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Lab 6: Determination of Water Hardness by EDTA Titration Dianie FontenelleTeam Members: Gina Whitten and Nelcy IbarraGroup #76 April, 2017
Purpose: Using an EDTA titration, students will measure the total concentration of Ca2+ and Mg2+ in water and determine the water hardness of a 15 mL unknown; reporting if the unknown is either “hard” or “soft.”Materials:4mM Mg̴̴2+solution0.01 M EDTA titration solution̴̴NH3/NH4+, pH 10 bufferCalmagite indicator2400ppm CaCO3Stock solutionPipet100mL volumetric flaskErlenmeyer flasksBeakersBuretpH paperStirring rod Distilled waterProcedures:1.Prepare a working standard solution of 600 ppm CaCO3a.Prepare by pipetting 25mL of the 2400ppm solution into a 100mL volumetric flask. Dilute solution to the mark with distilled water and mix well. 2.Performing a blank concentrationa.Add approximately 25 mL of distilled water into an Erlenmeyer flask.b.Pipet exactly 2mL of 4 mM Mg2+solution, add 12 drops of the calmagite indicator, and add enough NH3/NH4+ until the pH of the solution is about 10 (test for a pH approximation of 10 using pH paper).