EDTA Titration of the Hardness of Water
Introduction
The tap water of the lab and an antacid will be analyzed for the concentration of calcium. They
will be analyzed by titration and by pH.
Procedure
-Calibrate the pH meter with ammonia buffer (pH=10)
-Make 0.01M EDTA solution
-0.9306g EDTA dissolved in 5mL of buffer in a 250mL volumetric flask
-Make CaCl2 solution
-0.5g CaCO3 in 100mL volumetric flask and dilute to line with 0.1M HCl
-Standardize EDTA Solution
-3mL CaCl2 solution, 5mL buffer, 5 drops of indicator in 250mL Erlenmeyer
-Titrate with EDTA solution and repeat for three good trials
-Hardness of Water
-50mL tap water, 3mL buffer, 5 drops of indicator in 250mL Erlenmeyer
-Titrate with EDTA solution and repeat for three good trials
-Analysis of Antacid
-Weight antacid tablet and place in 100mL volumetric flask
-Dissolve in 5mL of buffer
-Dilute to line with 0.1M HCl
-5mL of antacid solution, 3mL buffer, and 5 drops of indicator into 250mL Erlenmeyer
flask
-Titrate with EDTA solution and repeat for three good trials
Data
CaCO3: 0.5034g initial
Solid EDTA: 0.9779g initial
Standardize EDTA Solution
Trial 1
Trial 2
Trial 3
Average
Amount of EDTA Titrated (mL)
12.44
11.84
11.52
11.93
Trial 1
Trial 2
Trial 3
Average
Amount of EDTA Titrated (mL)
4.58
4.29
4.28
4.38
Hardness of Water
Analysis of Antacid
Weight of Whole Tablet: 1.3316
Weight of Crushed tablet: 1.3002g
Amount of EDTA Titrated (mL)
1.50
2.11
3.50
2.76
2.47
Trial 1
Trial 2
Trial 3
Trial 4
Average
Calculations
M of EDTA Solution
0.9779𝑔 ×
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴
= 0.002627𝑚𝑜𝑙
372.24𝑔
0.002627𝑚𝑜𝑙
= 0.011𝑀
0.250𝐿
M of CaCl2 Solution
0.5034𝑔 ×
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑙2
×
= 0.002515𝑚𝑜𝑙 𝐶𝑎𝐶𝑙2
100.087𝑔
2 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3
0.002515𝑚𝑜𝑙
= 0.025𝑀
0.1𝐿
Concentration of Ca2+
0.00438𝐿 × 0.011𝑀 𝐸𝐷𝑇𝐴 = 0.000048𝑚𝑜𝑙 𝐸𝐷𝑇𝐴
0.000048𝑚𝑜𝑙 𝐸𝐷𝑇𝐴 ×
1 𝑚𝑜𝑙 𝐶𝑎2+
1
×
= 0.00096𝑀 𝐶𝑎2+
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴 0.05𝐿
Hardness of Water
0.00096𝑀 ×
40.078𝑔
= 0.038475𝑔
1𝑚𝑜𝑙
0.038475𝑔 1000𝑚𝑔 38.47𝑚𝑔
×
=
1𝐿
1𝑔
𝐿
%Ca2+ per Tablet Claimed
500mg Ca2+ per tablet
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3
1 𝑚𝑜𝑙 𝐶𝑎2+
40.087𝑔
0.500𝑔 𝐶𝑎𝐶𝑂3 ×
×
×
= 0.200261𝑔 𝐶𝑎2+
100.087𝑔
1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 𝐶𝑎2+
0.200261𝑔
× 100% = 15.04% 𝐶𝑎2+
1.3316𝑔
%Ca2+ Actually Present
Average: 2.47mL titrated
0.00247𝐿 × 0.011𝑀 = 0.000027𝑚𝑜𝑙 𝐸𝐷𝑇𝐴
0.000027𝑚𝑜𝑙 ×
1 𝑚𝑜𝑙 𝐶𝑎2+ 40.087𝑔 𝐶𝑎2+
×
= 0.001082𝑔 𝐶𝑎2+
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴
1 𝑚𝑜𝑙 𝐶𝑎2+
0.001082𝑔 × 20 𝑝𝑎𝑟𝑡𝑠 𝑝𝑒𝑟 𝑡𝑎𝑏𝑙𝑒𝑡𝑠 𝑖𝑛 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 = 0.02164𝑔
0.02164𝑔
× 100% = 1.63%
1.3316𝑔
Conclusion
The data shows that the hardness of water from the lab tap is 38.47mg/L. Then in comparison of
the weight percent calcium per tablet is much larger than the weight percent calculated. 15.4% vs.
1.63%. A source of error is that the Tums solution made was not fully dissolved which could have
affected the amount of EDTA needed to view a color change and throw off the results.