Solute, solvent and solution

Three words for a single mixture

When you dissolve sugar in water, you get a solution. This solution consists of two parts: the solute, the substance that is dissolved (in this case, sugar), and the solvent, the liquid that dissolves it (in this case, water). The solvent is almost always present in much greater quantities than the solute.

The most common solvent: water

When the solvent is water, we refer to it as an aqueous solution. This is the case for the vast majority of solutions studied in A-level chemistry: salt water (solute: NaCl), sugar water (solute: sucrose), water with a few drops of acid added, etc.

A solution is homogeneous

A true solution is homogeneous: on a macroscopic scale, the solute can no longer be distinguished from the solvent; the mixture looks the same throughout. This is what distinguishes it from a simple suspension (such as sand in water), where the particles remain visible and eventually settle out.

Practical example

To prepare 100 mL of salt water, for example, 2 g of salt (NaCl, the solute) is dissolved in water (the solvent) until a total volume of 100 mL of solution is obtained. It is important to remember that the final volume is that of the SOLUTION, not just that of the water added.

Common mistake

A frequent misconception is to believe that the volume of the solution is simply the sum of the volume of the solvent and the volume (or mass) of the solute added. In reality, we always make up to a given final volume (using a volumetric flask, for example), this final volume being that of the solution, and not simply the sum of the individual volumes.