Transcript
Quantity of Calcium and Magnesium ion in Milk
An investigation into differing quantities of Calcium and Magnesium ions in eight types of milk drinks produced in Korea. Hyo Jung Kim 2012-2014 Extended Essay
Word Count: 3947
Abstract This essay examines the different quantities of Calcium and Magnesium ions found in eight types of milk drinks d rinks produced in Korea. They The y are; No fat Maeil, Low fat Maeil, Original Maeil, Seoul, Jeju, Strawberry, Maeil Banana and Hershey chocolate drink. In exploring this research topic, the chemical properties of the EDTA molecule: Ethylenediaminetetraacetic acid, are discussed. For the ex periment, EDTA titration is used along with Eriochrome Black T indicator, which changes from purple to blue at an endpoint.
The molar ratio of the EDTA molecule and calcium/magnesium is 1:1.From the change in volume of EDTA data, I calculated the mass of calcium and magnesium per 10 3
cm of milk, using stiochiometric equations. I utilized the information from one report, which said that calcium ions are approximately 10 times larger than magnesium ions. Through this calculation, I ranked which milk brand contained the highest quantity of calcium and magnesium to the lowest. The milk with the highest h ighest mass of metal ions was Low fat Maeil while the Jeju milk h ad the least.
While analyzing the data from the experiment, I noticed that the theoretical values, the manufacturer ’s claims for calcium content, were different from the data that I gained from the experiment. In this regard, original Maeil was the most accurate, having only a 4% difference. On the other hand, No fat Maeil was the least accurate, having havin g more than 50% difference.
Word count: 231
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Table of Contents Introduction ------------------------------------------------------------------------------------------------------------------------------------p3-4 ---------------------p3-4 EDTA ----------------------------------------------------------------------------------------------------------------------------------------------------p5-7 ---------------------p5-7 Analytical techniques -------------------------------------------------------------------------------------------------------------p7-8 --------------------p7-8 -EDTA titration----------------titration-------------------------------------------------------------------------------------------------------------p7-8 --------p7-8 -Atomic absorption spectrophotometer (AAS) -------------------------------------------------------------p8 -p8
Investigation ----------------------------------------------------------------------------------------------------------------------------------------p8-13 ---------p8-13 Data collection and analysis ------------------------------------------------------p14-23 Evaluation – --------------------------------------------------------------------------p23-32 --------------------------------------------------------------------------p23-32 Conclusion -----------------------------------------------------------------------------------------------------------------------------------------p33 ----------------------p33 Appendix ---------------------------------------------------------------------------- p34-35 Bibliography --------------------------------------------------------------------------------------------------------------------p36-39 -----------------------------p36-39
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Introduction The research question for this essay is “An “An investigation into the differing quantities of Calcium and Magnesium ions in eight types of milk drinks produced in Korea.” Korea.” Calcium is a mineral that is essential for the human body. It comprises 1.5 to 2.0 % 1
2
of our body weight. It is required by the body to produce strong bones and teeth .
Calcium is also used in blood clotting, hormone release, regulation of enzymes and cell 3
division. Similarly, magnesium is beneficial to human bodies since it dilates (opens up) 4
blood vessels in the heart, arms and legs. Hence, one research shows that a lack of magnesium is associated with fatigue, pain, weakness, muscle spasms, irritability, and 5
numbness.
This investigation will compare the quantity of calcium and magnesium in different types of milk. Eight different brands of milk were chosen. Five of them are plain milk: No fat Maeil, Seoul, Jeju, Original Maeil, and low fat Maeil while three are flavored milk: Maeil Banana, Maeil Strawberry, Maeil Hershey Chocolate Drink. These were chosen because according to the milk cartons, they mostly contained different quantities of calcium. The main chemical equation of the experiment is: 4-
2-
2-
MIn(aq) + EDTA (aq)=> MEDTA (aq) + In (aq) 1 Elias,
A.J. (2002). A (2002). A Collection of Interesting Interesting General General Chemistry Experiments. Experiments . Hyberabad, India: University Press (India) Private Limited. p14 2 Ibid p. 14 3 Ibid p. 14 4 Fuchs, N.K. (2002). User's Guide to Calcium and Magnesium. Magnesium . New Jersey: Basic Health Publications, Inc. p29. 5 Ibid p. 56 3
2+
2+
M can be either Ca or Mg .
The calcium and magnesium content of each milk was found by titrating 0.025 3
mol/dm of EDTA, etylenediaminetraacetic acid solution, which, according to IUPAC id is 2,2',2'',2'''-(Ethane-1,2-diyldinitrilo) tetraacetic acid. Eriochrome Black T indicator and pH 10 buffer solutions were added. Before carrying out an experiment, the essay will discuss the nature of 2,2',2'',2'''-(Ethane-1,2-diyldinitrilo) tetraacetic acid. acid. I will examine two analytical techniques: EDTA titration and Atomic Absorption Spectroscopy that are utilized to determine the concentration of calcium and magnesium in milk. I was interested in titration because titration can detect the end point of EDTA-metal complex with the naked eye and it is an accurate chemical technique.
