Adam Seabrease
Experiment 6
EDTA Titration of the Hardness of Water
Introduction:
In this experiment, we tested the hardness of local tap water. We used a complexation
titration using ethylenediaminetetraacetic acid (EDTA) as the titrant to determine the amount of
Ca2+ in the water. EDTA was used because EDTA has 1:1 stoichiometric ratio with Ca2+.
Procedure:
A pH meter, NaOH, and HCl were used to create an ammonia buffer with pH of 10. 5
mL of buffer was added to 1 g EDTA and diluted in 250 mL distilled water. In 100 mL HCl, .5
g CaCO3 was dissolved. In an Erlenmeyer flask, 5 mL of buffer and CaCO3 solution and 5 drops
of hydroxynaphthnol blue indicator to standardize the EDTA. The EDTA was standardized
thrice. The standardized EDTA was used to titrate 100 mL of tap water, 5 mL ammonia buffer
and 5 drops of hydroxynaphthnol blue indicator three times. Three titrations were done using
EDTA as the titrant, and 10 mL portions of antacid solution with 5 mL ammonia buffer and 5
drops of hydroxynaphthnol blue indicator. The antacid solution was made by dissolving an
Tums antacid tablet in 100 mL 0.1M HCl.
Data:
EDTA mass: 1.0007 g
CaCO3 mass: 0.5007 g
Buffer pH: 10.08
Tums antacid mass: 1.2665 g
Supposed Ca2+ in antacid: .400 g
Titration
Standardization
Tap Water
Antacid
mL Used in Titration
1
21.03
4.28
16.13
mL Used in Titration
2
21.12
4.01
16.61
mL Used in Titration
3
21.52
3.98
16.26
Calculations:
Concentration of EDTA:
Titration 1
0.0119M
Titration 2
0.0118M
Titration 3
0.0116M
Average
0.0118±0.0001M
Titration 2
4.7266x10-4
Titration 3
4.6913x10-4
Average
4.8209x10-4±1.9476x10-4
Titration 2
0.0078±0.0001
Titration 3
0.0077±0.0001
Sum
0.0231±0.0002
Concentration Ca2+ in tap water:
Titration 1
5.0449x10-4
Ppm of Ca2+ in tap water:
Mass of Ca2+ in Tums:
Titration 1
0.0076±0.0001
Weight Percent of Ca2+ in Antacid:
Conclusion:
We found there is very little Ca2+ in the local York tap water. We found that there is only 19.32
ppm. Also, we found there is not as much Ca2+ in a Tums antacid as the label says. This may be
due to the loss of antacid in the mortar and pestle when the tablet was crushed.