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Indicators

Indicators are substances that indicate the presence of an acid or base in a given matter. The presence of acidic or basic or neutral character is indicated by a change in colour that occurs when an indicator is added to the substance whose nature is to be tested. In other words, indicators show different colours in acidic, basic and neutral solutions.

Indicators can be natural or synthetic. Natural indicators are those indicators which can be obtained from nature or natural products. Litmus is a natural dye which is extracted from lichens. It shows red colour in acidic solutions and blue colour in basic solutions. All indicators do not show the same colour change in acids, bases and neutral solutions. Turmeric is an easily accessible natural indicator. When added to acidic solution, it changes the colour of the solution to dark yellow and when added to basic solutions, it changes the colour of the solution to red. The juice obtained by boiling a piece of red cabbage and the extracts of petals of flowers like China rose can also be used as natural indicators.

Synthetic indicators are those indicators which are prepared in laboratories. Examples of synthetic indicators include phenolphthalein, methyl orange etc. Like natural indicators, different synthetic indicators show different colours in acidic, basic and neutral solutions. Phenolphthalein is colourless in acids and pink in bases.