Solution

A solution is a homogeneous chemical mixture of two or more substances uniformly combined at a level that cannot be separated by the naked eye or ordinary microscope. This mixture is described as "single-phase" (homogeneous), meaning each part of the solution has the same composition.

Every solution has two basic components: the solvent, the substance present in the greatest amount that dissolves the other, and the solute, the substance being dissolved. A common example is sugar dissolved in water: the water is the solvent and the sugar is the solute.

How solutions form

When a substance is added to a solvent, the molecules or ions of the solvent move around the particles of the substance and then break apart the bonds holding them together. This process is called dissolution. The strength of the interaction between the solvent and the substance determines whether the substance will dissolve or not. For this reason water, which is polar, dissolves sugar and salt well, but dissolves oil poorly.

Concentration (strength of the solution)

Concentration indicates how much dissolved substance is present in a given volume or mass of solvent. It is measured in various ways, such as by percentage or in moles per litre (molarity). A solution with little dissolved substance is called dilute, while one with much is called concentrated.

Saturation limit

Every solvent has a limit to how much substance it can hold at a given temperature. When this limit is reached, the solution is said to be saturated, and additional substance settles out. Increased temperature generally increases the solubility of solid substances in water, while gases dissolve less well as temperature rises.

Types of solutions

Solutions are not only liquids. Gas solutions exist, such as the air we breathe, which is a mixture of nitrogen, oxygen, and other gases. There are also solid solutions, such as alloys (mumusuc) combining metals like copper and tin. Aqueous (liquid) solutions are the most common in chemistry and everyday life.