Question

Phenolphthalein of pH range $8-10$ is used in which of the following type of titration as a suitable indicator?

• A. ${NH}_{4}OH$ and $HCl$
• B. ${NH}_{4}OH$ and $HCOOH$
• C. ${NH}_{4}OH$ and $C_2{H}_4{O}_2$
• D. $NaOH$ and $C_2{H}_4{O}_2$

Answer 1

Answer: (D)

$NaOH$ and $C_2{H}_4{O}_2$

If one reagent is a weak acid or base and the other is a strong acid or base, the titration curve is irregular and the pH shifts less with small additions of titrant near the equivalence point. For example, the titration curve for the titration between acetic acid (a weak acid) and sodium hydroxide (a strong base) is pictured. The equivalence point occurs between pH 8-10, indicating the solution is basic at the equivalence point and an indicator such as phenolphthalein would be appropriate.

Hence option D is correct.