Question

What are indicators? Name any two natural and two synthetic indicators.

Answer 1

Hint: As name suggests indicator will be something which will indicate some change. It could indicate some physical change or some chemical change. Physical changes affect the form of chemical substance but not its chemical composition whereas chemical change occurs when a substance combines with another to form a new substance.

Complete step by step solution:
Indicators are the substances which show a change in color when brought in contact with acids and bases. Indicator that is used most commonly is litmus which is extracted from lichens and is available either in the form of solution or in the form of paper strips known as litmus paper. Natural indicator is a substance which is found naturally and can determine whether the substance is acidic or basic. Some examples of natural indicators are turmeric, grape juice, red cabbage, cherries, onion, beetroot etc. Synthetic indicators are indicators which are synthesized in the laboratory. Examples of synthetic indicators include phenolphthalein, methyl orange etc. litmus paper is also an example of synthetic indicator.

Additional information: Turmeric is yellow in acid and neutral solution but it changes to bright red with bases. Acids turn blue litmus paper to red and bases turn blue litmus paper to red. Methyl orange shows red color in acidic medium and yellow color in basic medium and phenolphthalein turns colorless in acidic solution and pink in basic solution. This is how indicators tell whether the substance is acidic or basic.

Note: Always remember how the color of different indicators change in acidic and basic medium. Indicators detect presence of ${H^ + }$ or $O{H^ - }$ ions in solution. They do so by reacting with these ions. There are many red and blue flowers which contain some pigments that can act as indicators.