Substances around us have an acidic as well as basic nature. Acidic substances are the substances which are sour in taste, whereas bases are bitter. By tasting some substances we can differentiate them as acidic or basic substances. But substances which are used in the laboratory can be harmful if tasted. So chemical indicators are needed to identify the nature of substances. Indicators are substances that change colour when they are added to acidic or alkaline solutions. Litmus, phenolphthalein, and methyl orange are all indicators that are commonly used in the laboratory. Change in property is observed when they come in contact with an acidic or basic solution.
Chemical indicators are of two types: artificial and natural indicators.
Litmus, red cabbage, turmeric, and china rose are some naturally occurring indicators around us.
Litmus is the most commonly used natural chemical indicator. It is the solution of different types of dyes naturally obtained from lichens. It shows purple colour in the distilled water. It changes its colour to blue when added to a basic solution and gives a red colour when tested with an acidic solution. It is often found in the form of strips of paper, known as litmus paper. It is found in two colours, red litmus paper and blue litmus paper. Acids change the blue litmus paper to red and the base changes the red litmus paper to blue. Solutions which do not make any difference in the red or blue litmus are known as neutral solutions.
Turmeric which we use in our daily life for the preparation of food can also be used as a chemical indicator. In acidic medium, turmeric appears yellow and in basic medium, it changes its colour to brownish red. This is why turmeric stain becomes red when soap is applied onto it.
China rose (gurhal) can be easily found in one out of five houses. When a solution of china rose is used with a basic solution it changes its colour to green, whereas when used with an acidic solution it changes its colour to bright pink or magenta.
What is an Indicator? What Are Acid-Base Indicators?
This was just a brief layout about the natural indicators around us. To know more about the chemical indicators kindly visit BYJU’S.