Acidic, neutral and alkaline

When salt dissolves in water, we cannot see it any more, but it is still there. How can we find out? We let the water evaporate. Put salt water in a shallow dish in a sunny spot. The water slowly leaves as invisible vapour, but the salt cannot become vapour here, so white crystals stay in the dish. This is true for other dissolved solids too, such as sugar or baking soda. A dissolved gas behaves differently. Sparkling water has carbon dioxide dissolved in it. If a bottle stays open, bubbles escape into the air and the water goes flat. When a liquid with only a dissolved gas evaporates, nothing is left in the dish, because the gas has already left. So a dish with white powder tells us a solid was dissolved. An empty dish tells us a gas, or nothing, was dissolved. We do this only in the sun, never on a stove, and a grown-up helps.