An investigation into calcium and magnesium content of milk was chosen because it is widely acknowledged that milk contains high quantities of calcium. As a chemist, I was curious about the debate over the effectiveness of higher calcium content in milk, so this experiment would show whether the milk has a large quantity of calcium and magnesium to make our bodies healthy. The recommended daily allowance (RDA) for calcium is 1,000 milligrams for young adults and 1,200 for adults 50 and over. 6 This experiment will assess how much content of milk has to be consumed to achieve recommended daily allowance.
This investigation is significant because there has been no research done on determining calcium and magnesium quantities in eight t ypes of Korean milk brands.
6 Woolston,
C. (2010). Milk: How much should you drink?. Available: http://articles.latimes.com/2010/jul/12/health/la-he-milk-amount-20100712. Last accessed 12th Oct 2013. 4
EDTA
http://whatcom.ctc.edu/files/9713/3677/3232/EDTA_titration_lab.pdf Figure 1: Complete structure of EDTA EDTA is also known as Ethylenediaminetetraacetic acid and its IUPAC id is 2,2',2'',2'''-(Ethane-1,2-diyldinitrilo) tetraacetic acid acid . It has a molecular formula of C10H16 N2O8. The molecule’ molecule’s structure contains four carboxylic acids and two amino 7
groups. What is more, EDTA is a powerful chelating agent that wraps round metal ions 8
like a claw . Chelation is the formation or presence of bonds (or other attractive interactions) between two or more separate binding sites within the same ligand and a single central single central atom.
9
7 Natural
answer. (no date). What is EDTA? Available: Available: http://naturalanswer.com/edta.htm. http://naturalanswer.com/ edta.htm. Last accessed 27th May 2013. 8 Whatcom Community College. (no date). Determination of Ca 2+ and Mg 2+ in Water. Available: http://whatcom.ctc.edu/files/9713/3 http://whatcom.ctc.edu/files/9713/3677/3232/EDTA_titration_lab.p 677/3232/EDTA_titration_lab.pdf. df. Last accessed 26th Jun 2013. 9 IUPAC. (2012). Chelation. Available: Chelation. Available: http://goldbook.iupac.org/C01012.html. http://goldbook.iupac.org/C01012.html. Last accessed 12th Oct 2013. 5
EDTA is a polydentate ligand, a compound that has six pairs of valence electrons. It can form six bonds, two from nitrogen atoms in amino groups and four from oxygen 10
atoms in carboxyl groups, when the molecule binds to metal ions. It can form bonds 2+
2+
2+
with many metal ions such as Ca , Mg , Fe etc. When bonded to a metal ion, the ion is attached in the center of EDTA structure.
http://www.benbest.com/nutrceut/EDTA.html Figure 2: EDTA around Metal ion. When a metal ion is attracted to EDTA, the orbitals are not hybridized. However, d-orbital in the metal distorts its shape.
10 Whatcom
Community College. (no date). Determination of Ca 2+ and Mg 2+ in Water. Available: http://whatcom.ctc.edu/files/9713/3 http://whatcom.ctc.edu/files/9713/3677/3232/EDTA_titration_lab.p 677/3232/EDTA_titration_lab.pdf. df. Last accessed 26th Jun 2013. 6
Since 2,2',2'',2'''-(Ethane-1,2-diyldinitrilo) tetraacetic acid acid forms complex ions 11
12
with many metal ions and is relatively inexpensive , it has many uses. To be more specific, Food Grade EDTA is used to protect us to some degree de gree from harmful metals that find their way into the foods we eat.
13
Moreover, EDTA is used to treat heavy metal
poisoning or toxicity like zinc and aluminum.
Different Analytical Techniques The two most common techniques used to find the total concentration of calcium and magnesium ions are EDTA titration and Atomic Absorption Spectrometry. This section will explain the procedures; assess the advantages and disadvantages of each method. Eventually, EDTA titration was chosen simply because the school didn’ didn’t have an atomic absorption spectrometer.
1. EDTA titration with black Eriochrome indicator 4-
EDTA ion, EDTA bonds to Calcium and Magnesium ions. Eriochrome Black T (ErioT) is used as the indicator. It is also a ligand that forms a complex with metal ions. 14
But it binds to metal less strongly than EDTA. Before the titration, the indicator forms a complex with magnesium and calcium ions. When this happens, a red-wine colour will appear. As titration takes place, EDTA ligand forms a complex with free metal ions. Then, 11 Annenberg
Learner. (no date). Chapter 13: EDTA titrations. Available: titrations. Available: http://www.learner.org/workshops/chemistry/channeltalk/att-0194/01EDTA_titrations.pdf. Last accessed 17th Sept 2013. 12 Elias, A.J. (2002). A (2002). A Collection of Interesting Interesting General General Chemistry Experiments Experiments.. Hyberabad, India: University Press (India) Private Limited.p14 13 Natural answer.(no date). How does it work to remove Metal? Available: Available: http://naturalanswer.com/edta.htm. http://naturalanswer.com/ edta.htm. Last accessed 28th May 2013. 14 Elias, A.J. (2002). A (2002). A Collection of Interesting Interesting General General Chemistry Chemistry Experiments. Experiments . Hyberabad, India: University Press (India) Private Limited. p14 . p15 7
it forms complex with the metal-indicator complex.
