A certain indicator (an organic dye) has . For which of the following titrations may it be suitable? — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

An indicator with $pK_a = 5$ has a colour transition interval roughly between pH 4 and 6. This indicator is suitable for titrations whose steep pH drop at the equivalence point passes through this acidic range. The titration of a strong acid with a weak base, or the complete neutralization of a weak dibasic salt like $\text{Na}_2\text{CO}_3$ with HCl (the second equivalence point occurs near pH 4), fits this criteria perfectly (Option C). The other options describe titrations producing alkaline equivalence points. Therefore, correct answer is C.