WHICH OF THE FOLLOWING IS USED AS AN INDICATOR IN THE TITRATION OF A WEAK ACID AND A STRONG BASE?

In the titration of a weak acid and a strong base, phenolphthalein is commonly used as an indicator.

Here's the step-by-step process:

1. The titration process begins with the addition of the weak acid into the titration flask.
2. A few drops of phenolphthalein are added. Initially, the solution will be colorless as phenolphthalein is colorless in acidic solution.
3. The strong base is slowly added from the burette into the flask containing the weak acid and phenolphthalein.
4. As the base is added, it reacts with the acid to form water and a salt. This process is called neutralization.
5. The point at which all the acid has reacted with the base is called the equivalence point. At this point, the solution will still be colorless.
6. If more base is added past the equivalence point, the solution will turn pink. This is because phenolphthalein is pink in basic solution. This point is called the endpoint.
7. The volume of base needed to reach the endpoint is noted and used to calculate the concentration of the acid.

Phenolphthalein is a suitable indicator for this type of titration because its pH range (8.2 to 10.0) falls within the pH change that occurs near the equivalence point of the titration of a weak acid with a strong base.