Evidence for particles - dilution

A solution is made when a solute, usually a soluble solid compound, is dissolved into a liquid called a solvent, typically water.

If the solute is white (eg sodium chloride) then the solution is colourless. This is because the individual particles (in this case, ions) in the sodium chloride crystals break apart and spread out through the water.

If the solute is coloured (eg blue copper sulfate) then the solution will have a colour. As with the white solute, the particles are now too small to see, and evenly spread out.

Adding more water to copper sulfate solution will make it a paler shade of blue, because the blue particles will now be further apart. This shows that both the solute and solvent are made from tiny particles.