Drug Problem and Solutions

This article is about a chemical solution; for other uses of the term "solution", see solution (disambiguation)

Dissolving table salt in water

In chemistry, a solution is a homogeneous mixture of one or more substances (the solutes) dissolved in another substance (the solvent). A common example would be a solid dissolving into a liquid, like salt or sugar dissolving in water (or even gold into mercury, forming an amalgam); but also gases may dissolve into liquids, like carbon dioxide or oxygen in water, and liquids and gases into themselves.

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 case, 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.

When a solute is dissolved into a solvent, especially polar solvents, a structure forms around it (a process called solvation), 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 (such as 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 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.

There are several ways to measure the strength of a solution; see concentration for more information.

There are many types of solutions:

References

Streitwieser, Andrew, Heathcock, Clayton H., Kosower, Edward M. (1992). Introduction to Organic Chemistry, 4th ed., Macmillan Publishing Company, New York. ISBN: 0-02-418170-6.

See also

• Colligative properties
• Colloid
• Making up solutions
• Molar solution
• Percentage solution
• Solubility equilibrium
• Solubility
• Suspension (chemistry)