Question

What is general criteria of choosing a suitable indicator for a given titration?

• A. The inidcator should have a broad pH range.
• B. pH at the end point of titration should be close to neutral point of indicator
• C. The indicator should have neutral point at pH =7.
• D. The indicator must show a sharp colour change near the equivalence point of titration point

Answer 1

Answer: (B), (D)

The correct options are
B pH at the end point of titration should be close to neutral point of indicator
D The indicator must show a sharp colour change near the equivalence point of titration point

An acid & base indicator is a substance which changes its colour within limits with variation in pH of the solution to which it is added. Indicators, in general, are either organic weak acids or weak bases with characteristics of having different colours in the ionized and unionized form e.g. phenolphthalein is

a weak acid (the ionized form is the pink and unionized form is colourless).

An indicator is appropriate for a given titration if the rapid change of $pH$ at equivalence overlaps the $pH$ range of the indicator.