PHENOLPHTHALEIN

During the neutralisation of an acid by a base, the end point refers to the completion of reaction. The detection of end point in acid-base neutralisation is usually made by an acid-base indicator. An acid-base indicator is itself a weak acid (Phenolphthalein) or a weak base (Methyl orange). At 50% ionisation which depends on the medium. the anion furnished by an indicator (acid) cation furnished colour to solution at end point. For example, phenolphthalein dissociation underset("Colourless")(HIn)toH^(+)+underset("Pink")(In^(-)),K_(HIn)=([H^(+)][In^(-)])/([HIn]) is favoured in presence of alkali and pink colour of phenolphthalein ion is noticed as soon as the medium changes to alkali nature. The end point of acid-base neutralisation not necessarily coincides with eqivalence point but it is closer to equivalence point. Also at equivalence point of acid-base neutralisation, pH is not necessarily equal to 7. Which of the following statements are correct? (P) Phenolphthalein is not a good indicator for weak alkali titrations. (Q) Phenolphthalein does not give pink colour with weak alkalies as NH_(4)OH (R) Phenolphthalein is an basic indicator and imparts colour in basic medium.