Question

Explain why the indicator bromocresol green would not have been an appropriate choice as an indicator for the titration of aqueous HCl with aqueous NaOH

Answer 1

An acid base indicator is a substane which can show different colours in different medium that is in acidic and basic medium during the course of reaction.The change in colour should be sharp, stable and easily distinguishable.

Every indicator has its own pH range where it shows the colour changes.the suitable working range of indicator lies between

The choie of indicator for a partiular acid base titration depends on nature of acid and base involved in the titration.

the reaction between HCl and NaOH being a strong acid vs strong base is efficiently analysed by phenolpthalien (with pH range of 8 to 9.8) and shows distinguishing colours of pink(in alkaline medium) to colourless(in acid medium).other indicators include methyl orange and methyl red.

But Bromocresol green with pH range of 3.8 to 4.6 with colour changes Blue(in alkaline medium ) to yellow(in acid medium) cannot show sharp colour changes in strong accid vs strong base titrations as the pH range is different.