Experiment 10: Real-World Project
Andrew Mullenax
Purpose:
The purpose of this experiment is to determine the amount of calcium and vitamin C in two
different commercial multivitamin tablets by means of EDTA and iodimetric titration.
Procedure:
Standardization of EDTA:







Calibrate a pH meter with several standard solutions until the pH of 6M ammonia buffer
can be determined.
Add concentrated HCl to the ammonia buffer until a pH of about 10 is reached.
Weigh out approximately 0.09360g of EDTA and add 4mL of 6M ammonia buffer in a
250mL Erlenmeyer flask then fill to the mark.
Prepare a calcium chloride solution by mixing approximately 0.5000g of calcium
carbonate with 100mL of 0.1M HCl.
Place 3mL of the CaCl2 solution in a 250mL Erlenmeyer flask with 5mL of ammonia
buffer and a small amount calmagite indicator.
Titrate the solution with the EDTA solution until the violet turns to a purple/blue color.
Repeat for three good trials.
Calcium Determination:





Crush and weigh a multivitamin tablet.
Place crushed tablet in a 100mL volumetric flask. Add 5mL of 6M ammonia buffer and
dilute to the line with 0.1M HCl.
Place 5mL of this solution in a 250mL Erlenmeyer flask and add 2mL of ammonia buffer
and a few drops of calmagite indicator.
Titrate with EDTA until the solution turns a purple/blue color.
Repeat for three good trials for each multivitamin.
Standardization of Thiosulfate:




Prepare a starch indicator solution by making a paste of 2.5g soluble starch in 25mL of
water. Pour into 500mL of boiling water then boil until clear.
Prepare approximately 0.07M thiosulfate solution by dissolving an accurately weighed
sample of about 8.70g of Na2S2O3·5H2O in 500mL of freshly boiled water containing
0.05g of Na2CO3.
Prepare approximately 0.01M KIO3 by weighing about 1g of solid reagent and dissolving
it in a 500mL flask.
Pipet 50.00mL of KIO3 solution into an Erlenmeyer flask and add 2g solid KI and 10mL
of 0.5M H2SO4.


Immediately titrate with thiosulfate until the solution until the solution loses almost all of
its color. Add 2mL of starch indicator and complete the titration.
Repeat for three good trials.
Vitamin C Determination:




