Question

Explain why buffer is used during the estimation of total hardness with EDTA and not during the estimation of calcium only hardness

Answer 1

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A few drops of an indicator are added to a water sample. Then, a compound called EDTA (short for ethylenediaminetetraacetic acid) is slowly added to the sample. EDTA forms complexes with the calcium and magnesium ions that are red. Because of the presence of the indicator, when all of the metal ions have formed complexes with the EDTA, the solution will change color from red to blue. If you know how much EDTA you have added and the stoichiometry of the chemical reaction, you can calculate how many metal ions were initially present in the water sample.