Difference between revisions of "Solution (chemistry)" - New World Encyclopedia
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[[Image:SaltInWaterSolutionLiquid.jpg|thumb|Dissolving table salt in water.]] | [[Image:SaltInWaterSolutionLiquid.jpg|thumb|Dissolving table salt in water.]] | ||
| − | In [[chemistry]], a '''solution''' is a [[homogeneous]] [[mixture]] | + | In [[chemistry]], a '''solution''' is a combination of two or more substances to form a [[homogeneous]]* [[mixture]]*. The medium that dissolves the other substances is called the '''solvent'''; the substances that become dissolved are called '''solutes'''. The materials mixed together can be in the solid, liquid, or gaseous states. |
| − | + | [[Water]] is a common solvent that can dissolve many other substances. Thus a solution is produced when a solid such as table salt or sugar is dissolved in water. Also, gases such as [[carbon dioxide]] and [[oxygen]] can be dissolved in water. In addition, liquids may dissolve in other liquids, and gases in other gases. [[Alloy]]s are examples of solid solutions. | |
| + | |||
| + | If the solute and solvent exist in equal quantities, such as a 50:50 mixture of [[ethanol]] and water, the concepts of "solute" and "solvent" become less relevant. In such a case, the substance that is more often used as a solvent may be designated as the solvent—in this example, it would be water. | ||
==Ideal solutions== | ==Ideal solutions== | ||
| − | |||
| − | + | An '''ideal solution''' is defined as one in which the interactions of the [[molecule]]s of the solvent with one another are equal to their interactions with the solutes. The properties of an ideal solution can be calculated by the [[linear combination]]* of the properties of its components. | |
| − | |||
==Solvents== | ==Solvents== | ||
| − | Solvents can be broadly classified into [[polar molecule|polar]] and | + | |
| + | Solvents can be broadly classified into [[polar molecule|polar]] and nonpolar solvents. A common measure of the polarity of a solvent is its "[[dielectric constant]]*." Water, a highly polar solvent, has a dielectric constant of 78.5. Ethanol, with a dielectric constant of 24.3, has intermediate polarity. An example of a non-polar solvent is [[hexane]]*, which has a dielectric constant of 1.9. Generally, polar or ionic compounds will only dissolve in polar solvents. | ||
| + | |||
| + | A simple test for the polarity of a liquid solvent is to rub a [[plastic]] rod, to induce [[static electricity]]*. If this charged rod is held close to a running stream of the solvent and the solvent's path deviates, the solvent is polar. | ||
| + | |||
| + | The molecules of some substances, such as [[sodium dodecyl sulfate]]*, have polar and nonpolar regions. This class of molecules (called ''[[amphipathic]]*'' molecules) includes [[surfactant]]*s like [[soap]]s and [[Emulsion#Emulsifier|emulsifier]]s. The molecules of the surfactant can stabilize emulsions by aligning themselves at the interface between the polar and nonpolar liquids, with their polar ends in the polar liquid and their nonpolar ends in the nonpolar liquid. | ||
==Solvation== | ==Solvation== | ||
| − | + | ||
| + | Within a solution, molecules or ions of the solute become surrounded by solvent molecules. If the solvent molecules form relatively stable structures around the solute molecules, this process is known as '''[[solvation]]*'''. For example, when table salt (sodium chloride) is dissolved in water, the polar water molecules surround each of the sodium ions (cations) and chloride ions (anions) to form relatively stable structures. Thus solvation allows the solute-solvent interaction to remain stable. | ||
When no more of a solute can be dissolved into a solvent, the solution is said to be [[Saturation (chemistry)|saturated]]. However, the point at which a solution can become saturated changes significantly with different environmental factors, such as [[temperature]], [[pressure]], and contamination. Raising the [[solubility]] (for example by increasing the temperature) to dissolve more solute, and then lowering the solubility causes a solution to become [[supersaturated]]. | When no more of a solute can be dissolved into a solvent, the solution is said to be [[Saturation (chemistry)|saturated]]. However, the point at which a solution can become saturated changes significantly with different environmental factors, such as [[temperature]], [[pressure]], and contamination. Raising the [[solubility]] (for example by increasing the temperature) to dissolve more solute, and then lowering the solubility causes a solution to become [[supersaturated]]. | ||
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==Concentration== | ==Concentration== | ||
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There are several ways to measure the strength of a solution; see [[concentration]] for more information. [[Total dissolved solids]] is a common term in a range of disciplines, and can have different meanings depending on the analytical method used. In water quality, it refers to the amount of residue remaining after evaporation of water from a sample. | There are several ways to measure the strength of a solution; see [[concentration]] for more information. [[Total dissolved solids]] is a common term in a range of disciplines, and can have different meanings depending on the analytical method used. In water quality, it refers to the amount of residue remaining after evaporation of water from a sample. | ||
Revision as of 06:44, 21 November 2006
In chemistry, a solution is a combination of two or more substances to form a homogeneous mixture. The medium that dissolves the other substances is called the solvent; the substances that become dissolved are called solutes. The materials mixed together can be in the solid, liquid, or gaseous states.
