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Experiment 33: Colorimetric determination of iron

Experiment 33: Colorimetric determination of iron. PURPOSE To become aquainted with the principles of colorimetric analysis. THEORY. When mixed with phenanthroline , Fe 2+ ions reacts to form an orange red complex

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Experiment 33: Colorimetric determination of iron

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  1. Experiment 33: Colorimetric determinationof iron PURPOSE To become aquainted with the principles of colorimetric analysis.

  2. THEORY • When mixed with phenanthroline , Fe2+ions reacts to form an orange red complex • The color of the solution is directly proportional to the concentration of Fe3+ions present. The concentration of these ions can be determined by measuring the absorbance of a unknown Fe2+ complex solution and comparing it with the absorbance of a solution of known concentration. • Colorimeters measure the amount of light that is transmitted or absorbed by a solution. A description of how they work can be found in your text book • Fe3+(aq) needs to be reduced to Fe2+ by adding hydroxlyamine

  3. SAFETY PROCEDURES • Follow all instructions for using the equipment in this activity. • 2. Wear safety glasses and a laboratory coat for this experiment. • 3. Do not throw any waste down the sink.

  4. Part 1. Preparation of calibration curve • Pipet1.00, 2.00, 3.00, 4.00, and 5.00 ml of standard Fe solutioninto a 50 ml volumetric flasks 1 – 5 respectively • Add to each flask • 1ml of 1M ammonium acetate • 1ml of 10% hydroxylamine • 10 ml of .30% phenanthroline • Dilute the rest to 50 ml with water

  5. Part 1. Preparation of calibration curve • Mix well • Let sit for 40 minutes for the color to develop • Clean six cuvettes • Add water to one cuvette ½ way and calibrate spectrophotometer to 510 nm • Fill the other 5 cuvettes ½ way with a solution of increasing concentration • Record absorbance

  6. Part 1. calibration curve • graph concentration of Fe+2 complex (mg/ml) vs absorbance • Absorbance on y axis and concentration on x as seen on page 425

  7. calibration curve • Prepare calibration curve by plotting absorbance vs concentration

  8. Part B: Determination of Fe+3 complex • Weigh 0.1 g to 4 sig figs of Fe unknown into a 50 ml volumetric flasks • Add • 5 drop of 6 M sulfuric acid • Dilute the rest to 50 ml with water • Transfer to a 125 erlenmeyer flask Create Fe +2 ion

  9. Part B: Determination of Fe+3 complex • Pipet 1ml of Fe +2 ion from the erlenmeyer flaskinto three 50 ml volumetric flasks • Add to each flask • 1ml of 1M ammonium acetate • 1ml of 10% hydroxylamine • 10 ml of .30% phenanthroline • Dilute the rest to 50 ml with water Convert Fe +2 ion toFe+3 complex

  10. Part B: Determination of Fe+3 complex Mix well Let sit for 40 minutes for the color to develop • Clean 3 cuvettes • Fill the 3 cuvettes ½ way with each Fe+3 complex solution • Record absorbanceat 510 nm • Using the absorbance determine concentration of Fe+2 complex (mg/ml) by extrapolating from your graph

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