Question

Assertion: In the acid -base titration involving a strong base and a weak acid, methyl orange can be used as an indicator.
Reason: Methyl orange changes its colour in pH range 3 to 5.
A) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B) Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C) Assertion is correct but Reason is incorrect.
D) Both Assertion and Reason are incorrect.

Answer 1

Hint: Methyl orange is a pH indicator which is used in titrations. It shows a clear and distinct color variance at different pH values. It is orange in colour, hence the name methyl orange.

Complete step by step answer:
Methyl orange is used in acid-base titrations because of its clear and distinct variance of color at different pH values.

-It shows red colour in acidic medium and yellow color in basic medium. Methyl orange changes its color at $p{K}_{a}$ of a mid strength acid and due to this it is used usually in acidic titrations.

-For methyl orange to indicate the pH, the solution should be at least slightly acidic in nature. And therefore, in an acid-base titration of a weak acid and a strong base, methyl orange cannot be used as an indicator.

-Also, methyl orange turns red below pH 3.3 and turns yellow above pH 4.4. Thus, it nullifies the reason provided that it changes its color in the pH range 3 to 5. Therefore, the reason is incorrect.

Hence, the correct answer is option (d).

Note: Methyl orange is toxic when it is ingested. It may cause gastrointestinal irritation with nausea, vomiting and diarrhea. It may also cause respiratory tract irritation.