Spectrophotometric Determination of Fe2+ (Beer's Law)

In summary, the conversation is about a student having trouble with a question regarding the percent of iron in an unknown sample using Beer's Law. The procedure involves using the intercept, slope, and absorbance to calculate concentration, but the student is unsure about the volume to use for calculating moles. They also mention diluting a solution and using spectroscopy. The question asks about the relation between the concentration in the last solution and the initial solution, the concentration obtained from spectroscopy, and the amount of iron in the initial solution.
  • #1
fbeaker
1
0
Homework Statement
I need to determine the % by mass of iron for an experiment
Relevant 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
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  • #2
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?
 

FAQ: Spectrophotometric Determination of Fe2+ (Beer's Law)

What is spectrophotometric determination of Fe2+ (Beer's Law)?

Spectrophotometric determination of Fe2+ (Beer's Law) is a method used to measure the concentration of iron (II) ions in a solution. It is based on Beer's Law, which states that the absorbance of light is directly proportional to the concentration of the absorbing species in the solution.

What is the principle behind spectrophotometric determination of Fe2+ (Beer's Law)?

The principle behind spectrophotometric determination of Fe2+ (Beer's Law) is that iron (II) ions absorb light at a specific wavelength, and the amount of light absorbed is directly proportional to the concentration of iron (II) ions in the solution. This relationship is expressed mathematically as A = εbc, where A is the absorbance, ε is the molar absorptivity, b is the path length of the light through the solution, and c is the concentration of the absorbing species.

What are the requirements for performing spectrophotometric determination of Fe2+ (Beer's Law)?

The requirements for performing spectrophotometric determination of Fe2+ (Beer's Law) include a spectrophotometer, a series of standard solutions with known concentrations of iron (II) ions, a cuvette to hold the solution, and a light source. It is also important to ensure that the spectrophotometer is properly calibrated and that the solutions are free of any interfering substances.

What are the limitations of spectrophotometric determination of Fe2+ (Beer's Law)?

One limitation of spectrophotometric determination of Fe2+ (Beer's Law) is that it can only measure the concentration of iron (II) ions in a solution, and not other forms of iron. Additionally, the presence of other substances in the solution can interfere with the accuracy of the results. It is also important to note that Beer's Law assumes a linear relationship between absorbance and concentration, which may not always hold true.

How is spectrophotometric determination of Fe2+ (Beer's Law) used in scientific research?

Spectrophotometric determination of Fe2+ (Beer's Law) is commonly used in scientific research to measure the concentration of iron (II) ions in various samples. It is particularly useful in environmental studies, as iron (II) is a common pollutant in water and soil. It is also used in medical research to measure the levels of iron (II) in biological samples, such as blood or tissues. Additionally, this method can be used to monitor the progress of chemical reactions that involve the formation or consumption of iron (II) ions.

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