1. What are indicators? What are the different types of indicators?
An indicator is a dye which changes colour when put into an acid or a base. The different kinds of indicators are-
Natural indicators- Litmus is a natural indicator, litmus solution is a purple dye which is extracted from a plant called lichen. Litmus turns red in acidic solutions and blue in basic solutions. Other examples are turmeric which contains a yellow dye, and red cabbage extract which is red in colour.
Synthetic indicators- These include Methyl orange and phenolphthalein. The neutral colour of methyl orange is orange , in acid solutions it turns red and in basic solutions it turns yellow. The neutral colour of phenolphthalein is colourless, in acidic solution it is colourless and in basic solutions it is pink.
Olfactory indicators- Those substances whose smell changes in acidic or basic solutions are called olfactory indicators, like onion and vanilla extract. Onion has a characteristic smell. When a basic solution like sodium hydroxide is added To a cloth strip treated with onions then the smell cannot be detected, however an acidic solution does not destroy the smell of onion. Vanilla extract has a characteristic pleasant smell. If a basic solution like sodium hydroxide is added to it we cannot detect the characteristic smell of vanilla extract an acidic solution however does not destroy the smell of vanilla extract.
2. What are organic acids and mineral acids?
Organic acids- They are acids which are present in plant material and animals. Organic acids are naturally occurring acids. Some examples are acetic acid in