The MSDS HyperGlossary: Solution

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Solubility

Glossary Index

Solvent

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Solution

Definition

A solution is a homogeneous mixture of two or more substances. The substance that is present in the largest amount is called the solvent and the one present in the smaller amount is called a solute.

There can only be one solvent in a solution, but there can be many solutes. Soda pop is a good example - the solvent is water and the solutes include carbon dioxide, sugar, flavorings, caramel color etc.

Additional Info

Solutions can be solids, liquids or gases. The final state of the solution under a given set of conditions depends on the materials and their physical and chemical properties. Some examples include:

Component 1	Component 2	Solution	Examples
Solid	Solid	Solid	Brass (a mixture of ~70% copper and ~30% zinc), "silver" dental fillings (a solid 8:1 mixture of tin and mercury)
Solid	Liquid	Liquid	Sugar dissolved in water, salt water.
Solid	Gas	Solid	Hydrogen gas adsorbed to palladium metal
Liquid	Gas	Liquid	Carbon dioxide dissolved in water (soda water)
Liquid	Liquid	Liquid	Alcohol in water, antifreeze (ethylene glycol in water), gasoline (a complex mixture of hydrocarbons)
Gas	Gas	Gas	Air, natural gas (mostly methane and ethane), synthesis gas (a mixture of hydrogen and carbon monoxide).

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A solution that has some solid present is not a solution, but a heterogeneous mixture.

Solutions fall into three general classes:

Unsaturated solutions have the capacity to dissolve more of the solute.
Saturated solutions have dissolved the maximum amount of solute possible at a given temperature. This is defines the solubility of the solute in the solvent.
Supersaturated solutions contain more solute than is present in a saturated solution.

That last item sounds suspicious - how can something hold more material than it can hold? This is best illustrated by example:

We know that hot water dissolves more sugar than cold water. When we cool a saturated solution of hot sugar water, the water can no longer keep all of the sugar dissolved. Some sugar must crystallize from the solution. However, crystallization requires a nucleation site such as another sugar crystal or a speck of lint for the crystal to grow. If our container is scrupulously clean, the crystals have no place to begin growth! But if we add a crystal of sugar to the supersaturated solution, the "extra" sugar will rapidly drop of out this metastable solution until the solution is again saturated. There are some great general chemistry demos of this principle; see Further Reading below.

When a solid deposits from a solution the process is called crystallization if the solid is crystalline and precipitation if the solid is a powder or amorphous material. The solid that is formed is called the precipitate and the liquid solution that remains is called the supernatant or "mother liquor".

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SDS Relevance

Safety Data Sheets are required to report the physical and chemical characteristics of the material in Section 9 (physical and chemical properties) and that includes the solubility (if known). In addition, SDS's may discuss the properties, stability, or hazards of solutions. "Solution" can also appear in Section 4 (first-aid measures) (for example, saline solutions) or in Section 6 (accidental release measures) procedures (for example, "use a solution of XX and YY to...").