Real World: Determination of Calcium in Milk
By Delaney Caudill, Ethan Nichols, and Katie Vautier
BackgroundMethods Considered• Ion Selective Electrode Method• Trichloroacetic Acid Filtrate Method– Use of this acid as a protein precipitator to
determine calcium content• Complexometric Titrations– A volumetric analysis in which a formation of a
colored complex is used to indicate the end point of a titration
Purpose
• Determine and compare the calcium content via a complexometric titration to listed values of different types of milk
• Compare two different indicators
Procedure #1: Patton-Reeder
• Dry EDTA at 80°C overnight• Make 750mL of 0.03408M EDTA• Combine 10mL of sample, 40mL distilled
water, and 4mL of 8M sodium hydroxide solution into an Erlenmeyer flask
• Add 0.1g of Patton-Reeder indicator • Titrate w/ EDTA solution
Data
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
Whole Milk
% Difference
• Fat free milk: 5.1%• 1% milk: 2.5%• 2% milk: 2.0%• Whole milk: 6.2%• Calcium Fortified: 9.0%
Before Titration
After Titration
Color Change?
Procedure #2: Eriochrome Black T
• Add 3mL of milk and 5mL ammonia buffer in a 250mL Erlenmeyer flask
• Calibrate a pH meter and measure pH of each sample (needs to be 10)
• Add 0.03g of indicator• Titrate with EDTA
Data
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
Whole Milk
Results
• Whole milk: 54.1%• Makes sense due to different indicator (EBT)– pH of sample was 10– pH had effect on sample?
Procedure #3: Eriochrome Black T• Same as procedure #1 except used different
indicator: Eriochrome Black T
Data & Results
• No quantitative data• No color change due to the solution having a
pH between 12 and 14• Eriochrome Black T indicates a color change at
a pH of 10
No Color Change
Theoretical Grams of Ca per Serving• Based on a 2,000 calorie diet, daily calcium
intake should be 1,100mg• Each milk carton claims it contains 30% of
daily calcium intake
Example Calculations
• Grams Ca2+ in a serving of milk
• Ex. Whole Milk
• Percent Difference
• Ex. Whole Milk
Sources of Error
• INDICATORS!– Subjective color change
• Different people titrated samples• Reading the buret• Wait for precipitate to come out of solution to
‘remove’ magnesium oxide
Future Work
• Investigate different indicators• Change pH of samples to use Eriochrome
Black T indicator by changing molarity of NaOH
• Try other calcium supplements such as vitamins or orange juice
Conclusion
• Successful experiment– Efficient method: complexometric titration– Low percent differences
• Necessary to order Patton Reeder since Eriochrome Black T yielded higher percent difference
References
• Harris, Daniel C. Quantitative Chemical Analysis, 8th ed.; W.H. Freeman and Company: New York, 2010, page 240.
• http://www.chemteach.ac.nz/invesigations/documents/calcium.pdf
• http://www.jbc.org/content/90/3/747.full.pdf
Special Thanks
• Dr. Peterman• Melissa, Kate, Pat, and Kiersten• Professor Mowery
Questions?
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