Iron in Water?

 

Over Spring break, your mother was bragging about the great job you did to determine the substances in the corroding barrels (remember back to the beginning of the semester?!).  Hearing this, your Aunt Betty and Aunt Joanie got very excited.  They live up on the iron range in Northern Michigan and have been wondering for some time, how much iron is in their tap water.  They figured that since you did such a great job with the corroding barrels, you wouldn't mind doing this lab for them. 

 

This week, you will determine the concentration of iron in your Aunts’ water using spectrophotometry, the method we explored last week.  By following the instructions given below and using a stock standard solution[1] of iron provided, you will prepare an orange-red solution (with only one wavelength of maximum absorbance!) that has a concentration of 3.00 parts per million.  With this start, you and your partner must develop a procedure to determine the iron concentration (in parts per million) in your Aunts’ water (yes, both Aunts’ water!). 

 

When you have figured out your procedure, find your lab instructor and get approval for that procedure.  You will then get the ok to begin the experiment. 

 

Prepare the 3.00 ppm iron solution in this way -

1.      Obtain 15-20 mL of standard iron solution in your graduated cylinder.  Rinse your 10 mL pipet with the solution.  Use your pipet to transfer 10.00 mL of iron solution to your 100 mL volumetric flask. 

2.      Use a clean graduated cylinder to transfer 10 mL of 10% hydroxylamine hydrochloride into the same volumetric flask.  Wait ten minutes.

3.      Use a clean graduated cylinder to transfer 10 mL of 10% sodium acetate solution to the same volumetric flask. 

4.      Add 20 drops of 1,10 ortho-phenanthroline to the same volumetric flask. 

5.      Dilute to the mark on the volumetric flask using distilled water. 

 

Prepare a lab report using our usual format. Be sure that all data are neatly organized in a table.  Your Aunts are very particular about data presentation, so we will be looking very carefully at your data presentation.  Be sure to give the concentration of the iron in their tap water in your conclusion and provide a brief explanation telling how you were able to determine it.  Go ahead and show off a bit by predicting the wavelength of light you believe will be absorbed by this orange-red solution.  Include your prediction in the conclusion as well. 

 

Keep in mind that Aunt Betty and Aunt Joanie are very particular and demanding.  They will expect you to give excellent results for this analysis.  Therefore, the grader will also be very particular about your results.  Half of your grade for this experiment will be determined by how close you are to the accepted value of iron in the original tap water.  The other half will be based on your write up.