In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent. The solvent does the dissolving.
Types of solutions
Usually, the substance present in a greatest amount is considered the solvent. Solvents can be gases, liquids, or solids. The solution has the same physical state as the solvent.
If the solvent is a gas, only gases are dissolved under all given set of conditions. An example for a gaseous solution is air (oxygen and other gases dissolved in nitrogen). Since interactions between molecules play almost no role, dilute gases form rather trivial solutions. In part of the literature, they are not even classified as solutions, but addressed as mixtures.
If the solvent is a liquid, then gases, liquids, and solids can be dissolved. Examples are:
- Gas in liquid:
- Oxygen in water.
- Carbon dioxide in water is a less simple example, because the solution is accompanied by a chemical reaction (formation of ions). Note also that the visible bubbles in carbonated water are not the dissolved gas, but only an effervescence; the dissolved gas itself is not visible since it is dissolved on a molecular level.
- Liquid in liquid:
- The mixing of two or more substances of the same chemistry but different concentrations to form a constant.(Homogenization of solutions)
- Alcoholic beverages are basically solutions of ethanol in water.
- Petroleum is a solution of various hydrocarbons.
- Solid in liquid:
Counterexamples are provided by liquid mixtures that are not homogeneous: colloids, suspensions, emulsions are not considered solutions.
Body fluids are examples for complex liquid solutions, containing many different solutes. They are electrolytes since they contain solute ions (e.g. potassium and sodium). Furthermore, they contain solute molecules like sugar and urea. Oxygen and carbon dioxide are also essential components of blood chemistry, where significant changes in their concentrations can be a sign of illness or injury.
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