Question

(a) Define indicator. Name two indicators obtained from plants.
(b) Write balanced chemical equation for the reaction that takes place when sodium oxide reacts with water. How will this solution behave towards phenolphthalein and red litmus paper ?
(c) State what happen when sodium hydroxide solution reacts with dilute hydrochloric acid. What is this reaction called ?

Answer 1

(a) Indicator is any substance that gives visible sign, usually by colour change, of the presence or absence of a chemical species. They are generally used to check if a given substance is acidic or basic in nature. Two natural indicators are litmus and turmeric.
(b) $N{a}_{2}O+H_{2}O\to 2NaOH$ NaOH in phenolphthalein shows pink colour and turns red litmus blue.
(c) $NaOH+HCl(dil.)\to NaCl+H_{2}O$
This is a neutralisation reaction where an acid and base react to give salt and water.