Analytical Chemistry

The question pertains to the titration of magnesium ions with EDTA using Solochrome Black as an indicator. Here, we are required to determine the correct statements regarding the magnesium-EDTA titration in terms of stability, color change, and pH requirements.

1. Magnesium–indicator complex is more stable than the magnesium–EDTA complex: This statement is incorrect. EDTA forms a more stable complex with magnesium as it is a strong chelating agent, allowing the titration to occur effectively with magnesium ions in the presence of the indicator.
2. At the end point, the colour changes from red to blue: This statement is correct. At the beginning of the titration, the magnesium-indicator complex is red. Upon titration with EDTA, magnesium ions complex with EDTA, releasing the indicator, which turns from red to blue, signifying the end point.
3. After the end point, the colour of the solution is due to the indicator: This statement is correct. After all the magnesium has reacted with EDTA, the color of the solution is determined by the indicator itself, which is blue, indicating the completion of the titration.
4. pH range of 7 – 10.5 is necessary for observing the specific colour change: This statement is correct. The specified pH range is critical because both the complexation reaction between magnesium and EDTA and the distinct color change of the indicator are pH-dependent. The indicator is most effective within this pH range, allowing the clear observation of the red-to-blue transition.

Thus, the correct answers are:.

• At the end point, the colour changes from red to blue.
• After the end point, the colour of the solution is due to the indicator.
• pH range of 7 – 10.5 is necessary for observing the specific colour change.