Nowadys, indicators have become technologically advanced and can be used for the main purpose of indicating whether something is acidic, basic or neutral. This is possible because in solutions of different pH, the colour of the inidcator will change simultaneously with pH change. This is made possible by pigments in the indicators. Hand made indicators include universal indicator, methyl orange, phenolphthalein and many more.
Acids and bases are diverse in this world. They are everywhere ranging from foods to trees to rocks and many more. Indicators can be used to determine whether these substances are acidic, basic or neutral.
Manufactured indicators are one type and the second type is natural indicators. Believe it or not, the majority of fruits, vegetables and flowers contain pigments which may be used as acid-base indicators. For example, Red cabbage contains within its leaves a red pigment called anthocyanin. This is present in many other vegetables such as capsicum, carrot, tulips and many more. This anthocyanin has the ability to change colour in a variety of pH due to certain chemical reactions that take place involving H+ and OH- ions. Read on to discover the chemistry involved in these reactions.
Anthocyanins are complex molecules that have the ability to add and/or subtract hydroxide (OH-) ions. When anthocyanin is added to acidic solutions, hydroxide (OH-) ions will leave the anthocyanin molecule. On the other hand, when anthocyanin is added to basic solutions, the OH- ions from the water will attach themselves to the anthocyanin molecule.Therefore, anthocyanin is general name given to a series of similar compounds each with a different number of OH- ions attached. Anthocyanin is an indicator for the reason that each form of the compound reacts with light differently so that each form is a different colour
Anthocyanin can be extracted from natural plants and vegetables in many ways. A very common way of extracting anthocyanin form plants is to place the plant in low boiling point alcohols which have been acidified with HCl and boiling for a while.
There are other methods of extracting anthocyanin from vegetables. One very common method is boiling the vegetable in distilled water and waiting till boiling starts. The water reacts with the anthocyanin pigment which allows wxperimenters to use this water as the indicator.
Anthocyanin presents many vegetables such as beets, berries, cherries, fiji apples, eggplant, grapes etc with the red-purplish colour.
Anthocyanin gives colour to plants for a reason. This colour of plants and flowers helps attract pollinating animals to the flowers and aslo animals which help in seed dispersal.