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Lab VI Determination of Water Hardness by EDTA Titration Olivia Lott Group 12 Purpose : Students will use EDTA titration to measure the total concentration of Ca 2+ and Mg 2+ in water and determine water hardness of a 15 mL unknown and report if the unknown is “hard” or “soft” water. Materials : 4 mM Mg 2+ solution, M EDTA titrant solution, NH 3 /NH 4 + , pH 10 buffer, calmagite indicator, 2400 ppm CaCO 3 stock solution, pipet, 100 mL volumetric flask, Erlenmeyer flasks beakers, buret, pH paper Procedure : 1. Preparing a working standard solution of 600 ppm CaCO 3 a. Prepare by pipetting 25 mL of 2400 ppm CaCO 3 solution into a 100 mL volumetric flask. Dilute to the mark with distilled water and mix well. 2. Performing a blank correction a. Add approximately 25 mL of distilled water into an Erlenmeyer flask. b. Pipet exactly 2 mL of 4 mM Mg 2+ solution, add 12 drops of calmagite indicator, and add enough NH 3 /NH 4 + until the pH of the solution is about 10 (approximate via pH paper).

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