Dry Cell vs Wet Cell
An electric cell is known as a device which is capable of converting one form of energy to another, often chemical energy to electricity. Dry cell and wet cell are two types of cells whose main difference lies in their physical state; Electrolytes in a dry cell are moist solids whereas electrolytes in a wet cell are liquids. However, before looking at the difference between dry cell and wet cell further, it is important to understand the structure of a cell.
This article explores,
1. What is the Structure of a Cell
2. What is a Dry Cell
– Characteristics, Properties, Examples
3. What is a Wet Cell
– Characteristics, Properties, Examples
4. What is the difference between Dry cell and Wet Cell
What is the Structure of a Cell
A cell is composed of electrodes and electrolytes. As a result of the chemical reactions between these electrodes and electrolytes, an electric potential is created between the electrodes. This potential depends on the nature of electrodes and electrolytes. A combination of several such cells is called a battery. The cells of a battery can be connected either in parallel or in serial. The number of cells, type of cells and type of combination determines the potential difference between the two ends of a given battery.
Cells can be divided into two main categories based on their electrical properties:
Primary Cells
The chemical reaction which is responsible for energy generation is irreversible. Therefore, it cannot be recharged and should be disposed of after using. These contain solid electrolytes adsorbed onto a solid material. Therefore, primary cells are mostly dry cells.
Secondary Cells
Reversible chemical reactions power secondary cells, and therefore it is possible to be recharged. This can be done by an external power source.
Cells are also distinguished as dry and wet cells based on the physical state of the electrolytes present in the cell.
What is a Dry Cell
Dry cell batteries are in the form of a moist paste. The extent of moisture is just enough for the electric current to flow. A dry cell can be used in any orientation and be handled easily as the chemicals inside will not spill out. The most common battery which contains dry cells is Zinc-Carbon battery. It consists of a carbon rod as the cathode with an outer Zn shell, which is the anode. The carbon rod is covered with a paste of MnO2 and C. The electrolyte NH4Cl is a moist paste. Alkaline batteries are made by replacing NH4Cl by KOH.
Other most common Dry Cell batteries are Lithium batteries which are commonly found in mobile phones, laptops, digital cameras and sometimes cars. Lithium cobalt cathodes with carbon anodes are abundant.
Dry cells are used for longer periods of storage as their discharge rate is lower. These are typically primary cells. However, some wet cells can act as secondary cells as well.
Dry cell batteries should be disposed of in a proper manner since they can cause harmful effect to environment and people.
Figure 1: Zinc Carbon Battery
What is a Wet Cell
Wet cells are the first born of the electrical cell family. The term ‘wet’ arises from the fact that the electrolytes of the cell are present as liquids. Most of the time, the liquid consists of a solution of sulphuric acid and water. These are also called vented/flooded acid batteries. Common examples are lead-acid batteries, which are known as car batteries. The electrodes are made of lead dioxide, and metallic lead whereas the electrolyte is sulphuric acid. Insulator sheets are used to separate the electrodes and the electrolyte.
Wet cells can be either primary or secondary. Daniel cell, Leclanche cell, Grove cell, Bunsen cell, Chromic acid cell, Clark cell and Weston cell are known as primary cells. These cannot be recharged. The car battery is a secondary wet cell.
There are several drawbacks of wet cells, the main drawback being the liquid state of the electrolytes, which might leak or spill out if the outer covering is damaged and cause harm if a person comes into contact with such corrosive chemicals. Further, batteries consisting of wet cells are heavy, making it difficult to handle them.
Figure 2: Zn-Cu Galvanic Cell
Difference Between Dry Cell and Wet Cell
Physical State of Electrolytes
Dry Cell: Electrolytes are moist solids.
Wet Cell: Electrolytes are liquids.
Leaking
Dry Cell: There is no leaking of chemicals.
Wet Cell: There is a tendency for corrosive chemicals to be leaked.
Size
Dry Cell: Dry cells are small.
Wet Cell: Wet cells are large.
Ease of Handling
Dry Cell: Dry cells are easy to handle.
Wet Cell: Wet cells are comparatively difficult to handle.
Price
Dry Cell: Dry cells are comparatively expensive.
Wet Cell: Wet cells are less expensive than dry cells.
Manufacture
Dry Cell: Dry cells are comparatively difficult to manufacture.
Wet Cell: Wet cells are easy to manufacture.
Overcharging
Dry Cell: Dry cells cannot withstand overcharging.
Wet Cell: Wet cells has the ability to withstand overcharging.
Conclusion
Wet cells were the first to be made and consist of glass jars filled with solutions. These solutions are corrosive as they mainly contain sulphuric acid. There is a tendency for the liquid to be leaked and cause harm. However, dry cell batteries have solid electrolytes which don’t spill out. Therefore, safety-wise, dry cells are a better choice. Due to the large size of wet cells, they can be only used in larger equipment, e.g. car batteries, and cannot be used in small devices, like mobile phones. Dry cells have a higher energy density compared to wet cells. Therefore, dry cells, which can be made on a smaller scale, are used in comparatively smaller devices. However, dry cells are much more difficult to manufacture than wet cells. This is the difference between dry cell and wet cell.
Reference:
1. “Electric cell.” The Free Dictionary. Farlex, n.d. Web. 21 Feb. 2017.
2. “Electric cell.” The Free Dictionary. Farlex, n.d. Web. 21 Feb. 2017.
3. Hoffman, Sandra. “What is a Dry Cell Battery? Find out!” UPS Battery Center. N.p., 10 Dec. 2014. Web. 21 Feb. 2017.
4. “Definition Wet Cell.” Weird Science Kids. Com. N.p., n.d. Web. 21 Feb. 2017.
5. “Dry Cell Battery – Boundless Open Textbook.” Boundless. N.p., n.d. Web. 21 Feb. 2017.
6. Smith, Brett. “Wet Cell Battery Vs. Dry Cell Battery.” Sciencing.com. Leaf Group Ltd., n.d. Web.
Image Courtesy:
1. “Zinc battery” By Mcy jerry (CC BY 2.5) via Commons Wikimedia
2.”Galvanic cell labelled” By Hazmat2 – Own work (CC BY 3.0) via Commons Wikimedia
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