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

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

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.

Part 1. Preparation of calibration curve Pipet 1.00, 2.00, 3.00, 4.00, and 5.00 ml of standard Fe solution into 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

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

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 concentration of Fe+2 complex (mg/ml) Absorbance 1 .001 .15 2

calibration curve Prepare calibration curve by plotting absorbance vs concentration

Part B: Determination of Fe+3 complex Create Fe +2 ion 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

Part B: Determination of Fe+3 complex Convert Fe +2 ion to Fe+3 complex Pipet 1ml of Fe +2 ion from the erlenmeyer flask into 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

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 absorbance at 510 nm Using the absorbance determine concentration of Fe+2 complex (mg/ml) by extrapolating from your graph