Real World: Determination of Calcium in Milk
Purpose: The purpose of this experiment is to determine and compare the amount of calcium in
different types of milk. Also, the purpose was to compare two different indicators, Patton
Reeder indicator and Eriochrome Black T, when determining the amount of calcium.
Procedure:
1. Dry EDTA at 80°C overnight to create EDTA primary standard
2. Make 750mL of 0.03408M EDTA
a. 4.65g EDTA dissolved in 500mL distilled water combined with 2.3g EDTA
dissolved in 250mL distilled water
Procedure #1: Patton Reeder Indicator
1. Combine 10mL of sample, 40mL distilled water, and 4mL of 8M sodium hydroxide
solution into an Erlenmeyer flask
2. After precipitate forms, add 0.1g of Patton-Reeder indicator to flask
3. Titrate with EDTA solution
4. Repeat titration for three good trials
5. Repeat for other samples
Procedure #2: Eriochrome Black T
1.
2.
3.
4.
Add 3mL of milk and 5mL of ammonia buffer into an Erlenmeyer flask
After precipitate forms, add 0.03g Eriochrome Black T indicator
Titrate with EDTA solution
Repeat titration for three good trials
Procedure #3: Eriochrome Black T
1. Combine 10mL of Whole milk sample, 40mL distilled water, and 4mL of 8M sodium
hydroxide solution into an Erlenmeyer flask
2. After precipitate forms, add 0.1g of Eriochrome Black T indicator
3. Titrate with EDTA solution
4. Repeat for three good trials
Data:
1st Procedure
Fat Free Milk
Trial
mL EDTA added
Grams Ca2+
1
10.10
0.013795
2
10.90
0.014888
3
10.60
0.014478
4
10.70
0.014615
Avg.
----------
0.01444
Trial
mL EDTA added
Grams Ca2+
1
9.80
0.013385
2
9.78
0.013358
3
9.85
0.013454
4
9.80
0.013385
Avg.
----------
0.013396
Trial
mL EDTA added
Grams Ca2+
1
10.29
0.014055
2
10.36
0.014150
3
10.20
0.013932
4
10.20
0.013932
Avg.
-----------
0.014017
1% Milk
2% Milk
Whole Milk
Trial
mL EDTA added
Grams Ca2+
1
9.72
0.013276
2
9.47
0.012935
3
9.21
0.012580
4
9.39
0.012825
Avg.
----------
0.012904
Trial
mL EDTA added
Grams Ca2+
1
9.00
0.012293
2
9.35
0.012771
3
9.20
0.012566
4
9.00
0.012293
Avg.
----------
0.012481
Calcium Fortified
2nd Procedure
Trial
mL EDTA added
Grams Ca2+
1
5.10
0.0069659
2
4.48
0.0061190
3
4.41
0.0060234
4
4.50
0.0061464
Avg.
----------
0.0063137
3rd Procedure
There is no data for this procedure since it was a qualitative procedure. We observed no
color change from the Eriochrome Black T indicator as expected, since the suspected pH of the
sample was between 12 and 14 while Eriochrome Black T indicator changes at a pH of 10.
Calculations:
Theoretical grams of Ca2+ per serving
1,100𝑚𝑔 ×
1𝑔
= 1.1𝑔 × 0.30 = 0.33𝑔 𝐶𝑎2+
1000𝑚𝑔
Mass Ca2+
𝐿 𝐸𝐷𝑇𝐴 × 𝑀 𝐸𝐷𝑇𝐴 ×
1 𝑚𝑜𝑙 𝐶𝑎2+
× 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠
1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴
Ex. Whole Milk
1 𝑚𝑜𝑙 𝐶𝑎2+
0.00972𝐿 × 0.03408𝑀 × 1 𝑚𝑜𝑙 𝐸𝐷𝑇𝐴 × 40.078𝑔 = 0.013276𝑔 𝐶𝑎2+
Grams Ca2+ in a serving of milk
𝑎𝑣𝑔. 𝐶𝑎2+ 𝑚𝑎𝑠𝑠 240𝑚𝐿
×
10𝑚𝐿
𝑠𝑒𝑟𝑣𝑖𝑛𝑔
Ex. Whole Milk
0.012904g 240𝑚𝐿
×
= 0.3097𝑔
10𝑚𝐿
𝑠𝑒𝑟𝑣𝑖𝑛𝑔
Percent Difference
|
𝐸𝑥𝑝. 𝑚𝑎𝑠𝑠 𝐶𝑎2+ − 𝑇ℎ𝑒𝑜𝑟. 𝑚𝑎𝑠𝑠 𝐶𝑎2+
| × 100%
𝑇ℎ𝑒𝑜𝑟. 𝑚𝑎𝑠𝑠 𝐶𝑎2+
Ex. Whole Milk
0.3097 − 0.33
|
| × 100% = 6.15%
0.33
Results:
Procedure #1
Fat Free
Grams Ca2+ per
Serving
0.3466 g
1%
0.3215 g
2.58%
2%
0.3364 g
1.94%
Whole
0.3097 g
6.15%
Calcium Fortified
0.2995 g
9.23%
Milk
Percent Difference
5.02%
Procedure #2
Whole Milk
Grams Ca2+ per Serving
Percent Difference
0.1515 g
54.1%
Conclusion:
The purpose of this experiment was to determine and compare the calcium content of
different types of milk using a complexometric titration, and to compare two different indicators.
We found that the complexometric titration is a successful method to use to determine the
calcium content of milk since our percent differences were relatively small. The largest percent
difference came from the second procedure, where we used Eriochrome Black T (EBT) indicator
instead of Patton-Reeder. This showed us that it was necessary for us to order the Patton-Reeder
indicator since this procedure did not work with EBT.
To determine the percent difference, we had to determine the theoretical amount of
calcium in milk. We found that for a 2,000 calorie diet, a person needs a daily calcium intake of
1,100mg. On our milk cartons, they claimed to have 30% of your daily calcium intake.
Therefore, we took 1.1g and multiplied it by 30% to get a theoretical value of 0.33g of calcium.
There were multiple possible sources of error for this experiment. The biggest source of
error was using the indicators. The color change for these indicators was very hard to read since
the color was supposed to change from a dark purple to a dark blue. This was the case for both
indicators. In the future, it would be better to use an indicator with a more distinct color change.
Another source of error came from the titrations. We could have read the buret wrong or we
could have ended it too soon or too late.