An aqueous solution containing 25.0 mL of 0.0800 M ammonia (NH₃, Kb=1.8×10−5 at 25 °C) is titrated with 0.100 M HCl. The chemist considering possible indicators has narrowed the choice to methyl red (pH 4.4–6.2) and phenolphthalein (pH 8.2–10.0).
Assume ideal solution behavior and constant temperature.
(a) Calculate the pH of the solution at the equivalence point of the titration. Show all steps clearly.
(b) Using your result from part (a), select the better indicator for this titration and justify your selection.
(c) For the less-suitable indicator, state whether its use would cause the reported molarity of ammonia to be too high, too low, or essentially unaffected. Support your answer with reasoning based on the direction of titration error.