question_answer

  To the three solutions listed below, a few drops of phenolphthalein and blue litmus were added separately. Specify the colour change in each case, if any:

Name of the solution	Colour change with phenolphthalein	Colour change with blue litmus
(a) Sodium carbonate
(b) Hydrochloric acid
(c) Sodium chloride

Answer:

                Basic solutions turn red litmus paper blue. The salt of a weak acid and a strong base gives a basic solution. So, the given salt X is the salt of a weak acid and strong base. Example: When sodium carbonate is dissolved in water, it gets hydrolyzed to some extent and forms sodium hydroxide and carbonic acid. Being a strong base, sodium hydroxide is fully ionized and gives a large an hydroxide ions (OH-). Carbonic acid is a weak acid which is only slightly and hence, gives a small amount of hydrogen ions (H+). The H+ ions prod carbonic acid neutralizes only a small amount of OH" ions produced by hydroxide and the rest amount of OH- ions are present in the solution. He Na2CO3 solution is basic in nature. It turns red litmus blue.