Quant expt 6

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Naomi Bryner
Experiment 6: EDTA Titration of the Hardness of Water
Purpose: The purpose of this experiment is to design an experiment that will test the hardness of a tap
water sample. This will be found by volumetric analysis via titration with EDTA. Data will be evaluated
using weight percent and ppm of the tap water.
Procedure:
A pH meter was calibrated and used to test an ammonia buffer. The ammonia was treated with NaOH
until a pH of 10 was obtained. The EDTA solution was prepared using 0.93 g EDTA and 4 mL of ammonia
buffer (pH = 10), which was diluted to 250 mL using distilled water. The CaCO3 solution was prepared
using 0.5 g CaCO3 and 100 mL 0.1 M HCl. The CaCO3 solution was then used to standardize the EDTA
solution, using 3 mL CaCO3 solution, 5 mL ammonia buffer, and calmagite indicator (x 3). The
standardized EDTA was then used to titrate tap water with an unknown amount of Ca2+, using 55 mL tap
water, 3 mL ammonia buffer, and calmagite indicator (x 3). One crushed antacid tablet and 5 mL
ammonia buffer were placed in a 100 mL volumetric flask and diluted using 0.1 M HCl. 5 mL of the
antacid solution, 2 mL ammonia buffer, and calmagite indicator were titrated using the standardized
EDTA solution (x 3).
Reactions:
y = EDTA
H6y2+ ↔ H5y+ + H+
H5y+ ↔ H4y + H+
H4y ↔ H3y- + H+
H3y- ↔ H2y2- + H+
H2y2- ↔ Hy3- + H+
Hy3- ↔ y4- + H+
Data:
raw data
EDTA mass (g) – 0.9406
CaCO3 mass (g) – 0.5103
Mass CaCO3 of tablet (g) – 0.5
Tablet mass (g) – 1.2636
Ammonia buffer pH – 10.10
Standardizing EDTA solution
EDTA Volume (L) CaCO3 Volume (L)
Trial 1 0.01440
0.003
Trial 2 0.01480
0.003
Trial 3 0.01470
0.003
Ammonia Buffer Volume (L)
0.005
0.005
0.005
Tap H2O titration with EDTA
EDTA Volume (L) Ammonia Buffer Volume (L)
Trial 1 0.0520
0.003
Trial 2 0.0530
0.003
Trial 3 0.0520
0.003
Tap H2O Volume (L)
0.055
0.055
0.055
Tablet solution titration with EDTA
EDTA Volume (L) Ammonia Buffer Volume (L)
Trial 1 0.01001
0.002
Trial 2 0.01229
0.002
Trial 3 0.00780
0.002
Antacid Solution Volume (L)
0.005
0.005
0.005
treated data
Concentration EDTA
(M)
Trial 1
0.0106
Trial 2
0.0103
Trial 3
0.0104
Average 0.0104
Concentration Ca2+
(M)
0.00216
0.00276
0.00216
0.00236
Hardness of water
(ppm)
86.6
111
86.6
94.7
Calculations:
Mass EDTA needed
Molar Mass EDTA
× Desired Molarity × Desired
1 mol
292.14 g
× 0.01 M × 0.25 L = 0.730 g
1 mol
Volume
Concentration of EDTA
1 mol
1
×
× Volume Used
Molar mass CaCO3
Dilution Volume
1 mol
1
1
×
× 0.003 L ×
= 0.0106 M
100.09 g
0.1 L
0.01440 L
mass CaCO3 ×
0.5103 g ×
Ca2+ concentration in tap H2O
1 mol Ca2+
1
× Dilution Volume
1 mol EDTA
1 mol Ca2+
1
× 0.25 L = 0.00216 M Ca2+
1 mol EDTA
Volume EDTA × Molarity EDTA ×
0.0520 L × 0.0104 M ×
Hardness of Water
Molar mass Ca2+
1000 mg
×
1 mol
1g
40.078 g
1000 mg
× 1 g = 86.6 ppm
1 mol
Molarity Ca2+ ×
0.00216 M ×
Reported antacid Ca2+ content
1 mol
1 mol Ca2+
Molar mass Ca2+
×
×
Molar mass CaCO3
1 mol CaCO3
1 mol
1 mol
1 mol Ca2+
40.078 g
× 1 mol CaCO × 1 mol = 0.200 g Ca2+
100.09 g
3
mass CaCO3 ×
0.5005 g ×
×
1
Volume EDTA
Tablet Ca2+ Content
(g)
0.0834
0.102
0.0650
0.0835
Weight percent Ca2+ (reported)
Mass Ca2+
Mass tablet
0.200 𝑔
×
1.2636 𝑔
× 100 %
100 % = 15.8%
Experimental antacid Ca2+content
1 π‘šπ‘œπ‘™ πΆπ‘Ž 2+
π‘šπ‘œπ‘™π‘Žπ‘Ÿ π‘šπ‘Žπ‘ π‘  πΆπ‘Ž 2+
20 π‘π‘Žπ‘Ÿπ‘‘π‘ 
×
× π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘›
1 π‘šπ‘œπ‘™ 𝐸𝐷𝑇𝐴
1 π‘šπ‘œπ‘™ πΆπ‘Ž 2+
1 π‘šπ‘œπ‘™ πΆπ‘Ž 2+
40.078 𝑔
20 π‘π‘Žπ‘Ÿπ‘‘π‘ 
×
×
= 0.0834 g
1 π‘šπ‘œπ‘™ 𝐸𝐷𝑇𝐴
1 π‘šπ‘œπ‘™ πΆπ‘Ž 2+
π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘›
Volume EDTA × π‘€π‘œπ‘™π‘Žπ‘Ÿπ‘–π‘‘π‘¦ 𝐸𝐷𝑇𝐴 ×
0.01001 L × 0.0104 𝑀 ×
Weight Percent Ca2+ (experimental)
Mass Ca2+
Mass tablet
0.0835 𝑔
×
1.2636 𝑔
× 100 %
100 % = 6.61%
Difference of weight percent
Reported percent – experimental percent
15.8% - 6.61% = 9.91%
Conclusion:
The hardness of water was determined via Ca2+ content in tap water. The average hardness of
tap water was determined to be 94.7 ppm, which is considered moderately hard by the United States
Geological Survey. Calcium content was evaluated in an antacid and compared to the manufacturer’s
claim. A difference of 9.91% was found to exist between the experimental and reported weight
percentage of calcium per tablet. The difference is rather high, which could indicate that errors occurred
in this part of the experiment.
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