DETERMINATION OF HARDNESS OF AN UNKNOWN SAMPLE Measure 10.0 mL of the sample using a pipet, and place it in an Erlenmeyer flask. Add 40 mL of deionized water, 1 mL of the conc. ammonia solution and one indicator buffer tablet. Swirl the flask gently to mix the contents. You will get a red solution. Titrate the solution against 0.0100 M EDTA solution until the colour changes from red over grey to green. Record the burette readings with 2 decimal places. From the amount of used EDTA solution and given that the molar stoichiometry of the M2+-EDTA complex is 1:1, it is possible to calculate the hardness of the water expressed as parts per million of Ca2+ (mg/l). Perform the titration at least three times and form the average. Discussion Comment on all parts of the experiment (yield of the zeolite synthesis, determination of calcium, treatment of the calcium sample with zeolite, answer all the questions, conclusion)! my question is how is color is change in to red to green. why is color change ?