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Spectrophotometric Determination of Fe2+ (Beer's Law)

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Homework Statement
I need to determine the % by mass of iron for an experiment
Homework Equations
y=mx+b, and stoich
I am having troubles with a question I have to do for my chem pre-lab. The question is:
The following intercept and slope were obtained for a Beer’s Law plot of Absorbance versus concentration (mg Fe2+/L).
Slope = 0.2200 L/mg Fe2+
Intercept = 0.004
Calculate the percent (by mass) of iron in the unknown sample given the following mass and absorbance, assume the experimental data is obtained using the same procedure as outlined in the experiment.
Mass sample = 0.1097g
Absorbance = 0.252
I have attached what the procedure is. I kind of understand how to get the concentration using the intercept, slope, and absorbance. But, once I get the concentration I don't know what volume to use to calculate the moles to get to the amount of grams. I had used 0.01L for my volume and did not get the correct answer. Also, I tried to use the different concentrations and volumes from step 8 through 12 but still did not get the correct answer. If someone could explain this it would be very much appreciated
IMG_7879.JPG IMG_3256.JPG
 

mjc123

Science Advisor
811
367
You made up a solution containing the given mass in 100 mL. You then diluted this twice, and used the last solution for spectroscopy.
What is the relation of the concentration in the last solution to that in the first?
What concentration did you obtain from the spectroscopic measurement?
What is the concentration of the initial solution?
How much iron is in this solution?
 

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