1. Experiment 33: Colorimetric determination of 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
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

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

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

8. 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

9. 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

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