Primary Connections: Linking science with literacy
© State of Victoria (Department of Education, Employment and Training)

Talking solutions

The terms used to describe solutions and the process of dissolving can sometimes appear quite complex. However, with a little help, there is no reason why they cannot be used correctly and understood. The following is an everyday description (in italics) of a solution being prepared, followed by the technical version with each new term described and explained.

Part 1 - Making a solution
Ten grams of salt was added to one litre of water and stirred. A slight taste of salt could be detected in the water.

Ten grams of the solute (sodium chloride or common salt) was added to one litre of the solvent (water). The solute is the substance being dissolved and is the substance in the lesser quantity by mass. In the case of solids in liquids, the solid is generally considered as the solute and the liquid the solvent.

The water, being in the greater quantity, acts as the solvent. The salt quickly dissolves in the solvent forming a dilute salt water solution. The term "dilute solution" means that a relatively small amount of solute has been dissolved in a lot of solvent. Another way of describing a dilute solution is "a weak solution".

Part 2 - Concentrated and saturated
More salt was added and stirred in until the water tasted very salty and the salt started to pile up on the bottom. From this point onwards, any extra salt added simply fell to the bottom of the container.

As more solute was added, the solution became more concentrated until no more salt could be dissolved. At this stage, the solution was saturated and no more solute could dissolve, no matter how much it was stirred. The term "concentrated" means a relatively large amount of solute is dissolved in the solvent.

As a solute is added to a solvent, the resulting solution starts diluted and becomes more concentrated until no more will dissolve, at which point the solution is said to be saturated with solute.

Part 3 - Heating and cooling
The salt water and extra salt were then heated. Slowly the salt on the bottom of the container started to disappear, eventually disappearing entirely. When allowed to cool, the salt slowly reappeared on the sides and bottom of the container.

Upon heating the saturated solution, with extra undissolved salt on the bottom, the salt began to dissolve because solubility increases with temperature. Eventually all the salt dissolved when the solution was hot enough.

As cooling began, the salt started to recrystallise (as it cooled the solution was losing its ability to hold the solute in solution). Solute crystals again formed on the various surfaces of the container.

"Solubility" describes how much solute can be dissolved and held in each litre of solution. Some substances are more soluble than others; for example, sugar is highly soluble in water, while oxygen gas is only slightly soluble. Generally, solid and liquid solutes are more soluble in hot solvent than cold while, on the other hand, gases are more soluble in cold solvent than hot. Substances which do not dissolve in a solvent are said to be insoluble; for example wax is generally considered insoluble in water.