Water is a common solvent that can dissolve many other substances. Thus a solution is produced when a solid such as table salt or sugar is dissolved in water. Also, gases such as carbon dioxide and oxygen can be dissolved in water. In addition, liquids may dissolve in other liquids, and gases in other gases. Alloys are examples of solid solutions.
If the solute and solvent exist in equal quantities, such as a 50:50 mixture of ethanol and water, the concepts of "solute" and "solvent" become less relevant. In such a case, the substance that is more often used as a solvent may be designated as the solvent—in this example, it would be water.
Ideal solutions
An ideal solution is defined as one in which the interactions of the molecules of the solvent with one another are equal to their interactions with the solutes. The properties of an ideal solution can be calculated by the linear combination of the properties of its components.
Solvents
Solvents can be broadly classified into polar and nonpolar solvents. A common measure of the polarity of a solvent is its "dielectric constant." Water, a highly polar solvent, has a dielectric constant of 78.5. Ethanol, with a dielectric constant of 24.3, has intermediate polarity. An example of a non-polar solvent is hexane, which has a dielectric constant of 1.9. Generally, polar or ionic compounds will only dissolve in polar solvents.
A simple test for the polarity of a liquid solvent is to rub a plastic rod, to induce static electricity. If this charged rod is held close to a running stream of the solvent and the solvent's path deviates, the solvent is polar.
The molecules of some substances, such as sodium dodecyl sulfate, have polar and nonpolar regions. This class of molecules (called amphipathic molecules) includes surfactants like soaps and emulsifiers. The molecules of the surfactant can stabilize emulsions by aligning themselves at the interface between the polar and nonpolar liquids, with their polar ends in the polar liquid and their nonpolar ends in the nonpolar liquid.
Solvation
Within a solution, molecules or ions of the solute become surrounded by solvent molecules. If the solvent molecules form relatively stable structures around the solute molecules, this process is known as solvation. For example, when table salt (sodium chloride) is dissolved in water, the polar water molecules surround each of the sodium ions (cations) and chloride ions (anions) to form relatively stable structures. Thus solvation allows the solute-solvent interaction to remain stable.
When no more of a solute can be dissolved into a solvent, the solution is said to be saturated. However, the point at which a solution can become saturated changes significantly with different environmental factors, such as temperature, pressure, and contamination. Raising the solubility (for example by increasing the temperature) to dissolve more solute, and then lowering the solubility causes a solution to become supersaturated.
In general the greater the temperature of a solvent, the more of a given solid solute it can dissolve. However, some compounds exhibit reverse solubility, which means that as a solvent gets warmer, less solute can be dissolved. Some surfactants exhibit this behaviour. The solubility of liquids in liquids is generally less temperature-sensitive than that of solids or gases, while gases usually become less soluble with increasing temperature.
Concentration
There are several ways to measure the strength of a solution; see concentration for more information. Total dissolved solids is a common term in a range of disciplines, and can have different meanings depending on the analytical method used. In water quality, it refers to the amount of residue remaining after evaporation of water from a sample.
Types of solutions
| Examples of solutions | Solute | |||
|---|---|---|---|---|
| Gas | Liquid | Solid | ||
| Solvent | Gas | Oxygen and other gases in nitrogen (air) | Water vapor in air (humidity) | The odor of a solid results from molecules of that solid being dissolved in the air |
| Liquid | Carbon dioxide in water (carbonated water) | Ethanol (common alcohol) in water; various hydrocarbons in each other (petroleum) | Sucrose (table sugar) in water; sodium chloride (table salt) in water; gold in mercury, forming an amalgam | |
| Solid | Hydrogen dissolves rather well in metals; platinum has been studied as a storage medium | Water in activated charcoal; moisture in wood | Steel, duralumin, other metal alloys | |
See also
- Colligative properties
- Colloid
- Molar solution
- Percentage solution
- Solubility equilibrium
- Solubility
- Suspension (chemistry)
- Solution (problem)
ReferencesISBN links support NWE through referral fees
Streitwieser, Andrew and Heathcock, Clayton H., Kosower, Edward M. (1992). Introduction to Organic Chemistry, 4th ed., Macmillan Publishing Company, New York. ISBN 0-02-418170-6.
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