Question

Which mixed indicator is used for nitrogen estimation?

• A. Bromophenol blue and thymol blue
• B. Thymol blue and cresol red
• C. Methyl orange and methyl red
• D. Methyl red and bromocresol green

Hint:

When using mixed indicators in titrations, ensure that they cover the entire pH range necessary for detecting the equivalence point, as seen in nitrogen estimation.

Answer 1

The Correct Option is A

In nitrogen estimation, especially using the Kjeldahl method, a mixture of bromophenol blue and thymol blue indicators is used to detect the end point of the titration. These indicators change color as the pH of the solution shifts, indicating when the nitrogen content has been fully reacted with the titrant. Step 1: Role of Bromophenol Blue and Thymol Blue
- Bromophenol blue is effective in the acidic pH range, while thymol blue is used to track changes in a slightly more basic range. The two work together to provide a clear endpoint.

Step 2: Other Indicators
- While other indicators like methyl orange and methyl red can be used in acid-base titrations, they are not as effective in the specific pH ranges required for nitrogen estimation.

Step 3: Conclusion
Thus, the correct mixed indicator for nitrogen estimation is bromophenol blue and thymol blue.