15
This method is useful since there is
less equipment needed to carry out the experiment. Furthermore, the results are relatively accurate and reliable.
2. Atomic Absorption Spectrometry (AAS) Another technique to detect calcium and magnesium content in milk is through Atomic Absorption Spectrometry. It is a measured by absorption of the energy required to raise electrons to a higher energy energ y excited state.
16
AAS is an extremely sensitive method. Thus, its advantage of it is the results are more precise than through EDTA titration. To be more specific, its concentration can be measured as low as one part per billion.
17
Also, AAS can determine more than two
elements in the sample solution (on average five elements) while EDTA titration is limited to determining two or three elements. Another benefit of using AAS is that the concentration results come out quickly.
18
Investigation Materials 3 200 cm of eight types of milk Ammonium chloride buffer pH 10 solution 3 0.025 mol/dm EDTA solution Eriochrome Black T indicator 3 1 10 cm measuring cylinder
15
Kenkel, J (2010). Analytical Chemistry for Technicians. 3rd ed. Florida: CRC press. p. press. p. 122
16
Marth,H.E. (1988). Fundamentals (1988). Fundamentals of Dairy Chemistry. Chemistry. New York : Apsen publishers Inc. p. 6 17 Brown, C and Ford, M (2009). Pearson Baccalaureate Chemistry Higher Level . Level . Edinburgh Gate, Harlow: Pearson Education Limited. p457. 18 ibid. P. 457
8
3
1 25 cm measuring cylinder 3 1 50 cm conical flask 1 pH meter 3 1 50 cm burette 1Cling stand 3 1 50 cm beaker 1 dropping pipette
Preparations of sample solutions: 19
Eight different types of milk were purchased from Jeju supermarket to prepare for samples. These types of milk were chosen because they are the most common brands in Korea.
Method 3
3
1. Measure 10 cm of sample milk using 10 cm measuring cylinder. Add it in 50 3
cm conical flask. 3
3
2. Measure 16.67 cm of ammonium pH 10 buffer using 25 cm measuring cylinder. Add it in the flask where milk sample is contained 3. Add 5 drops of Eriochrome Black T indicator using a dropping pipette. When the indicator is added, it forms complex with magnesium and calcium ions. In this process, it turns purple. 3
4. Calibrate the pH meter with distilled water in 50 cm beaker. 5. Measure the pH of the solution using a pH meter. 3
6. Record the initial volume of 0.025 mol/dm of EDTA in the burette.
19 No
fat Maeil, low fat Maeil, original (whole) Maeil, Seoul, Jeju, Maeil strawberry, strawberry, Maeil banana and Maeil Hershey chocolate choco late milk
9
7. Titrate EDTA until the color of the solution turns from purple to blue. At this point, the magnesium and calcium ions that were in complex with indicator are 4-
2-
2-
transferred to EDTA ions to form MgEDTA or CaEDTA . 8. Measure the pH of the solution titrated with EDTA using the pH meter. The difference of pH measured at this stage and pH measured initially should be around 2. 9. Record the final reading of EDTA. 10. Repeat the procedure 1 to 9 using different brands of milk each time. Each type of milk will be experimented three times.
Explanation for method Quantities of milk, ammonium buffer and drops of Eriochrome Black T indicator were adapted using information from a power-point on the internet,
20
Real World:
Determination of Calcium in Milk by Delaney Caudill, Ethan Nichols and Katie Vautier.
20 Caudill,
D., Nichols, E and Vautier K. (no date). Real World: Detmerination of Calcium in Milk. Available: Milk. Available: http://www.google.co.kr/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&c ad=rja&ved=0CCYQFjAA&url=http%3A%2F%2Fstudents.ycp.edu%2F~dcaudill%2 FReal%2520World%2520Powerpoint.pptx&ei=ErRWUtyJM FReal%2520World%2520Powerp oint.pptx&ei=ErRWUtyJM8WikwXwxoGgB. 8WikwXwxoGgB. Last accessed 15th May 2013. 10
3
3
Initially, the guideline from the PowerPoint was to add 3 cm of milk and 5 cm 3
ammonia buffer in a 250 cm Erlenmeyer flask. From this, the quantity of milk and ammonium chloride needed in the experiment was calculated: Milk= 3:10 Ammonia buffer= 5: x 3:10= 5: x X=
= 16.67
As for the indicator, the resource stated to add 0.03g of EBT indicator. Assuming that 0.03 g was about 1.5 drop, the number of drops for the indicator was adjusted: Milk= 3:10 Indicator= 1.5: y 3:10= 1.5: y 15= 3y Y=5 3
3
Thus, 10 cm of milk sample, an estimated 16.67 cm of pH 10 ammonia buffer and 5 drops of Eriochrome Black T indicator was need ed for the experiment. 11. The steps from 4 to 7 are similar to the presentation while step 8 was designed by me to keep the pH difference at approximately 2.00.This was because if the pH change before and after the titration varied to 2 to 5 and was not recorded, the results may be inaccurate taking into account that the milk sample in each trial is 3
only 10 cm . It is important to keep pH constant to 10 to form very stable
11
complexes.
