Applying Lab Learning and Techniques to Real-Life Application: Quantification of Iron in Whole Grain Cereal

Applying Lab Learning and Techniques to Real-Life Application: Quantification of Iron in Whole Grain Cereal

Yaning Guo and Zihao Cai (partner)

Submitted to: Dong Guo

Chem 1045, Experiment 12, 30 October, 2016

Honor Code Signiture: Yaning Guo

Abstract

The objective of Experiment 12 is to determine the concentration of iron in whole grain cereal. Students will use magnetic stir bar to collect iron flakes of Total cereal because elemental iron is ferromagnetic. Students will dissolve iron flakes in HCl solution and measure the absorption of iron in the cereal sample by using an Agilent Atomic Absorption (AA) instrument. As a result, students will make a calibration curves according to the data to determine the concentration of iron in the cereal sample.

I. Introduction.

Most foods are now labeled accordingly to give the relevant information, but some information on the packet are are misleading. The packet label also indicates that Total cereal also contains 100% of the daily recommended intake of iron, and any label indicates iron present in a reduced form. Therefore, in this experiment we are trying to determine the concentration of iron in whole grain cereal. Students will take a sample of Total cereal and extract and determine the amount of iron metal present. Having extracted the Fe metal, students will dissolve it in HCl solution. Then, students will combine 2mL of the diluted iron solution with 2 drops of 6.0M HCl, 0.50mL 10% Hydoxylamine-HCl, 6 drops of 2.0M Sodium acetate solution, and 1mL of 0.1% 2,2 Dipyridyl solutions and perform a quantitative analysis by using an Agilent Atomic Absorption (AA) instrument.

II. Experimental.

Procedure:

Firstly, take around 10gm of Total cereal and record the exact mass. Grind the cereal to a fine powder by an electric grinder. Transfer the cereal sample to a 150mL beaker and add enough water to make a mobile slurry. Stir the slurry for 10min by the magnetic stir plate and a magnetic stir bar. The iron can be collected on the stir bar as small black flakes. Pour off the cereal mush to the waste container. Remove the remaining stir bar, using a stir bar retriever. Then, wash the remaining cereal mush from the stir bar using a DI wash bottle. Rinse the dirty beaker with DI water and dispose it into waste container. Put the stir bar with iron flakes into a test tube and cover with 6mL 6.0M HCl(aq). Put the test tube into a hot water bath and boil for 10min to increase dissolving the Fe. When H2 gas ceases to evolve, the dissolution is complete. The result solution is a pale green Fe(Cl)2(aq). Transfer the contents into a 100mL volumetric flask and add 100mL DI water. Pipet 2mL diluted Fe(Cl)2 solution into a 10mL volumetric flask. Add 2 drops of 6.0M HCl, 0.50mL 10% hydroxylamine-HCl, 6drops of 2.0M sodium acetate, and 1.0mL 0.1% 2,2-dipyridyl solution. Dilute with DI water to the 10mL mark. Use the AA instrument to measure the absorbance at 522nm of six Fe standard solutions (1,2,4,5,and 8ppm). Use these samples to generate a calibration curve. Finally, measure the absorbance at 522nm of the diluted cereal sample prepared above using the AA instrument.

Data:

Table 1 – Atomic Absorption data for standards and sample

[pic 1]

Observation:

After stirring the slurry for 10min, we can see small black flakes on the stir bar, which is iron we collected. After putting the test tube with iron flakes and HCl(aq) into a hot water bath and boiling for 10min, we can see iron is dissolving, bubbles in the test tube, and the solution becomes a green-yellow solution, which is Fe(Cl)2(aq).

III. Results and Discussion.

Results and Discussion:

1. In this experiment, we first take 10.06g cereal and grind it to a fine powder. Then, we add enough water to make mobile slurry. We use the magnetic stir plate and magnetic stir bar to collect iron flakes. As a result, we extracted iron from our cereal sample. We put the test tube with iron flakes and HCl(aq) in a hot water bath and boil it to get Fe(Cl)2 solution.The reaction equation: Fe+2HCl=Fe(Cl)2+H2. Then, we combine 2mL of the diluted iron solution with 2 drops of 6.0M HCl, 0.50mL 10% Hydoxylamine-HCl, 6 drops of 2.0M Sodium acetate solution, and 1mL of 0.1% 2,2 Dipyridyl solutions and perform a quantitative analysis by using an Agilent Atomic Absorption (AA) instrument.By using the Agilent Atomic Absorption (AA) instrument, we measure the absorbance at 522nm of six Fe standard solutions (1,2,4,5,8ppm and sample). By pluging in the data in Excel, we get the calibration curve of absorption and concentration. According to the linear equation of the calibration curve, we can calculate the concentration of iron in cereal sample.

2. The iron measured in the cereal in the laboratory experiment did not compare to that provided on the consumer label. The label indicates that Total cereal also contains 100% of the daily recommended intake of iron. The daily intake of iron for an adult is 17.0-20.5mg/day. According to the calculation, 10.06g cereal contains 0.0013g=1.3mg iron. The serving size ¾ cup is 30g, so it contains 3.9mg iron, which is less than 17mg. Therefore, it did not compare to that provided on the consumer label.

3.It was important to use volumetric glassware to prepare the sample because volumetric glassware are used for precise dilutions and preparation of standard solutions. In this experiment, we have to mix multiple solutions and dilute them to 100mL. Therefore, we use a precise mearsuring tool--volumetric glassware to prepare the sample.

Sample Calculations:

According to the calibration curve, we get the linear function y=0.0563x+0.004.

The absorption of our cereal sample is 0.0375, 0.0375=0.0563x+0.004, so x=0.60.

...