Complexometric titration (also known as chelatometry) is a type of volumetric analysis that uses the formation of a colored complex to identify the titration's end point. Complexometric titration is used to determine the hardness. The hardness of water is estimated by titrating it with a standard solution of the complexing agent ethylene diamine tetra acetic acid (EDTA/EBT).
Water hardness is the total calcium and magnesium ion concentration in a water sample expressed as calcium carbonate concentration. Temporary hardness and permanent hardness are the two types of hardness.
Why we use buffer solution in temporary hardness of water:
When estimating the water hardness, an indicator dye is employed that turns the solution pink when Mg2+ and Ca2+ are present in the sample, or blue when all of the metal ions have interacted with the EDTA4-. As we know, the pH must be about 10.00 for the EDTA to release its H+ ions and yield the EDTA4- solution required for the reaction with Ca2+ and Mg2+.
The reaction (EDTA → EDTA4- + 4H+) changes the pH of the entire solution on its own, therefore we keep adding EDTA solution until the solution is blue and all traces of pink have disappeared. As a result, we'll need a buffer that will keep the overall pH of the solution at 10.00 even if we have to add a significant amount of EDTA.
Which buffer added during the determination of the hardness of water?
In EDTA titration, an ammonium hydroxide (NH4OH)-ammonium chloride (NH4Cl) buffer solution of pH 10.00 is used, because it resists the change in pH.
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