21
4-
This is because it results in increased EDTA concentration which
favors complex formation.
22
Also, the color change of the indicator from magenta
to blue occurs at pH above 7 and at this pH, precipitation of hydroxides does not 23
occur. (see Appendix 1)
Hypothesis According to one article in dailymail.co.uk, it stated “skimmed “skimmed milk has a little more calcium than semi-skimmed which in turn has a little more calcium than whole who le milk. 24
3
An analysis shows that the difference is slight; per 100 cm the figures are 122mg for
skimmed milk, 120 mg for semi-skimmed milk and 118 mg for whole.
25
Thus, I assume
that the calcium content of no fat, low fat and original Maeil milk will not differ much. Yet there should a minor difference about 0.2 mg change among these brands.
26
Risk assessment:
21 Elias,
A.J. (2002). A (2002). A Collection of Interesting Interesting General General Chemistry Experiments. Experiments . Hyberabad, India: University Press (India) Private Limited. p14 22 ibid. p14 23 ibid. p14 24 Mail online.(no date). Which milk has the most calcium?. Available: calcium?. Available: http://www.dailymail.co.uk/femail/article-197372/Which-m http://www.dailymai l.co.uk/femail/article-197372/Which-milk-calcium.html. ilk-calcium.html. Last accessed 15th July 2013. Skimmed milk is also known for no fat milk, semi-skimmed milk as low fat milk and whole milk as original milk. 25 ibid. 26 In the experiment, only 10 cm3 of milk is measured so the figure of calcium content in milk has to be divided by 10, making 12.2 mg, 12.0 mg and 11.8 mg, making However, the numbers are approximate values so it is not very accurate. 12
Do not drink leftover milk sample that was used in the experiment. The milk may contain some chemicals such as EBT indicator, ammonium buffer or EDTA solution. Wear goggles to prevent ammonium buffer solution splattering into the eyes. Wear a lab coat and tie hair back in case the chemicals spill on hair or on clothes. Do not contact with ammonium chloride buffer solution. It will be irritating to the skin and eyes when in contact with the chemical.
27
27 Pestell
Minerals & ingredients . (2009). MSDS-Ammonium Chloride AF. Available: AF. Available: http://www.pestell.com/msds/Ammonium_Chlorid http://www.pestell.com/ msds/Ammonium_Chloride.pdf. e.pdf. Last accessed 12th Oct 2013. 13
Data collection and Analysis Table 1: Raw Data Table Type of Initial Milk EDTA volume 3 (cm , No fat 20.60 Maeil 32.40 2.10 Low fat 16.60 Maeil 32.90 10.80 Original 10.50 Maeil 7.80 31.80 Seoul 0.30 12.30 20.80 Jeju 11.70 30.10 39.10 Strawberry 1.00 14.80 26.00 Maeil 2.40 Banana 14.10 25.40 Hershey 33.50 Chocolate 1.70 14.10
Final EDTA volume 3 (cm , 32.40 43.40 12.30 32.90 45.00 26.00 20.60 18.70 41.50 10.50 20.80 30.10 21.00 39.10 47.30 14.80 26.00 39.80 14.10 25.40 37.40 45.00 13.10 25.20
Change in EDTA volume 3 (cm , 11.8 11.0 10.2 16.3 12.1 15.2 10.1 10.9 10.3 10.2 7.5 9.3 9.3 9.0 8.2 13.8 12.2 13.8 11.7 11.3 12.0 11.5 11.4 11.1
Initial pH (
Final pH (
9.585 9.555 9.560 9.580 9.650 9.650 9.480 9.600 9.555 9.435 9.490 9.475 9.555 9.590 9.500 9.500 9.710 9.720 9.360 9.460 9.530 9.660 9.570 9.590
7.460 7.460 7.390 7.120 7.515 7.410 7.155 7.180 7.190 7.125 7.275 7.200 7.430 7.445 7.350 7.160 7.480 7.290 7.315 7.180 7.370 7.270 7.370 7.320
Change in pH ( )
2.125 2.095 2.170 2.460 2.135 2.240 2.325 2.420 2.365 2.310 2.215 2.275 2.125 2.145 2.150 2.240 2.230 2.430 2.045 2.280 2.160 2.390 2.200 2.270
The content of Calcium and Magnesium is found using the stoichiometry in the formula, 4-
2-
2-
MIn(purple, aq) + EDTA (aq) => MEDTA (aq) + In (blue,aq) 2+
2+
M can be Ca or Mg . 4-
The mole of EDTA is found using the equation,
14
Number of moles = concentration volume n (mol) = CV 2+
4-
2+
4-
The proportion of the coefficient of Ca to EDTA is 1:1 and Mg to EDTA is 1:1.The volume is the change of EDTA volume shown in table 1. For instance, the volume of no n o fat Maeil milk was 11.8 ml. 3
3
3
11.8 cm = 11.8 10 dm
dm3 = 0.0118 4-
3
In addition, the concentration of EDTA used in the experiment was 0.025 moles per dm .
