This task serves as an example of metal ion determination using complexometry. Introduction: The con — Organic Chemistry Chemistry Question

This task serves as an example of metal ion determination using complexometry.

Introduction:
The concentration of Ni²⁺ ions can be determined by complexation with EDTA (ethylenediamine tetraacetate). EDTA is a multidentate ligand which forms a 1 : 1 complex with Ni²⁺ ions. The indicator is murexide which also form a complex with Ni²⁺ ions but this complex is less stable than that with EDTA. The aim of this experiment is to determine the amount of crystal water in nickel(II) sulphate.

List of chemical needed:
- hydrate of nickel(II) sulfate, solid, 300 mg
- standard EDTA solution
- murexide, indicator
- ammonium chloride, solid, 3 g
- ammonia solution, concentrated, 20 cm₃
- demineralized water

Procedure:
Hydrate of nickel(II) sulphate (ca. 300 mg) is weighed accurately and dissolved in water. Use a 100 cm₃ volumetric flask. Make a buffer solution by dissolving ammonium chloride (2.7 g) and concentrated ammonia (17.5 cm₃) in water (50 cm₃). Fill the burette with EDTA standard solution (0.01 mol dm^-3). Transfer 10.00 cm₃ of nickel(II) sulphate solution with a pipette into an Erlenmeyer flask (200 cm₃) and dilute it with water (ca. 90 cm₃). Add buffer (10 cm₃) while swirling the Erlenmeyer flask. Add a small amount of solid murexide indicator and ensure its complete dissolution. Titrate with EDTA solution until change of color (yellow to purple). When the change of color is slow, add some concentrated ammonia at the end of the titration. This experiment should be carried out in duplicate.