Question

Choose the CORRECT answer(s) with respect to the magnesium-EDTA titration carried out in the pH range 7 – 10.5, using Solochrome black as indicator

• A. Magnesium–indicator complex is more stable than the magnesium–EDTA complex
• B. At the end point, the colour changes from red to blue
• C. After the end point, the colour of the solution is due to the indicator
• D. pH range of 7 – 10.5 is necessary for observing the specific colour change

Hint:

In magnesium-EDTA titrations, the pH range and the choice of indicator are crucial for observing the proper colour change at the end point.

Answer 1

The Correct Option is B, C, D

Step 1: Understanding the magnesium-EDTA titration.
In the magnesium-EDTA titration, the pH range 7-10.5 is critical for the stability of the magnesium-EDTA complex. The indicator used, Solochrome black, changes colour based on the presence of free magnesium ions. At the end point, the indicator changes colour, but after the end point, the colour of the solution is solely due to the indicator.

Step 2: Analyzing the options.
(A) Magnesium–indicator complex is more stable than the magnesium–EDTA complex: Incorrect — The magnesium-EDTA complex is generally more stable than the magnesium-indicator complex.
(B) At the end point, the colour changes from red to blue: Incorrect — The colour change is not from red to blue at the end point.
(C) After the end point, the colour of the solution is due to the indicator: Correct — This is the correct statement. After the end point, the solution's colour is solely due to the indicator.
(D) pH range of 7 – 10.5 is necessary for observing the specific colour change: Incorrect — While the pH range is important, this statement is not the most accurate.

Step 3: Conclusion.
The correct answer is (C). After the end point, the colour change observed is due to the indicator.