-
EDTA 0.000295 0.025 0.0118 0.0118
Number of Moles (n, mol) Concentratio Concentration n (c, mol/dm ) Volume Volume (V,dm (V,dm ) 2+
2+
Yet, since Ca and Mg were detected simultaneously, the calculation for each metal ion should be different. According to my research, the average concentration of 2+
Ca
2+
is 119.8 mg while Mg
content is 11.2 mg.
28
Using this information, the calcium
and magnesium ion will be calculated separately. The mass of calcium is found by multiplying magnesium, multiply
4-
to the moles of EDTA . For
Calcium ion: 0.000295
Magnesium ion:
28 United
States Department of Agriculture. (no date). Calcium and magnesium content of milk . Available: http://ndb.nla.usda.gov/ndb/foods/show/154?qlook http://ndb.nla.usda.gov/n db/foods/show/154?qlookup=01175&max=25&man=&If up=01175&max=25&man=&If acet=&new=1.Last accessed 29th Sept 2013. 15
0.000295
= 0.000025 mol +
Moles (n, mol) Molar Mass (Mr, g/mol) Mass (M,g)
Ca 0.000270 40.08 0.010813
Moles (n, mol) Molar Mass (Mr, g/mol) Mass (M,g)
Mg 0.000025 24.31 0.000613
+
Now the mass of it is found, using another stoichiometric equation, Mass = Number of Moles Molar Mass E.g. No fat Maeil’ Maeil’s calcium’ calcium’s Mass= 0.000265 40.08 = 0.010813 grams =10.81 mg The percentage content of calcium and magnesium is calculated as
e.g.No fat Maeil
Table 2: Processed Data Table
16
Type of milk
Mass of Calcium 3 (mg/10 cm )
Mass of Magnesium 3 (mg/10 cm )
No fat Maeil
10.81 10.08 9.35 14.94 11.09 13.93 9.25
0.61 0.57 0.53 0.85 0.63 0.79 0.53
Mass of calcium and magnesium 3 (mg/10 cm ) 11.42 10.65 9.88 15.79 11.72 14.72 9.78
9.99
0.57
10.56
9.44
0.54
9.98
9.35
0.53
9.88
6.52
0.39
6.91
8.52
0.48
9.00
8.52
0.48
9.00
8.25
0.47
8.72
7.51
0.43
7.94
12.65
0.72
13.37
11.18
0.63
11.81
12.65
0.72
13.37
10.72
0.61
11.33
10.36
0.59
11.95
11.00
0.62
11.62
10.54
0.60
11.14
10.45
0.59
11.04
10.17
0.58
10.75
Low fat Maeil
Original Maeil
Seoul
Jeju
Strawberry
Banana
Hershey Chocolate
Average percentage content (%) 0.107
0.141
0.101
0.086
0.085
0.129
0.116
0.110
17
Aver A verage age percentage percentage abundance abundance of calcium and magnesium ions 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0
Average percentage abundance of calcium and magnesium ions
Graph 1: Average percentage content of Calcium and magnesium (%) This bar chart and processed data table illustrate that the milk with the highest concentration of magnesium and calcium is Low fat Maeil which contains in average 3
0.141 % of the two minerals in 100 cm of milk. Strawberry milk had the second highest content of magnesium and calcium despite the fact that it is flavoured milk with average percentage content of 0.129 %. However, the milk brand that has the lowest concentration of calcium and magnesium ions was Jeju milk, having 0.085 %. The calcium and magnesium concentration of Seoul Milk was similar to Jeju’s percentage p ercentage with 0.086 %, only 0.001 percent higher. The average percentage difference between Low fat Maeil and Jeju is 0.056 %, which means that Jeju milk, contains 60 percent of calcium content to low fate Maeil’s. Maeil’s.
Using the bar chart, it is clear that we can rank the content of calcium and magnesium ions in different types of milk. Low fat Maeil and had the most
18
and secondly most abundant substances. Next is followed by Maeil Banana, Hershey
milk. Chocolate, No fat Maeil, Original Maeil,
Table 3: Mass of Calcium and Magnesium Ma gnesium ions in different types of milk Type of milk
No fat Maeil
Low fat Maeil
Original Maeil
Seoul
Jeju
Strawberry
Banana
Hershey Chocolate
Mass of Calcium 3 (mg/100 cm ) 108.1 100.8 93.5 149.4 110.9 139.3 92.5
Mean mass of calcium 3 (mg/100 cm ) 100.8
132.2
95.6
Mass of Magnesium 3 (mg/100 cm ) 6.1 5.7 5.3 8.5 6.3 7.9 5.3
99.9
5.7
94.4
5.4
93.5
81.3
5.3
65.2
3.9
85.2
4.8
85.2
80.9
4.8
82.5
4.7
75.1
4.3
126.5
121.6
7.2
111.8
6.3
126.5
7.2
107.2
106.9
6.1
103.6
5.9
110.0
6.2
105.4
103.9
6.0
104.5
5.9
101.7
5.8
Mean mass of Magnesium 3 (mg/100 cm ) 5.7
7.6
5.5
4.7
4.6
6.9
6.1
5.9
19
Average calcium and magnesium content in eight brands of milk were found: Calcium:
Magnesium:
=
=
3
= 102.90 mg per 100 cm .
