Question

The best indicator for the detection of endpoint in the titration of a weak acid and a strong base is:
A) Methyl orange (3 to 4)
B) Methyl red (5 to 6)
C) Bromothymol blue (6 to 7.5)
D) Phenolphthalein (8 to 9.6)

Answer 1

Hint: Indicators are the substance which are used to identify the given substance is acid or base by detecting the colour change and ${P^H}$ also used to identify the acid and base.

Complete answer:
Indicator is a substance that usually indicates the colour change in presence of acid and alkali.
Weak acid is a substance which dissociates to a very less extent in water and gives hydronium ion.
Strong base is a substance which dissociates to a high extent in water and gives hydroxyl ion.
Titration is the process of chemical analysis in which the quantity of one of the substances is determined by adding exactly known quantities of another substance.
The end point in the titration indicates that the indicator shows that the exact amount of reactant necessary for a complete reaction has been added to a solution.
The given titration is between weak acid and strong base. So if acid and base reacts gives salt. But here weak acid and strong base reacts and forms basic salt.
The $Ph$ of basic salt is greater than 7.
First option is Methyl orange $Ph$ which ranges from 3 to 4 it indicates acidic salt.
Second option is Methyl red $Ph$ is ranging from 5 to 6, it indicates weak acidic salt.
Third option is Bromothymol blue $Ph$ is ranging from 6 to 7.5 it indicates neutral salt.
Fourth option is Phenolphthalein $Ph$ is ranging from 8 to 9.6 it indicates basic salt.

So, the correct answer is option D.

Note:
The $Ph$ for acidic substance ranges from 1 to 6 and $Ph$ 7 indicates neutral and $Ph$ for basic substance ranges from 8 to 14. The strong acid $Ph$ is 1to 2 and the strong base $Ph$ is 11 to 14.