Paper , Order, or Assignment Requirements

In this Case assignment, you will determine the spectroscopy of unknowns at:
http://amrita.vlab.co.in/index.php?sub=2&brch=190&sim=338&cnt=1 login is required to complete the assignment.

Use the prelab tutorials and resources in your Module 4 Playlist

Once you have set up your free account, please follow the procedure with the following additional instructions:

-Determination of Molar Absorption Coefficient-

1. Tabulate absorbance values for each compound between 350 to 700 nm in 50 nm increments
2. Plot the absorbance using Microsoft Excel or graph paper,
3. In Excel, use fitting software using polynomial fitting trend line with 6th order (or higher) fitting:
a. Click on a data point with your mouse to select the series
b. Right click, and select “Add trendline” from the drop down menu
c. Select “polynomial” and enter “6” in the “order” box
4. If not using Excel, plot the points on graph paper and use your eye to estimate a smooth curve that passes through all of the points.
5. All plots for each compound may be on the same graph, but must be distinguishable by color or other clearly distinguishable line or symbol characteristic.
6. Estimate the absorbance maximum at the wavelength from the curve.
a. This wavelength is specific for each compound should be the wavelength used for the absorbance measurements to determine concentration.
7. Make sure graphs have
a. Title
b. Axes labels
c. Legend (if there are multiple plots)

-Determination of unknown concentrations-

In addition to the calculations of molar absorptivity and concentration, you will also determine these values graphically.

1. For each compound, measure the absorbance for at least three different concentrations at its maximum absorbance wavelength.
2. Plot the absorbance versus concentration graph using Microsoft Excel or on graph paper.
3. Use a linear fitting trend line (in Excel), or use a straight ruler (graph paper) to manually draw a straight line that minimizes the distance from all of the points. To get a better perspective of whether your line is a best fit, view the graphed points along the line, edge on with your eye almost horizontal with the paper.
4. In addition to calculating the concentration of the unknown using the molar absorption coefficient, estimate the concentration of the unknown from your graph.

***Assignment Expectations****
Accomplish the exercises “Determination of Molar Absorption Coefficient” and “Determination of unknown concentrations” by following the virtual laboratory guide in the following order:

1. Read the background for the Lab by selecting the “Theory” tab.
2. Review the “Procedure.”
3. Test your understanding of the procedure and the required background using the “Self Assessment” tab.
4. Continue to the “Simulation” to complete the laboratory procedure. Record your results as you complete your simulation.
5. Complete the “Assignment” tab for each exercise. Be sure to complete the steps above in addition to the Assignment posted on the Amrita Lab.