Question:-
Which indicator is used in the titration of strong acid and weak base?
The options are...
- A. Phenolphthalein
- B. Bromothymol blue
- C. Thymol blue
- D. Methyl orange
The correct answer is D: Methyl orange indicator suitable in the strong acid weak base titration.
Explanation:
The equivalence point for titration of a strong acid and a weak base is less than 07.00; therefore the methyl orange is a suitable chemical indicator that changes sharply at the endpoint.
Methyl orange has a pKa of 3.47, and a pH range of 3.1 to 4.4, it turns red in acidic medium and yellow in basic conditions. At the beginning of this type of titration, the pH is high, so the solution appears yellow.
When acid is added, the solution becomes more acidic, and the methyl orange turns red which is the endpoint of the reaction. When a strong acid reacts to a weak base, pH will change gradually making an acidic solution with a pH of less than 07.00.
This is why an indicator that changes its basic color to an acidic color is an excellent choice for this titration. The titration of hydrochloric acid and ammonia is an example of strong acid and weak base.
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