Question

why does 100 ml of water only rise 5 ml if you add 20 ml of salt

Answer 1

At the molecular level, there is room between water molecules for some of the ions to fill.

Answer 2

If you put more volume of salt in than you see the volume of the solution rise, then you fit more stuff in a smaller space. The amount of mass will be the same, so you must have a denser solution. That is, more mass per not as much space is more density.

So you can assume that a chemical reaction is taking place. So I guess that this would be because there is a chemical reaction that produces denser molecules.

Answer 3

"So you can assume that a chemical reaction is taking place. So I guess that this would be because there is a chemical reaction that produces denser molecules."

I don't think so.