Question

(a) Define a universal indicated . Mention its one use.
(b) Solution A gives pink colour when a drop of phenolphthalein indicator is added to it. Solution B gives red colour when a drop of methyl orange is added to it. What type of solutions are A and B which one of the solutions A and B will have a higher pH value ?
(c) Name one salt whose solutions has pH more than 7 and one salt whose solution has pH less than 7.

Answer 1

(a) Universal indicator is a mixture of many different indicators which gives different colours at different pH values of the entire pH scale.
It shows different colours at different concentrations of hydrogen ions in a solution.
(b) Solution A gives pink colour when a drop of phenolphthalein indicator is added, therefore A is a base.
Solution B gives red colour when a drop of methyl orange is added to it, therefore B is an acid.
Hence, solution A will have less concentration of hydrogen ion than B.
Thus, A will have pH more than 7 because pH value of :
-an acid solution `lt 7` ,
-a base solution `gt 7` , and
- a neutral solution =7
(c) - The salts of strong acids and weak bases give acidic solution have pH less than 7. Example, `NH_(4)Cl`, Ammonium Chloride will have pH less than 7.
-The salts of a weak , acids and strong bases give basic solution having pH more than 7. Examples, `Na_(2)CO_(3)`, Sodium Carbonate will have pH more than 7.