Question

Phenolphthalein is ________________ type of indicator.
(A) Natural Indicator
(B) Universal Indicator
(C) Synthetic Indicator
(D) None of the above

Answer 1

Hint: Indicators are chemical or biological compounds that are indicative of the end point of a chemical reaction that is in general a chemical reaction. Their solution changes colour due to the changes in the pH of the solution.

Complete Step by Step Answer
The indicators are generally conjugate bases of weak acids or conjugate acids of weak bases. At a particular pH value they change colour due to the formation of the weak acid or base by taking up or giving up hydrogen ions and absorbing a particular wavelength of light and reflecting its complementary colour that we see. Each indicator gives a particular colour within a particular pH range. Phenolphthalein indicator gives a bright pink colour in the pH range of $ 10\text{ }\text{ }12 $ and hence it is used as an acid-base indicator. The first colour transition of phenolphthalein takes place in the pH range below $ 0-8.3 $ when it changes its colour from orange to colourless. In the pH range of $ 8.3-10 $ it changes from colourless to pink and then again in the pH range of $ 12-13 $ it becomes colourless.
Hence, Phenolphthalein is a “synthetic indicator” used for the detection of the titration of acids and bases.
So the correct answer is option C.

Note
A natural indicator is one that is obtained from the extracts of different natural products while a universal indicator is one that is made of solution of different compounds that exhibit several smooth colour changes over a wide range of pH values to indicate the acidity or the alkalinity of the solutions.