There are chemicals that change colour at different pH values. These are called indicators . One of the most famous is Litmus . Oxides Oxides are compounds containing Oxygen. Oxides can be Acidic, Basic or Neutral.
Acidic Oxides react with water to form an acid.
NO and NO 2 . Basic Oxides react with water to form an alkali. Most metal oxides are basic. Amazon COM Amazon Co UK Organic Chemistry is a good book for the undergraduate. Visit Amazon by clicking on a logo below.