5.88 mg per 100 cm3.
Referring back to Recommending Daily Allowance , 1 liter of milk has to be consumed in order to gain1000 mg of calcium for teenagers and 1.2 liter of milk for adults. Relating the analysis to dailymilk.co.uk, the skimmed, or no fat milk did not contain more calcium than the semi-skimmed, or low fat milk. In fact, it had less calcium content than low fat milk. Also, the calcium a nd magnesium concentration difference between low fat milk and no fat Maeil was big, about 31.4 mg while the concentration difference between low fat and original was small, about 4.8 mg. In comparison co mparison to the statement on the dailymilk website, the difference in c alcium between semi-skimmed and skimmed was about 10 times greater, while the no fat Maeil and original milk had a 29
difference in line with expectations. Such a big gap between the experimental work and dailymilk’s statement could be interpreted in two ways. First, the statement from the website is based on British milk. Thus, since Korean dairy companies produced the milk samples, its calcium content would have been different from Britain’ Britain’s milk. This is supported by the fact that the calcium content of no fat, low fat and original maeil varies far more than stated by the dailymilk.
29 According
3
to dailymilk.or.uk., the estimated calcium content per 100 cm were: Skimmed =22 mg Semi-skimmed = 20mg Plain = 18mg 20
When the content of calcium and magnesium was found, I realized that the experimental results and the claims from the milk carton had an anomaly. As a result, the comparison between the experimental value and the claims had been measured.
Type of milk
No fat Maeil Low fat Maeil Original Maeil Seoul Jeju Strawberry Banana Hershey Chocolate
Table 4: Theoretical and Practical Data Table Theoretical Experimental Theoretical – Theoretical – value mean value experimental 3 3 (mg/100 cm ) (mg/100 cm ) value 220.0 100.8 119.2 220.0 132.2 97.8 100.0 95.6 4.4 100.0 81.3 18.7 90.0 80.9 9.1 72.5 121.6 -49.1 76.6 106.9 -30.3 77.1 103.9 -26.8
Theoretical value of milk was gained from the calcium claims in its milk carton. But the chocolate drink and Maeil banana had calcium content of one carton so I had to 3
calculate its content per 100 cm . 3
It is claimed that Hershey Chocolate drink contains 180 mg (=0.18g) per 235cm . 3
So calcium content (g) per 100cm is: 0.18:235= x1: 100 235x1= 18 X1= 18/235 X1=0.076596 grams
3
For Maeil banana milk, the calcium content was claimed to be 185 mg per 240 cm . 0.185: 240 = x2: 100
21
240x2 = 18.50 X2=
= 0.0771
X2= 0.0771 grams
Theoretical value vs. Experimental mean value of calcium content in milk type 250 200 150 100 50 0
Theoretical value Experimental mean value
Graph 2: Theoretical value vs. Experimental value of calcium content in milk types types The most accurate brand of milk was Original Maeil, which had 4.4 milligrams 3
per 100 cm subtracted from the published values to the average experimental result. The second most accurate milk type was Jeju milk. In fact, the theoretical content of calcium 3
had more 9.1 milligrams per 100 cm than its average experimental value. The least accurate milk brand was Maeil strawberry milk. Maeil compan y claimed that it contained 3
72.5 mg in 100 cm but according to my experiment, the result came out as 112.6 mg which is 40.1 mg more than the theoretical value. 3
Similarly, No fat Maeil had 119.2 milligrams less calcium per 100 cm . Although Maeil Company claimed that it had same calcium content as low fat. No fat Maeil had 31.4 mg lower content than low fat fat Maeil. There was an interesting trend among the
22
flavored milks: Strawberry, Maeil Banana and Hershey chocolate, the experimental average data had about 35.4 mg more calcium content than its published data.
Evaluation Having determined the accuracy of the claims on the cartons and content of calcium and magnesium in each milk type, the reliability of the data collected will be discussed. In addition, random error and systematic error will be measured to find total error in the experiment.
