Writing a lab report on Complexion of Metal Ions with EDTA. We initially prepared an EDTA solution with target concentration of 0.05 M, and titrated that solution by NaOH (known concentration). The second "pathway" used to determine exact concentration of EDTA was by adding a MgSO4 7H2O to the EDTA solution and titrating it by the same NaOH. I am trying to figure out what makes the titration curve shift when the metal is added, and basically I am trying to explain/understand why this pathway can be used in order to determine the concentration of the EDTA solution.