Question

What occurs at the end of the point when sulphuric acid neutralizes sodium hydroxide solution using phenolphthalein indicator?

Answer 1

The neutralization of Sulphuric acid with sodium hydroxide is a titration reaction. This is an example of an acid-base titration where a strong acid like sulphuric acid is titrated against a strong base like sodium hydroxide. We can take Sulphuric acid as an analyte and sodium hydroxide as a titrant. An indicator is used to indicate the endpoint in the reaction. Phenolphthalein is the indicator in this reaction.

Complete answer:
Phenolphthalein acts as an indicator that makes the titrating solution pink. But during the complete titration, the indicator turns colourless as soon as it is put in the titrating solution. When the reaction reaches the endpoint, the indicator turns pink because the strong acid has completely neutralized the strong base.
During titration, we know the concentration of each substance in the reaction. Sulphuric acid is the analyte present in the flask and sodium hydroxide is present in the burette. The ml of sodium hydroxide is noted to neutralize the given ml of sulphuric acid. The concentration of the titrant is known and the concentration of the analyte has to be found out.
The phenolphthalein turns pink in colour when the solution turns basic. The pH then restores to more neutral, but it depends mostly on the concentration of the analyte of the titrant.

Note:
The endpoint of the pH is dependent on the concentration of the strong acid and strong base. When the colour of the solution changes from colourless to a specific colour it indicates that the analyte is completely titrated. Also, remember the indicator does not affect the pH of the solution.