Validity of Sources: Eriochrome Black T indicator was unable to detect the content of magnesium and calcium with: 2,2',2'',2'''-(Ethane-1,2-diyldinitrilo) tetraacetic acid(EDTA) acid(EDTA) titration separately. In other words, since EBT indicator functions to illustrate the content of calcium and magnesium ions in 10 ml of milk, another source were used to calculate each calcium and magnesium ions through titration. To some extent, the source was not reliable, because although the approximate calcium and magnesium content in milk was published by United States Department of Agriculture, the website was temporarily down. 30
The powerpoint resource largely influenced the method and procedures and the resource was used without knowing the validity of the source or the date it was created. One document was from a prominent university: University of Canterbury, New
30 Caudill,
D., Nichols, E and Vautier K. (no date). Real World: Detmerination of Calcium in Milk. Available: Milk. Available: http://www.google.co.kr/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&c ad=rja&ved=0CCYQFjAA&url=http%3A%2F%2Fstudents.ycp.edu%2F~dcaudill%2 FReal%2520World%2520Powerpoint.pptx&ei=ErRWUtyJM FReal%2520World%2520Powerp oint.pptx&ei=ErRWUtyJM8WikwXwxoGgB. 8WikwXwxoGgB. Last accessed 15th May 2013. 23
31
Zealand has plans for EDTA titration similar to those of the powerpoint. For example, in 3
the Canterbury document, it states, “pipette “pipette 10 cm of: 2,2',2'',2'''-(Ethane-1,2diyldinitrilo) tetraacetic acid sample acid sample solution with 10 ml of Ammonium chloride buffer (pH 10.5)” 10.5)”. 3
Moreover, 1 cm of Eriochrome Black indicator is suggested to be added. This implies that the powerpoint used to design my m y method is largely reliable. Lastly, I consulted a number of books and websites. I assumed that these sources were all reliable. This was because the books were clearly marked with the author ’s name, the date of publication and when the information given in the book was compared to the chemistry IB textbooks they were consistent. The websites also b y in large agreed with the books I had consulted. The manufacturer ’s claims are highly credible since these companies a re well known and highly respected throughout Korea for producing healthy and nutritious milk through numerous procedures. For instance, Maeil milks were produced through drying, comminuting, mixture and granules.
Random error has occurred using four types t ypes of equipment in the experiment. ex periment. 3
3
First is 10 cm measuring cylinder that measured 10 cm of milk sample. Its uncertainty is . Its error percentage is:
31 University
of Canterbury. (no date ). Determination of Total Calcium and Magnesium Ion Concentration. Concentration. Available: Available: http://www.chemteach.ac.nz/investigations/documents/ http://www.chemteach.ac.nz/i nvestigations/documents/magnesium_calcium.pdf. magnesium_calcium.pdf. Last accessed 27th Sept 2013. 24
3
3
Next is the 25 cm measuring cylinder that was used to measure 16.67cm of ammonium buffer solution. Its uncertainty is . The error percentage is:
Moreover, five drops of EBT indicator was put using a dropping pipette. The pipette had an uncertainty of The error percentage is:
I measured random error percentage by dividing 0. 10 (uncertainty for change in EDTA volume) over change in EDTA volume and multiplying by 10. E.g. No Fat Maeil:
Lastly, the burette in EDTA volume had an uncertainty of
of burette used to titrate EDTA volume.
25
Table 5: Random error Table
)
Random percentage error of each milk type is found by adding the average uncertainty percentage in table 2 and four other percentage errors found above. E.g. No fat Maeil 0.91 % + 1% + 1% + 10% = 12.91%
Table 6: Random percentage error
26
Type of milk Random % error (%) No fat Maeil 12.91 Low fat Maeil 12.70 Original Maeil 12.96 Seoul 13.13 Jeju 13.14 Strawberry 12.76 Maeil Banana 12.86 Hershey Chocolate 12.88 The average random % error is:
=12.92 %
By comparing my values to the literature values and hence determining the percentage error, I will be able to find the systematic error. error. Again, the assumption is that the ratio of ma gnesium to calcium is 11.2: 118.2. For example, No fat Maeil’s literature value is the calcium and magnesium content mentioned on the milk carton. Since the milk carton only gives calcium content in the milk which is 22 mg per 100 grams, the magnesium content have to be calculated based on the assumption mentioned above. Magnesium content (mg):
= 13.81
Thus, the literature value of magnesium and calcium content is: 13.81 + 220 =233.81 mg = 0.23381g Literature value percentage:
Experimental percentage value is found similarly: e.g. No fat Maeil 100.8 +5.7 =106.5mg = 0.1065 g
27
Systematic % error:
e.g. No fat Maeil
54.49 %
Table 7: Systematic Percentage Error Type of milk
Literature value
Average Experimental content value
Systematic % Error
No fat Maeil Low fat Maeil Original Maeil Seoul Jeju Strawb Strawberr erry y Banana Hershey Chocolate
0.234 0.234 0.109 0.109 0.098 0.079 0.079 0.083 0.084
0.1065 0.1398 0.1011 0.0860 0.0855 0.1285 0.1285 0.1130 0.1098
54.49 40.26 7.25 21.10 12.76 -63.04 -63.04 -36.15 -30.71
28
Percentage Error (%) 70 60 50 40 30 Systematic % Error 20
Random % Error
10 0
Graph 3: Percentage error (%) As the table suggests, the systematic percentage errors are high. Because the flavored milk had negative values, they are converted into absolute values to compare their values with other types of milk. There should have been an error in Calcium content of Maeil strawberry, Maeil banana milk and Hershey He rshey Chocolate drink milk (see table 4). It is said that th at the flavored milk drinkers did not have a significantly higher intake of calcium or other nutrients such 33
as phosphorous, magnesium, or potassium than those who just drank plain milk. Thus, the analyzed data showing that strawberry, Hershey chocolate, and banana milk have high content of calcium.
