Instructor Information
JCE Classroom Activity: #66
A Magnetic Meal photo by J. J. Jacobsen, E. K. Jacobsen, J. Cunningham
In this Activity, students make slurries of cereal and water and use a magnetic wand to collect elemental iron filings that are present in some cereals. They determine the mass of iron collected and then calculate the “recommended daily allowance” in each cereal. An extension uses qualitative tests to confirm that the material collected is actually iron.
The average American’s diet includes 17 mg of iron per day, of which some 45% is supplied by the 700 metric tons of iron added to flour and cereal products annually, often in the form of Iron filings are collected from iron(II) sulfate (1). Some cereal manufacturers prefer to add particles of pure iron metal (called a cereal/water slurry using a elemental iron or reduced iron) because elemental iron is stable in storage and does not affect magnetic wand. the cereal’s flavor (2). The body’s stomach acid, HCl, can dissolve elemental iron. However, relatively little is dissolved during the short time a meal of cereal spends in the stomach. The iron must be dissolved, because the intestines can only absorb iron as either iron(II) or iron(III) ions (1). In 2002, the recommended daily allowances (RDAs) for iron changed when the National Academy of Sciences released new guidelines: 18 mg for women age 19–50 and 8 mg for men age 19–50 (3). Women have a higher RDA because a large amount of iron can be lost monthly during menstruation.
Integrating the Activity into Your Curriculum This Activity connects chemistry to an item that students probably see (and eat!) often. Many students will find it surprising that metallic filings are present in a food item. The Activity can lead to a discussion of why iron is/is not used in food items in this form. Instructors can also discuss biochemical issues—what happens to iron in the body, why iron is a crucial nutrient, and the definition of RDA. A Journal experiment presents a method to determine the quantity of iron in other foods using spectrophotometry (4). Two demonstrations using cereal are also in this issue (5).
About the Activity A “magnetic wand” is used in this Activity. It is a magnet encased in colored plastic with a handle attached to it. Other magnets could be used, but the wand allows students to easily stir the cereal/water mixture, while the colored plastic coating makes it easy to see any iron filings. Magnetic wands are sometimes available in teaching supply stores or with bingo game products (the wand is used to collect magnetic bingo chips). They are also available from science supply companies such as Educational Innovations (6). Cost is approximately $2–3. This Activity works best if students use fairly sensitive balances. Accurate comparisons between cereals can easily be made using a 0.001 g balance. Our tests gave 0.038 g of iron in two servings (60 g) of Total brand cereal, and 0.031 g of iron in Multi-Grain Cheerios brand cereal. Both are manufactured by General Mills, which tends to use elemental iron. Other cereals may contain oxidized forms of iron, and will not yield any iron filings. This issue is addressed in Question 3 on the Student Activity. The way iron is listed as an ingredient varies widely so it can be difficult to tell from the ingredients list which type of iron is included. Students should not eat or taste any of the food products used in this Activity. The cereal/water slurry may be poured down a running garbage disposal, but disposal down an ordinary drain may clog pipes. Instructors may wish to dispose of the mixture in a trash can. perforated
More Things To Try The filings with vinegar will turn a red-brown color, indicating the rusting of iron, 2Fe(s) + 3O2(g) → Fe2O3(s). The filings with 1M HCl will dissolve and produce a yellow solution, indicating 2Fe(s) + 6HCl(aq) → 2FeCl3(aq) + 3H2(g). FeCl3 in aqueous HCl solution is yellow. The vinegar test takes 12–24 h, the HCl test takes ∼48 h.
This Classroom Activity may be reproduced for use in the subscriber’s classroom.
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Background
Answers to Questions 1. Answers will vary. Data obtained during testing for two servings of Total brand cereal gave 0.038 g iron. The nutritional label states that one serving provides 100% of the RDA. This would give an RDA of 19 mg. 2. Answers will vary, depending on the values obtained for Question 1. 3. Some cereal manufacturers do not include iron in its elemental (strongly magnetic) form. They may include iron in an oxidized form such as iron(III) phosphate (2) or iron(II) sulfate (1), which are not as strongly magnetic. 4. Stomach acid is able to dissolve elemental iron to its ionic form, which can then be used by the body.
References, Additional Related Activities, and Demonstrations 1. 2. 3. 4. 5. 6.
