question_answer

(a) Define a universal indicator. 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 and which one of the solutions A and B will have a higher pH value?

(c) Name one salt whose solution has pH more than 7 and one salt whose solution has pH less than 7.

Answer:

(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

(i) an acid solution < 7

(ii) a base solution > 7

(iii) a neutral solution = 7

(c)        (i) The salts of strong acids and weak bases gives acidic solution having pH less than 7. Example,\[N{{H}_{4}}Cl,\] Ammonium Chloride will have pH less than 7.

(ii) The salts of weak acids and strong bases gives basic solution having pH more than 7. Example, \[N{{a}_{2}}C{{O}_{3}}\] Sodium Carbonate will have pH more than 7.