33 Jamie
Oliver's food Revolution. (no date). The Hard Facts about Flavored Milk. Available: http://www.jamieoliver.com http://www.jamieoliver.com/us/foundation/jamies-food/us/foundation/jamies-foodrevolution/__cms/uploads/JOFR_milkfactsheet_6.3.pdf. revolution/__cms/uploads/JOFR_milkfactsheet_6.3.pdf. Last accessed 21st Aug 2013. 29
Adding percentage errors for all eight milk types and then dividing it by eight find the average percentage error of eight types of milk.
= 33.22 %
Total percentage error for this experiment is: 33.22 + 12.92 % = 46.14% The random error affects largely the percentage error, as it is ¼ of the total percentage error. Yet, the major course of error is systematic. Taking this into account, I will now evaluate the weaknesses in the experiment and find some ways to improve that could reduce total percentage error.
It is suspected that systematic error is caused when I c arried the titration swiftly. In other words, I titrated the EDTA solution with flow. Therefore, there is a strong risk that I continued to add EDTA even after the end point was met. To reduce the accuracy of the experiment, I will titrate EDTA drop by d rop to accurately detect the end-point.
Milk samples’ expiration dates also dates also varied. Some of the milk samples were used beyond their expiration dates. If they are over those dates, the content of calcium would have decreased. . The milk samples should all have been before the expiration dates. Ideally, it would be preferable to have all the different types of milk produced on the same date or with the same expiration date to keep the calcium and magnesium content relative to prevent another variable.
30
The fact that the equipment was not cleaned may have affected the accuracy of 34
the experiment since fat content in milk makes the mixture oily. Thus, in order to improve, I will clean the apparatus using the soap and water after every trial.
The pH difference in every experiment varied from 2.00 to 2.30. As the units of data are in milligrams, even the decimal pH values v alues would affect the accuracy accurac y of the results significantly. As a result, I will make sure the pH change is constant in every trial. It may be difficult to measure the pH exactly ex actly the same in two significant figures like 2.15 but the pH difference should be constant to one decimal place. It would be preferable to put pH meter while titrating so that I could detect the pH difference. difference. But the titration must be carried out slowly in case the EDTA solution damages the pH meter.
There are three ways to reduce random rand om percentage error. First, when I add drops of EBT indicator using the dropping pipette, the number of drops should be carefully monitored.. In some trials, 6 or 7 drops of EBT indicator were added accidently accidentl y to the solution. Of course, as the milk sample utilized is so small (10 ml), adding a drop or two would have given different results. In addition, I will use small burette, as I know from the results that the average 3
change in EDTA to titrate 10 ml of milk sample is about 10 cm . It will be preferable to 3
use 15 cm burette to titrate.
34 Engels,
D. (no date). Experiment 36: Calcium content of Milk. Available: http://pvhs.fms.k12.nm.us/teachers/dengels/genchem_p http://pvhs.fms.k12.nm.us/teachers/dengels/genchem_ppts/Chapter%2012%20St pts/Chapter%2012%20St oich/Exp%2036%20Calcium%20content%20of%20milk.pdf. oich/Exp%2036%20Calcium%2 0content%20of%20milk.pdf. Last accessed 19th Mar 2013. 31
Lastly, in order to detect pure calcium and magnesium values separately from titration, the patton-reeder indicator should be used.
32
Conclusion Referring back to the research question, “An “An investigation into differing quantities of Calcium and Magnesium ions in eight types of milk produced in Korea,” Korea,” it can be concluded that there is a relatively significant difference in calcium and magnesium ions in different types of milk. To be more specific, spe cific, Low Fat Maeil milk had the highest h ighest concentration of calcium and magnesium while Jeju milk had the lowest. Also, the accuracy of the claims on each milk varied. Original Maeil milk was most accurate while no fat Maeil had the most inaccurate claim. Overall, milk contained a high quantity of 3
3
calcium (102.9mg/100 cm ) and magnesium (5.88mg/100 cm ). However, the massive total percentage error (46.14%) has to be taken account, which queries the accuracy of the results. In order to achieve recommended d aily allowance of milk, 1 liter of milk has to be consumed for teenagers and 1.2 liter of milk for adults. There are two questions that are unresolved. First is “What would have caused the flavored milk to have significantly more calcium content than was publicized?” publicized?” Second, “Why did the flavored milk have more calcium than some of the plain milk according to my results?” results?” To investigate further on this topic, the equipment each company uses in the factory to produce milk could be compared to correlate its accuracy. Moreover, the different ions’ content of milk could be measured using Atomic Absorption Absorption Spectroscopy, which is more accurate and is able to detect more than two metals. To go into greater depth, the data from AAS and EDTA titration could be compared and evaluated to show each method’s advantages advantages and disadvantages.
33
Appendix Appendix 1: Metal ions and their minimum pH Basic concepts of Analytical Chemistry pg. 68
34
Appendix 2: Pictures of Experiment
35
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