Senozan N. M.; Christiano, M. P. Iron As Nutrient and Poison. J. Chem. Educ. 1997, 74, 1060–1063. Schmidt, Karen. Iron for Breakfast. Chem Matters 1994, October, pp 13–15. Daciuk, Janice. Striking a Balance with Iron. Cooking Light 2004, August, pp 52–61. Adams, Paul E. Determining Iron Content in Foods by Spectrophotometry. J. Chem. Educ. 1995, 72, 649–651. Jacobsen, Erica K.; Maynard, James. Iron in Breakfast Cereal. J. Chem. Educ. 2004, 81, 1544. Educational Innovations, order #M-510, 888/912–7474, http://www.teachersource.com (accessed Aug 2004). JCE Classroom Activities are edited by Erica K. Jacobsen and Julie Cunningham
www.JCE.DivCHED.org •
Vol. 81 No. 11 November 2004 •
Journal of Chemical Education
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JCE Classroom Activity: #66
Student Activity
A Magnetic Meal Cereal boxes often function as breakfast reading material. The panel of nutritional facts usually lists percentages for vitamins and minerals. Your cereal may offer “Vitamin A: 10% Daily Value” and “Iron: 60%”. Our body requires various quantities of these crucial nutrients to function properly. Iron plays a particularly important role. 60–70% of the human body’s iron is in hemoglobin, a protein in the blood that transports oxygen. Iron is present in hemoglobin in the form of Fe2⫹ ions. These ions form a loose covalent bond with oxygen as the hemoglobin picks up oxygen in the lungs; once the hemoglobin reaches tissues in need of oxygen, the bond breaks. Cereal manufacturers have a few choices for how they include iron in their product. In this Activity, you will determine how the makers of “Total” cereal offer you iron in your morning meal, and will investigate how much iron is contained in “Total” and in a second cereal. photo by J. J. Jacobsen, E. K. Jacobsen, J. Cunningham
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You will need: brand-name “Total” breakfast cereal, a second breakfast cereal, nutritional labels from the cereals, a nonmagnetic container to hold ∼4 cups (∼1 L), plastic zip-seal bag, rolling pin, balance (0.001 g or greater precision), water, measuring cup, spoon, dropper, clock or timer, coffee filter or filter paper, and magnetic wand. __1. Place a nonmagnetic container (∼4 cup capacity; ∼1 L) on a balance (0.001 g or greater precision). Tare the balance. Measure two serving sizes (∼60 g) of brand-name “Total” breakfast cereal into the container and record the final mass of the cereal. Be Safe! Do not __2. Pour the cereal into a plastic zip-seal bag. Close the bag, pushing as much air out of the bag as eat or taste any of possible. Use a rolling pin to crush the cereal into very small pieces. the food used in this __3. Pour the cereal back into the container from step 1. Add two cups (480 mL) of water. Stir the Activity. mixture thoroughly with a spoon. Allow the mixture to sit for 15–20 min. __4. Weigh a coffee filter or piece of filter paper and record the mass. __5. Use a magnetic wand to stir the cereal/water mixture gently for 2 min. After 2 min, remove the magnetic wand. Look closely at the wand surface. Besides cereal, what do you notice sticking to the wand? __6. Using a dropper and water, gently rinse only the brown cereal pieces from the wand. Wipe the remaining residue from the wand onto the coffee filter or piece of filter paper from step 4. What color is the remaining residue? __7. Repeat steps 5 and 6 until no noticeable residue is left on the magnetic wand after the cereal pieces are rinsed off. __8. Repeat steps 1–7 for a second breakfast cereal of your choice. __9. Allow the filters and residue to dry thoroughly. Weigh each filter with its residue and record the mass.
More Things To Try This Activity uses iron’s magnetism to extract it from cereal. Mixing the magnetic residue with chemicals that have a known reaction with iron can help to determine whether the residue is iron. Do your observations of the reactions between the residue and the chemicals below match what you would expect to see if the residue is iron? You will need: white household vinegar (5%), 1 M HCl, residue from the filter used in step 6 above, spatula, small beaker, two small watchglasses, dropper. __1. Use a spatula to scrape the residue from each of the filters used in step 6 above. Place one filter’s residue on a small watchglass and one filter’s residue in a small beaker. __2. Use a dropper to cover the residue on the small watchglass with a thin layer of white household vinegar (5%). __3. Use a dropper to cover the residue in the small beaker with 1 M HCl. Cover the beaker with a clean watchglass. __4. Let the watchglass and the covered beaker sit for 24–48 hours. Record your observations.
Questions 1. Calculate values for the recommended daily allowance (RDA) of the two cereals you tested using the data you obtained and the serving size and percentage daily value for iron listed on each cereal’s nutritional label. 2. The RDA for iron is 18 mg for women 19–50 years old and 8 mg for men of the same age range. How do your calculated RDA values from Question 1 compare to these values? 3. Some cereals, even though they list iron as an ingredient, will not yield any residue on the magnetic wand. What is a possible explanation for this? What is a different way that the manufacturers may have included iron? 4. The body is unable to use iron directly in its reduced metallic form. How might stomach acid (HCl) function to produce a usable form of iron for the body?
Information from the World Wide Web (accessed Aug 2004) Dietary Supplement Fact Sheet: Iron. http://ods.od.nih.gov/factsheets/cc/iron.html This Classroom Activity may be reproduced for use in the subscriber’s classroom.
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Journal of Chemical Education •
Vol. 81 No. 11 November 2004 •
www.JCE.DivCHED.org
