A great number of chemicals in our environment and even in our homes can be categorized into two groups, acids and bases. Acids and bases can be considered as been opposites. Strong acids or strong bases are very corrosive and cause severe burns to the skin if accidentally splashed. An acid is neutralized by a base and vice versa.

These chemicals have unique properties. Acids taste sour while bases feel slippery.

Some chemicals can change colour when placed in acid or base solutions. The dye from red cabbage is a natural indicator because it changes colour from purple to green when placed in a base solution.

Universal indicator goes through a range of colour changes ranging from pink when placed in a strong acid to purple when placed in a strong base. The range of colours are shown on the right. In a neutral solution, where no base or acid is present, or equal amounts of acid and base are present, the universal indicator is green.

You will notice that each colour has a number. This number indicates the pH of the solution containing the acid or base.