Solution
This article is about a chemical solution; for other uses of the term "solution", see solution (disambiguation)In
chemistry, a
solution is a homogeneous
mixture composed of one or more substances, known as
solutes, dissolved in another substance, known as a
solvent. A common example is a
solid, such as
salt or
sugar, dissolved in
water, a
liquid.
Gases may
dissolve in liquids, for example,
carbon dioxide or
oxygen in water. Liquids may dissolve in other liquids and gases in other gases.
Examples of solid solutions are
alloys and certain
minerals.
An
ideal solution is one where the interactions of the
molecules of the solvent with each other 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.
The solvent is conventionally defined as the substance that exists in a greater quantity than the solute(s) in the solution. If both solute and solvent exist in equal quantities (such as in a 50%
ethanol, 50% water solution), the concepts of "solute" and "solvent" become less relevant, but the substance that is more often used as a solvent is normally designated as the solvent (in this example, water).
Solvents can be broadly classified into
polar and non-polar solvents. A common measure of the polarity of a solvent is the
dielectric constant. The most widely used polar solvent is water, with a dielectric constant of 78.5. Ethanol, with a dielectic constant of 24.3, has intermediate polarity. An example of a non-polar solvent is
hexane, which has a dielectic 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. Then hold this charged rod close to a running stream of the solvent. If the path of the solvent deviates when the rod is held close to it, it is a polar solvent. Certain molecules have polar and non-polar regions, for example
sodium dodecyl sulfate. This class of molecules (called
amphipathic molecules) includes
surfactants like
soaps and
emulsifiers, as they have the ability to stabilize emulsions by aligning themselves on the interface between the non-polar and polar liquids, with their polar ends in the polar liquid and their non-polar ends in the non-polar liquid.
During
solvation, especially when the solvent is polar, a structure forms around it, which 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.
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.
*
Colligative properties*
Colloid*
Molar solution*
Percentage solution*
Solubility equilibrium*
Solubility*
Suspension (chemistry)
