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Carleton University *

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Jan 9, 2024

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Fe: Spectrophotometric Determination of Iron Date submitted: 2022 By: Lab section: TA: Procedure: 1. 25.00 ml of a concentrated standard solution that contained 0.2500 g/L of iron were pipetted into a 500.00 ml volumetric flask. The solution was diluted up to the mark with distilled water and was mixed well as it was filled. 2. Six calibration standards of the diluted standard iron solution were prepared, containing 0.05 mg, 0.10 mg, 0.15 mg, 0.20 mg, 0.25 mg of iron. 3. 10.00 ml of an unknown iron sample was pipetted into a 250.00 ml volumetric flask and was diluted to the mark with distilled water while being mixed. 4. Two 25.00 ml aliquots of this were pipetted into two different 50.00 ml volumetric flasks. 5. 4.0 ml 10% hydrixykamine hydrochloride and 4.0 ml 0.3% ortho-phenanthroline were pipetted into each of the eight 50 ml volumetric flasks. 6. Each flask was diluted to the mark with distilled water after 10 minutes had passed. 7. The wavelength on the spectrophotometer was set to the value chosen. 8. 2/3 of a cuvette was filled with the blank solution and was zeroed in the spectrophotometer. 9. The cuvette was rinsed with the most dilute solution after emptying the blank solution from it. The absorbance was measured after the cuvette was filled to 2/3 with this solution. 10. After the solution was emptied, the same process was repeated and the absorbance of each solution was measured, in order of increasing levels of concentration. 11. The cuvette was rinsed with distilled water and subsequently rinsed with a small amount of the first unknown solution. The absorption of the first unknown was measured before the cuvette was rinsed with a small amount of the second unknown solution. The cuvette was then filled and the absorption of the second unknown was measured. Data and Observations: Concentration (mg/50mL) Absorbance 0 0.000 0.05 0.201 0.10 0.389 0.15 0.587 0.20 0.787 0.25 1.023 Unknown trial 1 0.674 Unknown trial 2 0.677

0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.2 0.4 0.6 0.8 1 1.2 f(x) = 4.04 x − 0.01 R² = 1 Iron: Spectrophotometric Concentration (Fe/50ml) Absorption Figure 1: Plot of Absorbance vs. Concentration of the standard iron solutions Calculations and Discussion: Calculating the concentration of the first unknown sample (in mg/50mL) y = 4.0406 x − 0.0072 0.674 = 4.40406 x − 0.0072 x = 0.15468 mg 50 mL Converting the concentration to mg/mL C 1 = x 50 C 1 = 0.15468 50 C 1 = 0.0030281 mg mL Calculating the average concentration of the two unknown samples C av = C 1 + C 2 2 C av = 0.0030281 + 0.0030417 2 C av = 0.0030349 mg mL

Calculating the dilution factor d = ( v f 1 v i 1 )( v f 2 v i 2 ) d = ( 250 10 )( 50 25 ) d = 50 x Calculating the concentration of iron in the undiluted unknown sample C ud = d ∗ C 1 ∗ g 1000 mg ∗ 1000 mL L C ud = 50 ∗ 0.0030281 mg mL ∗ g 1000 mg ∗ 1000 mL L C ud = 0.15141 g L Calculating the error of our value Error = experimental − actual actual × 100% Error = | 0.15141 − 0.1735 | 0.1735 × 100% Error = 12.732% Calculating the precision p = ( high − low average ) ∗ 1000 ppt p = ( 0.15468 − 0.15141 0.15304 ) ∗ 1000 ppt p = 21.367 ppt Extinction Coefficient ϵ = 11282 Conclusion:

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In this laboratory experiment, the concentration of iron from the unknown sample was calculated to be 0.15141 mg/mL, the actual value being 0.1735 producing an error of 12.732%. The relative spread was 21.367ppt. The extinction coefficient was calculated to be 11282 mol*cm. References: Archer, D.W., Burk, R.C., White, C.A., Wolff, P.A., Levac, S., Mesnic, N., Hunt, V., CHEM 1101 Chemistry for Engineers Lab Manual, Carleton University, 2021-2022 .