JAMB - Chemistry (2025 - No. 93)
The most suitable indicator to be used when reacting ethanedioic acid with potassium hydroxide is
phenolphthalein
methyl orange
methyl red
methyl purple
Açıklama
The reaction involves ethanedioic acid (a weak acid, also known as oxalic acid) and potassium hydroxide (a strong base, KOH).
The titration of a weak acid with a strong base results in an equivalence point at a pH greater than 7 (in the alkaline range). Phenolphthalein is the most suitable indicator for this type of titration because its colour change range (pH 8.3-10.0) falls within the steep, alkaline portion of the titration curve. It changes from colourless in acid to pink in alkaline solution, which provides a sharp and distinct endpoint.