In an aqueous solution containing a mixture of Zn2+and Mg2+, how would

you determine their contents by means of EDTA titration?

To determine the content of Zn2+ and Mg2+ in an aqueous solution using EDTA titration, you would follow these steps:

1. First, prepare the solution for titration by combining a known quantity of the solution containing Zn2+ and Mg2+ with a buffer solution. The buffer helps to maintain a constant pH, which is important for accurate titration.

2. Next, add a few drops of Eriochrome Black T indicator to the solution. The Eriochrome Black T indicator will form a complex with Mg2+, turning the solution from pink to blue. Meanwhile, Zn2+ does not form a colored complex with Eriochrome Black T and remains colorless.

3. Begin titration by slowly adding an EDTA (Ethylene Diamine Tetraacetic Acid) solution from a burette to the solution. EDTA is a chelating agent that complexes with metal ions. Initially, Zn2+ ions will be titrated until all of them react with the EDTA. This is indicated by the disappearance of the colorless Zn2+ complex.

4. Continue the titration by adding the EDTA solution until the pink color changes to a blue color, indicating that all the Mg2+ ions have reacted with the EDTA and formed a complex. At this point, both Zn2+ and Mg2+ have been titrated.

5. Note the volume of EDTA solution used. Since EDTA reacts stoichiometrically with metal ions, the volume of EDTA solution used can be used to calculate the content of Zn2+ and Mg2+ in the original solution.

6. To differentiate between Zn2+ and Mg2+ concentrations, you need to perform a back titration. Add a known excess of EDTA solution to a separate solution containing only Zn2+. This ensures that all Zn2+ ions have formed a complex with EDTA. From there, titrate the excess EDTA with a standard solution of a metal ion that forms a colored complex with EDTA (e.g., Mn2+). Record the volume of the standard solution needed to reach the endpoint.

7. Finally, using the volume of the EDTA solution used in the main titration and the volume of the standard solution used in the back titration, you can calculate the concentrations of Zn2+ and Mg2+ in the original solution using the stoichiometry of the reactions.

It is important to note that proper lab techniques and accurate measurements are crucial for obtaining reliable results in EDTA titration.