(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.
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