EDTA – An Introduction
CHM 103
Sinex
EDTA is ethylenediaminetetraacetic aicd
Six binding sites
4 H on carboxylic
acid groups (H’s are
removed, so –COO-)
2 lone pairs of
electrons on
nitrogens
EDTA Chime structure
For more information on EDTA – see the MOTM for March 2004.
Fe+3 + EDTA-4  FeEDTA-1
1:1 metal ion to EDTA
metal ion with octahedral geometry
chemistry
• Ca+2 with EDTA – 1:1
• at equivalence point:
moles Ca = moles EDTA
• so to find moles: moles = M x VL
• standard calcium solution from CaCO3
CaCO3(s) + 2HCl(aq) CaCl2(aq) + CO2(g) + H2O
• indicator – MgIn-
wine red
HIn-2
sky blue
After Ca+2 reacts with EDTA, EDTA complexes Mg+2 from indicator.
Tracking the metal ion - EDTA titration
indicator
If a student masses out 0.5251 g calcium carbonate,
dissolves it in HCl, and then places it into a 500.0 mL
volumetric flask, what is the molarity of the calcium ion?
0.5251 g x 1 mole/100g = 5.251 x 10-3 moles Ca+2
5.251 x 10-3 moles Ca+2/0.5000L = 0.1050 M
answer
If 25.00 mL of the Ca+2 solution above requires 18.93 mL
of EDTA to titrate, what is the molarity of the EDTA?
MCa x VCa = MEDTA x VEDTA
hint