WAEC Chemistry 2019 Paper

Concept:Titration of a strong base ($\mathrm{NaOH}$) with a weak acid ($\mathrm{HCOOH}$) requires an indicator that changes colour in the basic pH range.Explanation:At the equivalence point, the solution is basic because the salt $\mathrm{HCOONa}$ undergoes hydrolysis.Therefore, the indicator must have its pH range in alkaline medium.Phenolphthalein changes colour in the pH range $8.3 - 10.0$, which suits a strong base–weak acid titration.Methyl orange and methyl red change colour in acidic medium, while bromocresol is also unsuitable here.Hence, phenolphthalein is the correct choice.Answer:D. phenolphthalein