Question

If the equivalence point is at a pH of 8.4 in acid-base titration, then ---------- indicator should be used.
A. methyl violet
B. alizarin yellow
C. phenolphthalein
D. methyl red

Answer 1

Hint: Titration is the process of chemical analysis in which the quantity of some constituent of a sample is determined by adding to the measured sample an exactly known quantity of another substance with which the desired constituent reacts in a definite, known proportion. Titrations are mainly classified into 4 types such as acid-base, redox, precipitation and complexometric titrations. Here the question deals with acid-base titrations.

Complete step by step answer:
Here, we have given that in acid base titration the equivalence point is at a pH of 8.4.For each specific pH range we have to use specific indicators. Follow the table given below
Indicator.

Indicator	Color on acidic side	Color on basic side	Range of pH
Methyl violet	Yellow	Violet	0.0-1.6
Bromophenol blue	Yellow	Blue	3.0-4.6
Methyl orange	Red	Yellow	3.1-4.4
Methyl red	Red	Yellow	4.4-6.3
Litmus	Red	Blue	5.0-8.0
Bromothymol blue	Yellow	Blue	6.0-7.6
Phenolphthalein	Colorless	Pink	8.3-10.0
Alizarin yellow	Yellow	Red	10.1-12.0

In the given that the equivalence pH is at 8.4.By analyzing that table we get that Phenolphthalein is used for this acid-base titration.

Hence, the correct option is C.

Note:
Acid–base titrations depend on the neutralization between an acid and a base when mixed in solution. In addition to the sample, an appropriate pH indicator is added to the titration chamber, representing the pH range of the equivalence point. The acid–base indicator indicates the endpoint of the titration by changing color. The endpoint and the equivalence point are not exactly the same because the equivalence point is determined by the stoichiometry of the reaction while the endpoint is just the color change from the indicator. Thus, a careful selection of the indicator will reduce the indicator error.