Dissolving and solutions · Grade 6
When sugar is stirred into water it seems to vanish, but it is still there: it has dissolved. The sugar is the solute, the water is the solvent, and together they make a solution. Substances that dissolve are soluble; substances that don’t, like sand, are insoluble.
Key facts
- Solute + solvent → solution. Sugar (the solute) dissolves in water (the solvent) to make sugar solution.
- Soluble substances dissolve (salt, sugar, instant coffee). Insoluble substances don’t (sand, chalk, oil in water).
- Mass is conserved: the mass of a solution = the mass of the solute + the mass of the solvent.
- Stirring, heating and crushing the solute into smaller pieces all make it dissolve faster.
- A saturated solution can’t dissolve any more solute at that temperature. Solubility is how many grams dissolve in 100 g of water; for most solids it rises with temperature.
- Dissolving is reversible: evaporate the water and the solid is left behind.
- Concentration (g/dm³) = mass of solute (g) ÷ volume of solution (dm³).