Alex Aguilar
BEER’S LAW LAB
Create your own data tables and graphs on separate
piece of paper. Make sure partner's name are on
the paper
INTRODUCTION
1. Explore the Beer’s Law screen for a few minutes. Try to figure out what all of
the controls show and do.
2. How does Concentration affect how much light is absorbed and transmitted
through the solution?
Concentration affects how much light is absorbed and transmitted through and transmitted
through the solution because as it increases absorbance also increases and light transmitted
decreases.
INVESTIGATING ABSORPTION
1.
AND
CONCENTRATION
Predict what a graph of absorbance versus concentration would look like.
Sketch your prediction.
Prediction
Can’t edit graph but basically as absorbance increases, so does
concentration. (papers with graphs will be given in person)
2. Choose a solution from the simulation and measure the Absorbance for
different concentrations on the preset wavelength setting.
Data from the Simulation
1
Concentration
________M
Abs
0
100
200
300
400
0
0.4
0.90
1.32
1.62
(graph is also exponential bc as absorbency increases, so does concentration.)
3. How does your second graph compare to your prediction?
The prediction and results were strikingly similar.
4. Based on Beer’s Law (A = εlC, A = absorbance, ε = molar absorptivity, l =
pathlength and
C = concentration), do you expect using different
wavelengths of light would change the way your previous graph looks? Why or
why not?
No, because concentration will always increase with absorbance.
INVESTIGATING ABSORPTION
AND
WAVELENGTH
1. a. Compare three solutions of different colors with the same pathlength (width
of container).
Preset Wavelength:
Simulation default
setting
Solution
Solution Color
CoCl2 Cobalt
Chloride
KMnO4
Potassium
Permangana
te
K2CrO4
Potassium
Chromate
Beam Color
Value (nm)
Abs
Variable Wavelength:
Set to same color as
solution
Beam Color
Value (nm)
Abs
549 nm
0.39
639 nm
0.14
544 nm
0.10
411 nm
0.01
411 nm
0.27
612 nm
0.00
b. What combinations give the most absorbance? Why?
The peach colored one with 549 nm because the green is absorbing the peach.
c. How are beam color, solution color, and absorbance related?
The darker the color, the higher the absorbance.
λ(nm)
Abs
2. a. Choose a solution and keep concentration and pathlength constant as
you graph the absorbance for different wavelengths.
Solution: KMnO4
380
580
Wavelength (nm)
780
(graph will be given in person)
b. What is the value for the “preset” wavelength for your solution? Mark
this point on your graph.
The “preset” wavelength value for KMnO4 is 544 nm.
c. Why do you think the “preset” wavelength is the best wavelength to
use for this solution?
It has the most absorbency. (2.0)
3. Compare your absorbance spectrum sketch with a group that chose a different
solution. Would you use the same wavelength of light to do spectroscopy
experiments with different colored solutions? Why or why not?
No because all solutions are different.
4. In a lab experiment monitoring the change in concentration of a reddish-brown
substance, FeNCS2+, a wavelength of 455 nm is used.
a.
Does this wavelength agree with your conclusions about beam
color, solution color, and absorbance above? Why or why not?
Yes, the reddish-brown substance will absorb the blue wavelength.
b.
What other wavelengths might you consider using for FeNCS2+
spectroscopy?
A wavelength around lower 500s.