David Millard
Naomi Bryner (partner)
Experiment 6: EDTA Titration of the Hardness of Water
Purpose:
The main objective of this lab is to determine the amount of calcium ion (Ca 2+) that is in tap
water. Ethylenediaminetetraacetic acid (EDTA) will be standardized and used in titrations to
find the hardness of water. An antacid tablet will also be tested to determine the amount of
calcium carbonate that it contains. A procedure will be student made for this experiment.
Procedure:
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Calibrate a pH meter, and then use it to test an ammonia buffer.
Treat the ammonia with NaOH or HCl until it has a pH of 10.
Prepare an EDTA solution using 0.93g of EDTA and 4mL of ammonia diluted to 250mL
with distilled water.
A calcium carbonate (CaCO3) solution was prepared with 0.50g CaCO3 and 100 mL of
0.1M HCl.
Use the CaCO3 solution to standardize the EDTA solution by adding 3mL of CaCO3 and
5mL of ammonia buffer to an erlenmeyer flask along with a calmagite indicator and
titrate with the EDTA solution.
o Repeat titration until three good samples are obtained.
Use the standard EDTA to titrate tap water with an unknown amount of Ca 2+ using 55mL
of tap water and 3mL of ammonia with calmagite indicator.
o Repeat titration until three good samples are obtained.
Mass an antacid tablet, then crush it and add it to a volumetric flask with 5mL of
ammonia buffer and dilute to 100mL with 0.1M HCl.
5mL of the antacid solution with 2mL of the ammonia buffer and the calmagite indicator
were titrated with the EDTA.
o Repeat titration until three good samples are obtained.
Data:
Ammonia pH = 10.10
Crushed antacid tablet = 1.2636g
EDTA = 0.9406g
CaCO3 = 0.5103g
Standardization of EDTA
CaCo3 (mL)
3.00
3.00
3.00
Sample 1
Sample 2
Sample 3
Average
Ammonia (mL)
5.00
5.00
5.00
EDTA (mL)
14.40
14.80
14.70
14.63
Molarity EDTA
0.0106
0.0103
0.0104
0.0105
Titration of tap water
Sample 1
Sample 2
Sample 3
Average
Ammonia
(mL)
3.00
3.00
3.00
Tap water
(mL)
55.00
55.00
55.00
EDTA (mL)
Molarity Ca2+
5.20
5.30
5.20
5.23
0.00099
0.00101
0.00099
0.00099
ppm of Ca2+
39.61
40.37
39.61
39.87
Titration of antacid tablet
Sample 1
Sample 2
Sample 3
Average
Antacid
solution (mL)
5.00
5.00
5.00
Ammonia
(mL)
2.00
2.00
2.00
EDTA (mL)
Ca2+ (g)
10.01
12.29
7.80
10.03
0.084
0.103
0.065
0.084
Percent of
Ca2+ in tablet
6.64%
8.15%
5.17%
6.65%
Calculations:
Finding mass of EDTA needed
molecular mass EDTA disodium ∗
mol EDTA
∗ L = g EDTA
L
Example
372.24g Na2 EDTA ∗
0.010 mol
∗ 0.25L = 0.9306g EDTA needed
1L
Finding grams of CaCO3 needed
M CaCl2 *L CaCl2 *
mol CaCO3 molecular mass CaCO3
*
=g CaCO3 needed
mol CaCl2
mol CaCO3
Example
0.1M CaCl2 *0.100L CaCl2 *
1mol CaCO3 100.09g CaCO3
*
=1.00g CaCO3 needed
1mol CaCl2
1mol CaCO3
Molarity of EDTA
g CaCO3 ∗
mol CaCO3
mol
1
∗
∗ L CaCO3 ∗
= M EDTA
molecular mass CaCO3
L
L EDTA
Example
0.5103g CaCO3 ∗
1mol CaCO3
0.0051mol
1
∗
∗ 0.003L CaCO3 ∗
100.09g CaCO3
0.1L
0.0140L EDTA
= 0.0127M EDTA
[Ca2+] in tap water
mol Ca2+
1
L EDTA ∗ M EDTA ∗
∗
= M Ca2+
2+
mol EDTA L Ca
Example
1mol Ca2+
1
0.00520L EDTA ∗ 0.0105M EDTA ∗
∗
= 0.00099M Ca2+
1mol EDTA 0.055L Ca2+
Hardness of Water
M Ca2+ ∗
g Ca2+
mg
∗
= ppm Ca2+
2+
mol Ca
g
Example
0.00099M Ca2+ ∗
40.078g Ca2+ 1000mg
∗
= 39.68ppm Ca2+
1mol Ca2+
1g
Grams of Ca2+ in sample
mol Ca2+ molecular mass Ca2+
parts
L EDTA ∗ M EDTA ∗
∗
∗
= g Ca2+
mol EDTA
mol Ca2+
solution
Example
0.01001L EDTA ∗ 0.0105M EDTA ∗
1mol Ca2+ 40.078g Ca2+ 20parts
∗
∗
= 0.084g Ca2+
1mol EDTA
1mol Ca2+
solution
Percent Ca2+ in sample
g Ca2+
∗ 100 = %Ca2+ in sample
mass tablet
Example
0.084g Ca2+
∗ 100 = 6.64%
1.2636g
Manufactures listing of Ca2+ in tablet
g CaCO3 ∗
mol CaCO3
mol Ca2+ molecular mass Ca2+
∗
∗
= g Ca2+
molecular mass CaCO3 mol CaCO3
mol Ca2+
Example
0.500g CaCO3 ∗
1mol CaCO3
1mol Ca2+ 40.078g Ca2+
∗
∗
= 0.200g Ca2+
100.09g CaCO3 1mol CaCO3
1mol Ca2+
Percent Ca2+ in tablet
g Ca2+
∗ 100 = %Ca2+ in tablet
mass tablet
Example
0.200g Ca2+
∗ 100 = 15.8% Ca2+ in tablet
1.2636g
Conclusion:
There were two objectives with this lab, first of which was to determine the hardness of tap
water. With our data, it was determined the amount of calcium ion (Ca2+) was on average
39.87ppm. The second objective of this lab was to determine the actual amount of Ca2+ in an
antacid. Based on our calculations, the manufacturer’s antacid tablet contains 15.8% Ca2+. Our
results showed on average the percentage of Ca2+ was 6.65%. this is a difference of almost 10%,
but the amount of Ca2+ is very slight in the tablet so if any small amount is not included in the
transfer from the crushing, it makes a significant impact in the calculations. Also, the titration
for the antacid wasn’t as defined as the previous titrations. The original color returned after a
certain amount of time so there was no definitive end point. The way we determined the end
point was to count thirty seconds, if the color returned before thirty seconds more titrant was
added, if it did not return, the amount of titrant used was recorded.