In this titration, 25 cm3 of 0.100 mol dm-3 monoprotic acid is in the conical flask and sodium hydroxide solution is added from the burette. Name a suitable indicator. Explain why it is suitable.

Answer 1

Let HA be the monoprotic acid. The neutralization reaction is...

HA + NaOH ==> NaA + H2O

Depending on whether or not the monoprotic acid is a strong or weak acid, different indicators would be used.

If it is a strong acid, neutralization will occur at pH = 7 and a reasonable indicator would be bromthymol blue.

If it is a weak acid, neutralization will occur at pH > 7 and a reasonable indicator would be phenol red or phenolphthalein.

The reason for suitability is based on the pH range in which the indicator changes color.