Question

Which of the following plot represents the graph of pH against volume of alkali added in the titration of NaOH and HCl?

• A. Graph A
• B. Graph B
• C. Graph C
• D. Graph D

Hint:

Equivalence point for strong acid-strong base is at pH = 7.

Answer 1

The Correct Option is A

The question asks for the correct graph representing the titration curve of NaOH (a strong base) and HCl (a strong acid). In a titration of a strong acid with a strong base, the pH starts low, increases gradually, and then sharply rises at the equivalence point, before leveling off at a higher pH level.

1. Initial Region: The pH starts low because the solution initially contains only HCl, a strong acid.
2. Buffer Region: As NaOH is added, it reacts with HCl to form water and increases the pH gradually towards neutrality.
3. Equivalence Point: For strong acid-strong base titrations, the equivalence point is at pH 7, where the number of moles of H₃O⁺ equals OH^-.
4. Beyond Equivalence Point: Adding more NaOH will make the solution basic, causing a sharp rise in pH.

Evaluating each graph:

• Graph A: Shows a low starting pH, a gradual increase, a sharp rise at equivalence (pH 7), and levels off high, consistent with a strong acid-strong base titration.
• Graph B, C, D: Do not match the typical strong acid-strong base titration curve. Each has either an incorrect starting pH or change pattern.

The correct graph for the titration of NaOH and HCl is Graph A.