Monique A. Gray
Experiment 6
Quantitative Analytical Chemistry
Experiment 6: EDTA Titration of the Hardness of Water
Introduction
The purpose of this experiment is to practice designing experiments using knowledge obtained from previous
works. Also, use the EDTA titration techniques to find the concentration of the divalent cations Ca 2+ and Mg2+.
Procedure
-
Calibrate the pH Meter with an Ammonia buffer. (Add HCl or NaOH to make the pH of the solution equal
to 10.
Prepare a 0.01M EDTA solution
Prepare a 0.1M CaCl2 solution
Mix 5mL ammonia buffer, 5 drops of calmigite indicator, and 3ml of CaCl2 solution in a 250mL Erlenmeyer
flask
Standardize the EDTA Solution: Titrate the CaCl2 solution with EDTA solution to end point and complete
two more additional trials.
Mix 25mL tap water and indicator into a 250mL flask and titrate with EDTA Solution until endpoint.
Repeat last step for two more additional trials.
Prepare Antacid Solution
Mix with ammonia buffer, and indicator in 250mL flask
Repeat with two more additional trials.
Data
Mass of EDTA: 0.9316g
Mass of CaCO3: 0.051
Mass of Antacid Tablet: 2.5567g
Preparing a Solution of 0.01M EDTA
372.240𝑔 0.01𝑀 0.250𝐿
𝑥
𝑥
= 0.9306𝑔
1 𝑚𝑜𝑙
1𝐿
1
Preparing a Solution of 0.1M CaCl2
0.1𝑀 𝐶𝑎𝐶𝑙2 0.100𝐿 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 100.09𝑔𝐶𝑎𝐶𝑂3
𝑥
𝑥
𝑥
= 1.009𝑔𝐶𝑎𝐶𝑂3
1
1
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑙2
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3
Standardizing EDTA with CaCl2
Trial #
1
2
3
Average Molarity: 0.02203M EDTA
Amount of EDTA Added (mL)
13.95 mL
13.15 mL
13.70 mL
Molarity of Solution
0.0215M
0.0228M
0.0218M
Monique A. Gray
Experiment 6
Find the Molarity of EDTA
3𝑚𝐿 CaCl2 0.100 𝐶𝑎2 + 1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴
1
𝑥
𝑥
𝑥
= 0.0215𝑀
1
1000 𝑚𝐿
1 𝑚𝑜𝑙 𝐶𝑎 2 + 0.01395 𝐿
Tap Water Data
Trial #
1
2
3
Average Molarity: 0.002M
Amount EDTA Added (mL)
2.68 mL
2.31 mL
2.25 mL
Molarity of Ca2+
0.00236M
0.00203M
0.00198M
Finding the Calcium ion Molarity
0.00268𝐿
0.02203𝑀 1 𝑚𝑜𝑙 Ca2 +
1
𝑥
𝑥
𝑥
= 0.00236𝑀
1
1
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴 0.025𝐿
Finding the ppm Concentration
0.00236𝑀 Ca2 + 40.078𝑔 1000𝑚𝑔
𝑥
𝑥
= 94.584 𝑝𝑝𝑚
1
1 𝑚𝑜𝑙
1𝑔
Antacid Tablet Data
Trial #
1
2
3
Average grams of Ca2+: 0.4271g
Amount EDTA Added (mL)
24.1 mL
24.21 mL
24.25mL
Grams Ca2+
0.4256g
0.4275g
0.4282g
Grams claimed by manufacturer
0.051𝑔 𝐶𝑎𝐶𝑂3
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3
1 𝑚𝑜𝑙
40.078𝑔
𝑥
𝑥
𝑥
= 0.0204𝑔
1
100.09𝑔 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 Ca2 +
0.0204𝑔
𝑥 100 = 79.7%
2.5567𝑔
Experimental Calculated Grams of Calcium Ion
0.02410𝐿 0.02203𝑀 1 𝑚𝑜𝑙 𝑐𝑎2 + 40.078𝑔 Ca2 + 20 𝑝𝑎𝑟𝑡𝑠
𝑥
𝑥
𝑥
𝑥
= 0.4256
1
1
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴
1 𝑚𝑜𝑙 Ca2 +
𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
Amount of Calcium in tablet
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑔𝑟𝑎𝑚𝑠 𝐶𝑎𝑙𝑐𝑖𝑢𝑚
𝑥 100
𝑡𝑜𝑡𝑎𝑙 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑡𝑎𝑏𝑙𝑒𝑡
Monique A. Gray
Experiment 6
0.4271𝑔
𝑥 100 = 16.705%
2.5567𝑔
Conclusion
We found that our experiment showed that there was less calcium ion in the antacid tablet than what the
manufacturer claimed. There might have been error associated with calculating the grams and overall percent for
calcium ion for the manufacturer’s claimed value, thus, this could have hindered our results.
We found that the hardness of water was significantly high in the tap water analyzed. The handling of the water
could have contributed to the hardness. Letting water sit without flowing could have resulted in a mineral build up,
which could have made water harder. Also, the type of pipes water flowed through could have contributed to the
hardness because some ions come off more readily in water than others. Lastly, we could have been using city
water and city water may not be as well maintained as compared to other areas.