Lab Report 7 PDF

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chemistry lab report # 7...

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Analysis of Cereal

Introduction The goal of this lab was determine the iron content of the given cereal and iron tablet to analyze if the iron present and the iron said to be present were the same amounts. The extraction of iron in both substances was done with either magnets and acids and then the substances’ absorbances were measured by using spectrophotometry. The results were compared to the concentration by calculating the calibrations and plotting them on a graph.

Experimental For the cereal extraction, the first part of the experiment, measure 32 grams of cereal into a 600mL beaker by using a top loading balance then transfer it to a bag and crush the cereal thoroughly. 30 grams of the crushed cereal was taken and added to a clean 600mL beaker with a magnet and 250mL of DI water. The solution was placed a stirring for 10 minutes before the magnet was removed and placed into another 600mL beaker containing 50 mL of 1.0 M HNO3 for 5-10 minutes on a heating plate. The magnet was then placed again in the slurry and the process of extraction repeated 2 more times. The HNO3, solution is then poured into a 100.00 mL volumetric flask. After rinsing the magnet three times with 10 mL of 1.0 M HNO, the three washes are also poured into the volumetric flask. 100.00mL of .10 M KSCN was prepared in another flask by using 1.0 M HNO3 as the solvent. 1.00 mL of the cereal solution was pipetted into 250 mL of the KSCN. The absorbance is then measured with the spectrophotometer.

For the iron tablet extraction, the second part of the experiment, an iron tablet and 20 mL of 5 M HNO3 was placed into a 25mL flash and heated on a hot plate. After 10 minutes, the tablet was crushed and heated for another 10 minutes. The solution is then decanted into a 100 mL volumetric flask. Wash the flask 4 times with 15 mL of DI water and add to the flask then fill the flask up to the line. Mix the solution then filter using gravity filtration. Pipette 1 mL of the solution into a 10mL volumetric flask and fill up to the line. 100.00mL of .10 M KSCN was prepared in another flask by using 1.0 M HNO3 as the solvent. 1.00 mL of the iron tablet solution was pipetted into 250 mL of the KSCN. The absorbance is then measured with the spectrophotometer.

For the preparation of the calibration curve, the third part of the experiment, 2 solutions were prepared: 100 mL of 1.0 x 10-3  MFE(NO3)3 and 100 mL of Fe(NO3)3 x 9 H2O. Pour the KSCN solution into a 250 mL beaker and add 1.0 mL of the iron nitrate solution. Using a clean cuvette, measure the absorbance at 480 nm of the 1.0 M HNO3 solution. Rinse the cuvette 3 times with the first solution and pour each wash back into the solution. 1.0 mL of the iron nitrate was added and mixed, then the cuvette was washed 3 times with this solution and measured with the spectrophotometer. The steps were repeated until a total of 10 mL had been added. The concentrations were calculated using the given formula and plotted onto a calibration curve with the absorbances on the vertical axis and the concentration on the horizontal axis.

Results and Calculations (combined section, 4 points):

Calibration Curve Volume of Iron Nitrate (L)

Absorbance (A) at

Iron Concentration (M)

480nm 0.001

0.074

9.90 x 10-6

0.002

0.132

1.96 x 10-5

0.003

0.200

2.91 x 10-5 

0.004

0.267

3.85 x 10-5 

0.005

0.334

4.76 x 10-5 

0.006

0.390

5.66 x 10-5 

0.007

0.446

6.54 x 10-5 

0.008

0.504

7.41 x 10-5 

0.009

0.560

8.26 x 10-5 

0.010

0.614

9.09 x 10-5 

Concentration Calculation (1.0 x 10-3  mol/L x .001 L)/.101L = 9.90 x 10-6 

Cereal Extraction y = 0.0604x + .0802 line of best fit 0.159 = 0.0604x + .0802 x= 1.30 (10-5  )M

Iron Content Calculation 1.30 (10-5  ) M  x 100 =1.30 (10-3  ) mol/L x 0.101L = .0001313molFe x 55.85g/molFe = .007333gFe = 7.333 mg Fe

Iron Tablet Extraction y = 0.0604x + .0802 line of best fit

0.506 = 0.0604x + .0802 x = 7.05(10-5  )M

Iron Tablet Iron Content Calculation 7.05(10-5) M  x 1000 =7.05 (10-2) mol/L x 0.101L = .00712molFe x 55.85g/molFe = 0.3977gFe = 397.7 mg Fe

Discussion: The RDA for iron stated by the National Institute of Health is between 8-18 mg for an adult. 1 The cereal as calculated to have about 7.333mg of iron which is almost the recommended amount whereas the iron tablet contained about 398mg of iron. The iron tablet may be recommended for people with diseases which cause them to have a lack of iron in their bloodstream such as anemia. With the average RDA being 13mg, 30g of cereal contains 56% of the average RDA and almost meets just the minimum RDA. The iron tablet contains 2843% of the average RDA of iron. Error in this experiment could have resulted from many factors with the largest source of error being compounded by the small errors. One source could be from the accuracy of measurements during the transferring of liquids. There could also be error in the calculations or the solution itself which skews the entire calculation. which again skews the calculations such as if too much solvent was used. A source of error could have been the incorrect usage of the calibration curve, which may have been calibrated differently depending on the spectrophotometer used which then induces systematic error. The form of iron present in

1

https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/

the cereal was pure iron Fe but the iron present in the tablet was ferrous sulfate FeSO4. The body uses dietary iron in the Fe2+  form once an enzyme has reduced it from the Fe3+  form. The ferrous form of iron is absorbed easier by the body, because it contains more elemental iron and is therefore the preferred iron supplement option. Ferrous sulfate is one of these forms hence the tablet is easier on the stomach and the recommended dosage for that is 325 mg which is much closer to the value that was calculated 397.7 mg. Even though the body can take both forms, it is more efficient to gain the iron in a supplement.

Conclusion In the experiment, the concentration of iron and the total amount of iron in each solution could be determined by measuring the absorbance of different solutions. The iron from the tablet and the cereal could be dissolved and calculated which demonstrates that both sources contained a high percentage of iron compared to the recommended allowance. One can get the recommended daily dosage by simply eating cereal as cereal as well as a variety of other foods contain iron but if one’s body cannot process iron as others may, he or she may take iron supplements in order to continue having the RDA of iron.

Concept Q In a typed paragraph, explain how a calibration curve was used in this experiment to determine the amount of iron in the cereal and tablet. Include in your discussion an explanation of the Beers-Lambert Law.

To compare the relationship between the concentration and the absorbance of iron, the calibration curve helped to visualize the comparison as well as predict absorbances of higher concentrations. The data collected and plotted were due to the standardization of the concentration of the iron solution and the measuring of the absorbance through the spectrophotometer. The Beers-Lambert Law defines the relationship between the absorbance of light and the concentration of the substance as directly proportional so that for each absorbance that has been measured at a specific wavelength, there exists a corresponding concentration; hence the existence of a calibration curve and its defined trend line....