Crush and weigh an appropriate amount of the multivitamin tablet for a 25mL titration.
Dissolve this in 50mL of 0.3M H2SO4 while stirring.
Add 2.0g of KI and 50mL of 0.01M KIO3 and titrate with the standardized thiosulfate
solution adding 2mL of starch indicator just before the endpoint.
Repeat this for three good trials for each multivitamin.
Data:
EDTA Standardization
Mass EDTA = 0.9400g
Trial
Volume EDTA
added(mL)
Molarity EDTA (M)
Average Molarity (M)
Thiosulfate Standardization
Trial
1
2
3
Average
1
2
3
15.41
14.34
14.70
.0097
.0104
.0101
.0102
Volume Thiosulfate(mL)
38.10
39.15
39.55
38.93
Molarity Thiosulfate(M)
.074
.0720
.0713
.0724
Titration of CareOne multivitamin with thiosulfate
Volume
Mass of
Trial
Thiosulfate(mL)
vitamin
1
2
37.12
.0934
3
40.01
.0991
Average
38.57
0.0963
Mass Ascorbic
acid(mg)
45.2
24.7
34.95
Wt% of Ascorbic
acid in tablet
12.5
6.82
9.66
Titration of NatureMade multivitamin with thiosulfate
Volume
Trial
Mass of vitamin
Thiosulfate(mL)
1
40.00
.0937
2
39.83
.0946
3
40.00
.0995
Mass Ascorbic
acid(mg)
56.4
59.5
71.1
Wt% of Ascorbic
acid in tablet
4.21
4.45
5.31
Average
39.94
0.0959
62.33
Titration of CareOne multivitamin with EDTA
Volume EDTA
Mass of
Trial
(mL)
Calcium(mg)
1
5.68
46.1
2
6.40
51.9
3
6.51
52.8
Average
6.2
50.27
Wt% of Calcium
in tablet
12.7
14.3
14.6
13.87
Titration of NatureMade multivitamin with EDTA
Volume EDTA
Mass of
Trial
(mL)
Calcium(mg)
1
23.00
258.24
2
24.00
269.47
3
23.50
263.86
Average
23.50
263.86
Wt% of Calcium
in tablet
19.3
20.1
19.7
19.7
4.66
Calculations:
Molarity of EDTA:
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝑎
1
× .003𝐿 ×
. 1𝐿
𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝐸𝐷𝑇𝐴
. 00014985𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝑎
1
× .003𝐿 ×
= .0972𝑀
. 1𝐿
. 01541𝐿 𝐸𝐷𝑇𝐴
Molarity Thiosulfate:
3 𝑚𝑜𝑙 𝐼3−
2 𝑚𝑜𝑙 𝑆2 𝑂32−
1
𝑚𝑜𝑙𝑒𝑠 𝐾𝐼𝑂3 ×
×
×
= 𝑚𝑜𝑙𝑎𝑟𝑖𝑡𝑦
1 𝑚𝑜𝑙 𝐾𝐼𝑂3
1 𝑚𝑜𝑙 𝐼3−
𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝑡ℎ𝑖𝑜𝑠𝑢𝑙𝑓𝑎𝑡𝑒
. 00047𝑚𝑜𝑙𝑒𝑠 𝐾𝐼𝑂3 ×
3 𝑚𝑜𝑙 𝐼3−
2 𝑚𝑜𝑙 𝑆2 𝑂32−
1
×
×
= .0740𝑀
−
1 𝑚𝑜𝑙 𝐾𝐼𝑂3
1 𝑚𝑜𝑙 𝐼3
. 03915
Mass of Calcium in multivitamin:
𝐿 𝑜𝑓 𝐸𝐷𝑇𝐴 × 𝑚𝑜𝑙𝑎𝑟𝑖𝑡𝑦 𝐸𝐷𝑇𝐴 ×
1 𝑚𝑜𝑙 𝐶𝑎
20 𝑝𝑎𝑟𝑡𝑠 40.1𝑔 𝐶𝑎 1000𝑚𝑔
×
×
×
= 𝑚𝑎𝑠𝑠 𝐶𝑎
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴 1 𝑡𝑎𝑏𝑙𝑒𝑡
1 𝑚𝑜𝑙
1𝑔
. 00568𝐿 𝐸𝐷𝑇𝐴 × .0101𝑀 ×
1 𝑚𝑜𝑙 𝐶𝑎
20 𝑝𝑎𝑟𝑡𝑠 40.1𝑔 𝐶𝑎 1000𝑚𝑔
×
×
×
= 46.1𝑚𝑔
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴 1 𝑡𝑎𝑏𝑙𝑒𝑡
1 𝑚𝑜𝑙
1𝑔
Weight percent of Calcium:
𝑚𝑎𝑠𝑠 𝐶𝑎
× 100
𝑚𝑎𝑠𝑠 𝑡𝑎𝑏𝑙𝑒𝑡
. 0461𝑔 𝐶𝑎
× 100 = 12.7% 𝐶𝑎𝑙𝑐𝑖𝑢𝑚
. 3618𝑔
Mass of Vitamin C in multivitamin:
𝐿 𝑡ℎ𝑖𝑜𝑠𝑢𝑙𝑓𝑎𝑡𝑒 × 𝑀 𝑡ℎ𝑖𝑜𝑠𝑢𝑙𝑓𝑎𝑡𝑒 ×
1 𝑚𝑜𝑙 𝐼3−
= 𝑒𝑥𝑐𝑒𝑠𝑠 𝐼3−
2 𝑚𝑜𝑙 𝑆2 𝑂32−
. 03712𝐿 𝑡ℎ𝑖𝑜𝑠𝑢𝑙𝑓𝑎𝑡𝑒 × .0724𝑀 𝑡ℎ𝑖𝑜𝑠𝑢𝑙𝑓𝑎𝑡𝑒 ×
𝑇𝑜𝑡𝑎𝑙 𝐼3− = .0094𝑀 𝐾𝐼𝑂3 × .05𝐿 𝐾𝐼𝑂3 ×
1 𝑚𝑜𝑙 𝐼3−
= .001344 𝑚𝑜𝑙 𝐼3−
2 𝑚𝑜𝑙 𝑆2 𝑂32−
3 𝑚𝑜𝑙 𝐼3−
= .00141 𝑚𝑜𝑙 𝐼3−
1 𝑚𝑜𝑙 𝐾𝐼𝑂3
𝐼3− 𝑟𝑒𝑎𝑐𝑡𝑒𝑑 = .00141 − .001343 = 6.6 × 10−5 𝑚𝑜𝑙 𝐼3−
1 𝑚𝑜𝑙 𝐴𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝑎𝑐𝑖𝑑 𝑡𝑜𝑡𝑎𝑙 𝑣𝑖𝑡𝑎𝑚𝑖𝑛 𝑚𝑎𝑠𝑠
176.12𝑔
×
×
1 𝑚𝑜𝑙 𝐼3−
𝑚𝑎𝑠𝑠 𝑢𝑠𝑒𝑑 𝑖𝑛 𝑡𝑟𝑖𝑎𝑙 1 𝑚𝑜𝑙 𝑎𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝑎𝑐𝑖𝑑
= 𝑚𝑎𝑠𝑠 𝑎𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝑎𝑐𝑖𝑑
𝑚𝑜𝑙𝑒𝑠 𝐼3− ×
1 𝑚𝑜𝑙 𝐴𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝑎𝑐𝑖𝑑 . 3618𝑔
176.12𝑔
1000𝑚𝑔
×
×
×
−
1 𝑚𝑜𝑙 𝐼3
. 0934𝑔 1 𝑚𝑜𝑙 𝑎𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝑎𝑐𝑖𝑑
1𝑔
= 45.2𝑚𝑔 𝐴𝑐𝑜𝑟𝑏𝑖𝑐 𝐴𝑐𝑖𝑑
6.6 × 10−5 𝑚𝑜𝑙 𝐼3− ×
Weight percent of Ascorbic Acid:
𝑚𝑎𝑠𝑠 𝐴𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝐴𝑐𝑖𝑑
× 100
𝑚𝑎𝑠𝑠 𝑡𝑎𝑏𝑙𝑒𝑡
. 0452𝑔
× 100 = 12.5% 𝐴𝑠𝑐𝑜𝑟𝑏𝑖𝑐 𝐴𝑐𝑖𝑑
. 3618𝑔
Conclusion:
The purpose of this lab was to determine the calcium and vitamin C content of to commercially
available multivitamin tablets through EDTA and iodimetric titrations. For the CareOne
multivitamin we determined the calcium and vitamin C content to be 13.87% and 9.66%
respectively. For the NatureMade multivitamin we determined the calcium and vitamin c content
to be about 19.7% and 5.31% respectively. For the CareOne multivitamin our calcium
determination was relatively close to the reported value of 12.4%. The calcium determination for
NatureMade was significantly greater probably due to the fact that the vitamin contained a
variety of different metals that would have complexed with EDTA giving us skewed results. The
vitamin c determinations for both multivitamins were significantly lower than the reported value
by the manufacturer. This is most likely due to the fact that we overshot the endpoint for each of
the titrations.