Solute

Figure 1: Example of salt (solute) getting dissolved in water (solvent) to make a salt water solution.

A solute is simply a substance that dissolves in some other substance - known as a solvent - to form a solution. Although a solute is generally thought of as being solid, a solute can be either solid, liquid, or gas. Based on the chemical properties of both the solvent and the solute, the amount of solute that will dissolve in a solvent will vary. The solubility of a solute depends on the temperature, volume and mass ratio, and other chemical properties of the substances.

To learn more about solutes and solutions please see UC Davis' Chem wiki.

CO₂ as a Solute

Figure 2: The process of gaseous carbon dioxide dissolving in oceans and forming bicarbonate and carbonate.

A solute does not have to be a solid, it can be a gas like carbon dioxide (CO₂). Carbon dioxide in the atmosphere is soluble in water (the solvent), which means it can become dissolved CO₂ in the oceans. As seen in figure 2, the dissolved carbon dioxide then undergoes chemical reactions with water to produce carbonic acid (H₂CO₃), bicarbonate (HCO₃^–), carbonate (CO₃^2-) and hydrogen ions (H⁺). Most of the CO₂ dissolving or produced in the ocean is quickly converted to bicarbonate and hydrogen ions.

The more CO₂ is dissolved in the oceans, the more hydrogen ions are produced which consequently lowers the pH of the solution (the ocean in this case). As anthropogenic sources of atmospheric CO₂ have increased, the oceans have been absorbing an increasing amount of carbon dioxide. As a result, there has been a decline in ocean pH and an increase in acidity.

Please see the page about ocean acidification for more information.

Further Reading

• Solvent
• Solid, Liquid
• Chemical reaction
• pH
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