This preview shows page 1. Sign up to view the full content.
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
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!
Work in Pairs on this experiment.
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...
View Full Document
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.
- Spring '07