Acid-base indicators are weak acids and set up an equilibrium with water as foll

Question

Acid-base indicators are weak acids and set up an equilibrium with water as follows: Hln(aq) + H_2O(l) rightleftarrows H_3O^+(aq) + In^-(aq) Which statement is/are true about acid-base indicators? Indicators change color at pH 7. Indicators change color when all of the Hln has been converted to In^-. Indicators change color when the concentration of Hln = the concentration of In^-. A single indicator, such as phenolphthalein, will tell you the exact pH of a solution. All of the above statements are true.

Explanation / Answer

Ans C. Indicators change colour when the concentration of HIn = concentration of In-

pH = pka when [HIn] = [In-]

so there is equal amounts of acid and the base in solution . When these 2 forms have equal concentration the colour of the indicators is most noticeable.

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