How Many Types of Indicators

Introduction

There are two types of chemical indicators. They are natural and artificial indicators. There are elements of acidic and basic nature in the earth. Substances with acidic nature have a sour taste and substances with a basic nature have a bitter taste. But substances that are harmful to human beings cannot be distinguished by tasting. Hence, we need chemical indicators to distinguish substances with acidic and basic natures. Indicators change colour when they are exposed to acidic or alkaline solutions in different ways respectively. By observing this colour change, we can identify whether a substance is acidic or basic in nature.

Natural Indicators

Natural indicators are either found naturally occurring or are created from naturally occurring substances. There are many natural indicators used as chemical testers.

1. Litmus paper

Litmus is a very common natural indicator. It is made from dyes produced by naturally occurring lichens. There are two types of litmus paper, red litmus paper and blue litmus paper. If the pH is less than 4.5, the litmus paper is red and when the pH is more than 8.3, the litmus paper is blue.

When an acidic solution is added to the red litmus paper, it does not change colour. In the same way, when an alkaline solution is added to blue litmus paper, it stays the same without a colour change.

But when an alkaline solution is added to red litmus paper, it turns blue and when an acidic solution is added to blue litmus paper, it changes to red. When distilled water is added, litmus paper turns purple. When a solution shows no change in both red and blue litmus papers, it is called a neutral solution.

2. Turmeric

Turmeric is a natural acid-base indicator. When an alkaline solution is added, turmeric turns deep red. When an acidic solution is added, its colour remains unchanged. This explains the reason why turmeric stains turn red when soap is applied.

3. China rose

China rose is found commonly in many houses and gardens. To use it as an indicator, use warm water to soak some of the china rose petals for a few hours. Then, add an acidic or alkaline solution. When an acidic solution is added, its colour turns bright pink or magenta. In case of alkaline contact, the solution turns green.

4. Red cabbage

In red cabbage, there is anthocyanin, a pigment which is water soluble and changes its colour when exposed to an acidic or alkaline medium. Anthocyanin turns red when exposed to an acidic medium and bluish-green in an alkaline medium.

Artificial Indicators

Artificial or synthetic indicators are created in a laboratory environment and are not naturally occurring. They are made from chemicals and can be used as colour-changing indicators. There are two major artificial indicators used for acid-base testing.

1. Methyl Orange

Methyl orange is mainly used in titration as an acid-base indicator. The actual colour of methyl orange is orange. It can only be used to indicate mineral acids and strong bases. When an acidic solution is added, methyl orange turns red while in a basic medium, it turns yellow. Methyl orange cannot be used to indicate weak acids or weak bases.

2. Phenolphthalein

Phenolphthalein is another synthetic indicator. It is water soluble and has a dark purple colour. When in an acidic medium, it turns colourless. In an alkaline medium, phenolphthalein turns light pink in colour.

Conclusion

Acid-base indicators are not only useful for determining the pH of a solution but they can also be used to demonstrate the presence of acids and bases. For example, when an acid-base indicator is added to a solution of hydrochloric acid, the solution will turn the colour associated with acids on the indicator's colour chart. Similarly, when an acid-base indicator is added to a solution of sodium hydroxide, the solution will turn the colour associated with bases on the indicator's colour chart.

In conclusion, acid-base indicators are substances that change colour in the presence of an acid or base. These indicators are commonly used in chemistry experiments to determine the pH of a solution, and can also be used to demonstrate the presence of acids and bases. There are many different acid-base indicators available, each with its own unique range of colours, and they are an important tool for chemists.