If you dissolve something in water and the water changes colour, is this a physical or chemical change?
Actully a rather interesting question: it is slightly underspecified. The colour change isnt actually the water changing colour: water itself is (almost) colourless. Some substances (cobalt chloride is one) will change colour in the presence of water when in their crystaline state (not too sure about when you actually dissolve it in water). This is due to water molecules taking part in the crystaline structure, changing its optical properties, this is a chemical change. Other coloured salts are coloured because certain metal ions are strongly coloured (eg. iron (II) is red, and copper (II) is green/blue). When you dissolve these salts in water, the metal ions and the anions seperate, because they form weak bonds with the polar water molecules. It is still the metal ions giving the colour of the solution though, but the separtation of the anions and cations is a (usually) weak chemical reaction. If you however put a non soluble couloured substance in water and it forms a suspension, giv
