Sand is insoluble in water – it does not dissolve in water, no matter how much you heat it or stir it. However, salt and sugar are soluble in water – they dissolve in water to make solutions.

Solute and solvent

A solute is the substance that dissolves to make a solution. In salt solution, salt is the solute. A solvent is the substance that does the dissolving – it dissolves the solute. In salt solution, water is the solvent.

During dissolving, particles of solvent collide with particles of solute. They surround the particles of solute, gradually moving them away until the particles are evenly spread through the solvent.

For each solute and solvent, there is a limit to the mass of solute that will dissolve in a particular volume of the solvent. When no more solute will dissolve, we say that the solution is a saturated solution.

Copper sulfate solution becoming darker blue as more of it dissolves.Copper sulfate solution becomes saturated when no more of the compound will dissolve in the solution

Conservation of mass

The solute does not cease to exist when it dissolves. If the water in the solution is evaporated, the solute is left behind. The total mass stays the same during dissolving. For example, if 1 g of salt is dissolved in 100 g of water, the mass of salt solution formed is 101 g (1 + 100). This is called conservation of mass.