What happens when substances dissolve in water
When you stir sugar into water, the sugar seems to disappear. It has dissolved, forming a solution. The substance that dissolves, sugar, is the solute, and the liquid it dissolves in, water, is the solvent. Water is called the universal solvent because it dissolves so many substances. A solution with a little solute is dilute, and one with a lot of solute is concentrated.
There is a limit to how much solute can dissolve in a fixed amount of water. When no more solute can dissolve at that temperature, the solution is saturated; before that point it is unsaturated. Heating usually allows more of a solid to dissolve, so warm water dissolves more sugar than cold water. Stirring and crushing the solute into smaller pieces make it dissolve faster but do not change the limit. Gases such as oxygen and carbon dioxide also dissolve in water, but less at higher temperatures, which is why a cold soft drink stays fizzy longer.
Why it matters
Solutions are everywhere: sherbet, tea, medicines, oral rehydration solution and the sea itself. Fish depend on oxygen dissolved in water, which is why warm polluted water harms them. Knowing how to make saturated solutions helps grow crystals of salt or sugar. These ideas lead to concentration and mixtures in later classes.
Key terms
- Solute
- The substance that dissolves in a solvent to form a solution.
- Solvent
- The liquid in which a solute dissolves.
- Saturated solution
- A solution in which no more solute can dissolve at a given temperature.
- Solubility
- The maximum amount of a substance that can dissolve in a fixed amount of solvent at a given temperature.