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A concentration cell has two sections with different concentrations connected by a component. When activated, the concentrations equalize, generating a voltage that can be measured using a voltmeter and the Nernst equation. Corrosion can occur due to metal ions, oxygen concentration, and contact with other materials. Concentration cells can be used to measure soil acidity and analyze chemicals.
A concentration cell is divided into two different sections, which are connected by a component to allow the electron particles to pass through, such as a salt bridge. These two half cells contain electrodes and the solutions in each are different in their concentrations. When the concentration cell is activated, the concentrated solution typically becomes more diluted while the dispersed one adds molecules, until both are equal. Usually when equilibrium is close, a voltage is generated. The strength of this reaction can be measured by calculating the potential of the cell, using a mathematical formula called the Nernst equation.
Calculating the potential of a concentration cell usually requires a voltmeter. The value provided by the meter, which can be either positive or negative, can then be plugged into the equation and used with the concentration level to determine the potential. Electrons flow from one substance to another in a concentration cell. The section that loses particles is called the oxidation side, while the reduction side gains them.
Metal parts are often used in these types of cells and different areas of them can be exposed to different concentrations of material. Some sections of the metal may have a higher electrical potential than others, which can lead to corrosion. While a concentration cell can be cleaned to prevent this from happening, this is often difficult when the system is placed in the ground, for example.
Corrosion can occur due to metal ions. If the cell contains or is exposed to water, is not sealed, or lacks a protective coating, areas near high metal ion levels can corrode. Uneven oxygen concentrations, which can occur on metal surfaces underwater, can lead to corrosion where gas levels are low. Points between adjacent parts and wood, rubber or plastic near a metal surface are usually where degradation occurs. An active-passive concentration cell develops when there is oxygen and a passive film is punctured under a layer of salt, causing pitting in the metal.
Concentration cells are often used as meters to measure the acidity and basicity of soil. These usually have one end exposed to soil and another end held in a potash solution. You can then compare the two measurements. Generally the higher the voltage produced, the more acidic the sample. A concentration cell can also be used to analyze chemicals and test different materials for corrosion susceptibility.
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