This document provides instructions for determining the concentration of magnesium (Mg) in an unknown sample by titrating with ethylenediaminetetraacetic acid (EDTA). The EDTA solution is standardized against a zinc standard solution. Magnesium in the unknown sample forms a complex with Eriochrome Black T indicator, changing color. When all the magnesium has been chelated by EDTA, the indicator changes to a clear blue, signaling the titration endpoint. Students will titrate the unknown sample with standardized EDTA and calculate the percentage of magnesium in the prepared unknown sample diluted to 100 mL.