DETERMINATION OF IRON SPECTROPHOTOMETRICALLY WITH 1,10-PHENANTHROLINE

OBJECTIVES:

1. The student will analyze an ore spectrophotometrically.
2. The student will use the calibration curve method of analysis.
3. The student will use hydroxylamine hydrochloride as a reducing agent.
4. This method depends on the proper buffering of the pH.
5. This method also depends on the fact that all of the sample is dissolved.
6. A known and unknown are treated alike.

PROCEDURE:

  1. Solutions that are prepared for you and in "squeeze" flasks:

a. 1,10 phenanthroline (0.1%): dissolve 0.25 gram in 250 ml of 50% ethanol.
b. Hydroxylamine hydrochloride: 10% aqueous solution.
c. Sodium acetate: saturated aqueous solution.

2. Solutions that each student should prepare:

FOR BOTH THE KNOWN AND THE UNKNOWN IRON SOLUTION, DISSOLVE THE IRON SAMPLE IN A 150 ML BEAKER ON A HOT PLATE UNDER THE HOOD. COVER THE BEAKER WITH A WATCH GLASS. QUANTITATIVELY TRANSFER THE SOLUTION TO A VOLUMETRIC FLASK.

a. Standard solution of Fe(III)(40 ppm): dissolve 0.04 g of iron wire in 10 mL of 1:1 HCl (crumple wire and cover with acid-heat may be needed) and 5 mL of concentrated HNO3 to oxidize all of the iron. Dilute to 500 mL. This solution contains a known ppm of iron. Calculate the value using your weight.

b. Solution of unknown ore. Take 0.1 gram of the iron ore sample. Add 10 mL of conc. HNO3 and 10 mL 1:1 HCl. Boil for 10 minutes (or until dissolved). Check to see if the sample is dissolved (no red particles). Dilute to 500 mL in a volumetric flask, after all of the sample is dissolved.

3. In 100 mL volumetric flasks prepare a series of standard solutions containing 1.00, 2.00, 3.00, 4.00, 5.00 6.00 and 8.00 mL of standard Fe(III) solution. (Use either a buret or a pipet to measure the standard solution). Add 10 mL of sodium acetate, 10 mL of hydroxylamine hydrochloride and 10 mL of 1,10 phenanthroline. Dilute to the mark with deionized water. Wait for 10 minutes. Measure the absorbance of the solution the day you make the dilution.. Make a plot using Excel and regressing the data. Discard obviously bad points.

4. In 100 mL volumetric flasks prepare a series of unknown solutions containing 1.00, 2.00, 2.50, 3.00, 4.00, and 5.00 mL of the unknown iron solution. Treat the unknowns the same as the knowns in step #3. If the solutions are more colored than the standard solutions you must use less unknown -- also if the unknowns are much less colored than the standards, you will need to use more unknown. Check with Dr. Sherren to see if your solutions are in the proper color range. All spectral measurements are made in 1 cm cells at 510 nm wavelength. All solutions must be read the day they are prepared. Better results are obtained if the standard curve and the unknown solutions are run on the same day.

5. Before making the first spectral measurement, you should receive instructions from Dr. Sherren on the use of the spectrophotometer.

6. Calculate the %Fe in the ore. Best results are obtained by calculating the best straight line on the computer. Excel does a nice job.

REF: page 858-860 of your text.

CAUTION:The iron ore should be dried on the day it is weighed.

This may mean re-drying the sample.

DO NOT OVER DRY THE SAMPLE!

SAFETY AND DISPOSAL INFORMATION: Dispose of all test solutions and precipitates in the "SPEC IRON EXPERIMENT WASTE" container.

CAUTION: Remember to treat all chemicals with respect.

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