Question

In base vs Acid titration, at the end pointmethyl orange is present as

• A. quinonoid form
• B. heterocyclic form
• C. phenolic form
• D. benzenoid form

Answer 1

The Correct Option is A

To understand which form of methyl orange is present at the endpoint of a base versus acid titration, we need to understand the nature of methyl orange, which is a pH indicator.

Methyl orange is a common indicator used in titrations because it changes color at a pH of around 3.1 to 4.4. It is red in acidic conditions (pH < 3.1) and yellow in neutral to slightly alkaline conditions (pH > 4.4).

The molecular structure of methyl orange undergoes a transformation at this pH range due to its protonation and deprotonation. The acid form of methyl orange, present in more acidic conditions, exists in its benzenoid form. As the pH increases and the solution becomes less acidic or slightly alkaline, methyl orange transitions to its quinonoid form. The quinonoid form is responsible for the color change observed from red to yellow.

At the endpoint of a titration involving a strong acid and strong base, the pH is typically around 7 for a neutral solution. For an endpoint determination involving a weak base and strong acid, the endpoint can be within the 3.1 - 4.4 range where methyl orange shows a clear color change due to the quinonoid form forming.

Thus, the correct option is that methyl orange is present in its quinonoid form at the endpoint in a typical acid-base titration using methyl orange as the indicator.