Presented By: Jared Poist and Monique Gray
Hard Water
Hard water is a detectable amount of dissolved cations in
water.
Drinking hard water poses no known health risk.
It causes water to taste bad.
One of the main problems with hard water is it leaves
behind residues and precipitants on a majority of
surfaces.
EDTA
Ethylenediaminetetracetic Acid
This chemical compound forms 1:1 metal complexes
with the majority of the metal cations.
EDTA plays a strong role as a metal-binding agent in
industrial processes, products/supplies such as
cleaning agents and food additives that prevent metalcatalyzed oxidation of food.
Biochemistry Application
EDTA is used in biochemistry to stop enzymatic activity
by binding with the divalent cations from the active
site of enzymes, thus, preventing it from functioning.
Common divalent cations are Ca2+ and Mg2+.
EDTA Continued
EDTA is a mutlidentate ligand or a chelating ligand
The chelate effect is the ability of multidentate ligands
to form more stable metal complexes than those
formed by similar monodentate ligands.
The more electrons pairs an atom has available for
binding the more stable the complex will be.
Compleximetric Titrations
Basically, titrations that are based upon forming metalcation complexes with different ligands.
EDTA Acid-Base Titration
Water sample Information
Deer Park Spring Water
Filtered Water (from Jared’s home refrigerator )
Tap Water Data (came from previous lab experiment)
Introduction to Our Experiment
Plan: use the EDTA titration technique to find
the hardness of water for filtered water and spring
water.
Hypothesis:
(1) The hardness in tap water should be higher than both
filtered water and spring water.
(2) The hardness in filtered water should be higher than
spring water
Procedure: Standardizing EDTA
Prepared Solutions:
0.1 CaCl2 solution and 0.01 EDTA Solution
Added 3mL of CaCl2 into a 250mL flask, 5mL ammonia
buffer (pH 10), and 5 drops of calmagite indicator
Standardized EDTA and recorded 3 good trials
Standardizing EDTA Results
Trial #
EDTA Added (mL)
Molarity of EDTA
1
15.20 mL
0.01973 M
2
14.0 mL
0.02140 M
3
15.0 mL
0.02000 M
Average Molarity:
0.0204 M
Procedure Continued
(1) Calibrated a pH meter with standard solutions, and
used the pH meter to make a buffer with pH 10.
(2) Added 3mL ammonia buffer, 25mL water (sample),
and 5 drops indicator.
(3) Three good trials for each water sample.
Calculations
 mL CaCl2 added x 0.100 Ca2+ M / 1000 mL x 1mol
EDTA/ 1 mol Ca2+ x 1 / L EDTA added = Molarity of
EDTA
 L of EDTA x Average Molarity x 1 mol Ca2+/1 mol
EDTA x 1/ 0.025L = concentration of hardness
 Ca2+ Molarity x grams Ca2+/ 1 mol x 1000mg/1g = ppm
EDTA Titration Results
Trial #
Spring Water
Amount EDTA Added
mL
1
25mL
1.20 mL
2
25mL
1.20 mL
3
25mL
1.10 mL
Trial #
Filtered water
Amount EDTA Added
mL
1
25 mL
1.9 mL
2
25 mL
1.7 mL
3
25mL
2.01 mL
EDTA Titration Results
Trial # 1
Amount Tap Water mL
Amount EDTA Added
mL
1
25 mL
2.68 mL
2
25 mL
2.31 mL
3
25 mL
2.25 mL
Hardness of Water Samples Results
Spring Water
Trial #
Ca2+ Molarity
ppm
1
0.0009792
39.244
2
0.0009792
39.244
3
0.0008976
35.974
Filtered Water
Trial #
Ca2+ Molarity
ppm
1
0.0015504
62.1370
2
0.00138720
55.5970
3
0.00164016
65.7343
Hardness of Water Sample Results
Tap Water
Trial
Ca2+ Molarity
ppm
1
0.00236
94.584
2
0.00203
81.358
3
0.00198
79.354
Conclusion
We found that our first hypothesis was correct, which
stated that tap water had a greater hardness than
spring and filtered water.
We found that our second hypothesis was true, which
stated that filtered water would have a higher hardness
than spring water.