How to choose an indicator for an acid base titration?

An acid-base titration is an experimental technique used to acquire information about a solution containing an acid or base. The acid-base indicator is usually an organic compound that is itself a weak acid or weak base similar to the compounds that give colour to flowers.

Process of titration

In the actual process, a known volume of the acid is taken in a conical flask. Two to four drops of an acid-base indicator are added, then alkali solution of unknown strength is added dropwise from a burette in the acid solution. At the equivalence point, a sharp colour change indicates a neutralization point.

Indicators used

The commonly used acid-base indicators are

  • Phenolphthalein – Colourless /(acid) and pink (alkali)
  • Methyl orange – Pink (acid) and yellow (alkali)

Any indicator with a range between pH 11 and pH 3 may be used. The titration curves for other combinations of strong/weak acid/base pairs offer a more limited change in pH.

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