Choose the correct representation of conductometric titration of benzoic acid vs sodium hydroxide.

Solution

Chemistry ma’am · 3 steps

Benzoic acid is weak, so start low, dip a little, rise slowly, then shoot up once NaOH is in excess.

1. Weak acid start. Benzoic acid is a weak acid and ionises only slightly. So very few ions are present, and the conductance starts low, not high.

   Stage	What happens	Conductance
   First few drops	Benzoate ions formed push back the acid's ionisation (common ion effect), so the few free H⁺ disappear	dips slightly
   Up to equivalence	Un-ionised acid turns into ions: C₆H₅COOH + NaOH → C₆H₅COO⁻ + Na⁺ + H₂O	rises slowly
   After equivalence	Excess Na⁺ and highly mobile OH⁻ build up	rises steeply

2. Two slopes. Both parts of the graph go up, but the line after the end point is much steeper because OH⁻ conducts far better than benzoate. The kink between the two slopes marks the equivalence point.
3. So. Only graph (c) shows a small initial dip, a gentle rise and then a steep rise, so (c) is the correct representation.

The idea to keep. In conductometric titrations, think about which ions are being removed and which are being added. Weak acid with strong base: low start, slow rise, then a steep rise from excess OH⁻.

Answer from the NTA final answer key. Solution by PrepWiser.