Types of Solutions

A solution is a homogeneous mixture of two or more components. "Homogeneous" means the composition and every property of the mixture are uniform throughout — wherever you sample it, it looks and behaves the same. When sugar is dissolved in water, there is no separate sugar region and water region to point at; the mixture is uniform right down to the molecular scale.

Solvent and solute

Within a solution, the components are given names based on how much of each is present:

• The solvent is the component present in the largest amount. It fixes the physical state (solid, liquid or gas) in which the solution exists.
• The solute(s) are the remaining component or components — present in a smaller amount than the solvent.

A solution can, in principle, contain many components, but this chapter restricts itself to binary solutions — solutions made of exactly two components — to keep the ideas manageable. In a binary solution, either component can be a solid, a liquid or a gas, which gives nine possible solute–solvent combinations in all, summarised below.

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