Question

Which of the following is a synthetic indicator?
A.) Phenolphthalein
B.) Litmus
C.) Common salt
D.) Vinegar

Answer 1

Hint: Acid – base indicators prepared from artificial substances are known as synthetic indicators. They are synthesized in laboratories.

Complete step by step answer:
Natural indicators are the acid – base indicators obtained from natural sources. On the other hand, synthetic indicators are exactly their contrary. Synthetic indicators are obtained from artificial substances that are synthesized in laboratories. Some examples of natural indicators are:
Litmus: Litmus solution is a purple dye extracted from lichen, a plant belonging to the division thallophyta. Its colour is red in acidic solution, blue in alkaline solution and purple in neutral solution. A blue litmus paper turns red when it is dipped in acidic solution, it won't change its colour in the basic solution. A red litmus changes into blue when dipped in basic solution and doesn't change colour in acidic solutions.
Turmeric: Turmeric in acidic medium shows no change in colour but in basic medium, its colour changes from yellow to deep red.

Some examples of synthetic indicators are:
Phenolphthalein: Phenolphthalein is a synthetic indicator which is colourless in acidic medium but gives pink colour in basic medium. It is majorly used in acid – base titrations.
Methyl orange: The colour of methyl orange in acidic medium is red and in basic medium, its colour changes to yellow.

While, common salt and vinegar are not used as indicators.

Hence, the correct answer is (A) Phenolphthalein.

Note: In the given options, the only synthetic product given is phenolphthalein. The other compounds are obtained from nature. Hence, there can only be one possible answer.