It is important that you appreciate that edta has

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Unformatted text preview: the solution will turn blue. If we have carefully measured the amount of EDTA that we have added, then we can determine the total amount of calcium and/or magnesium in the sample. It is important that you appreciate that EDTA has acid/base properties. It has four acid constants, as is shown below (Note: Y = EDTA4-) Ka1 = 1.0 x 10-2 H4Y H+ + H3YH3Y- H+ + H2Y2-Ka2 = 2.2 x 10-3 H2Y2- H+ + HY3Ka3 = 6.9 x 10-7 HY3- H+ + Y4Ka4 = 5.5 x 10-11 For this reason, analyses must be done at a constant pH and one that will enable the ligand to bind successfully with the metal. These determinations will be conducted at pH 10 via the addition of a NH4OH/NH4Cl (pKa = 9.24) buffer. 24 Safety: 1. The pH 10 buffer is 10 M ammonia. Keep it under the fume hood as much as possible and avoid breathing its vapors. 2. Wear your goggles! PROCEDURE Work in Pairs on this experiment. Pre-Laboratory Preparation During the laboratory period before beginning this experiment (Electrochemical Cells) you were instructed to dry a sample of pure calcium carbonate and an unknown sample. Part I. Preparatio...
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This note was uploaded on 04/09/2013 for the course CHE CHE 2C taught by Professor Nasiri during the Spring '07 term at UC Davis.

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