Beer's Law Simulation Instructions

7/29/2019 Beer's Law Simulation Instructions

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COLORED SOLUTIONS AND SPECTROPHOTOMETRY

An aqueous solution containing an ion that is colored results in a colored solution.

Usually theses ions belong to compounds of the transition metals. Much information

can be derived from this phenomenon.

However, before this information can be used, one must understand the factors that

affect the color.

Open the link on my website for Beer’s Law Simulation. The tabs at the bottom

read: Intro, Concentration, Path length, Wavelength, and Transmittance, Some

Errors, Bad Cal, Glossary, and Feedback.

All you will be doing is looking at the reference data on these pages and drawing

conclusions to help you understand UV-Visible Spectrometry.

Concentration Tab:

1. How are concentration and absorbance related?

2. Determine a line equation for the reference and for the sample relating

concentration and absorbance.

3. Explain the meaning.

4. Determine how this would be useful in determining the concentration of a

solution of this substance that was unknown.

Path length tab:

1. How are concentration and path length related?

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2. Determine a line equation for the reference and for the sample relating

concentration path length and absorbance.

3. Explain the meaning.

4. Explain why the containers for a spectrophotometer are usually matched up

to each other prior to use.

Wavelength Tab:

1. Determine the wavelength at which this solution absorbs the maximum

amount of light(λmax)

2. How is absorbance related to transmittance?

3. Determine the wavelength of minimum transmittance.

4. Using outside resource, determine the predominant color of the solution and

explain how this impacts the choice of wavelength used in a

spectrophotometer for this particular solution.

5. What would happen if a wavelength of 440 were used? How about 475?

6. Would the wavelength used in this experiment work on a purple solution or a

red solution? Why or why not.

Transmittance Tab:

1. How does transmittance relate to concentration?

2. Determine or look up a curve equation that relates transmittance to

concentration.

3. Using outside resources, determine why the graph for transmittance is not

the same as that for absorbance.

4. Determine or look up the equation that relates absorbance to transmittance.

Ponder these questions:

1. Write an equation that relates both concentration (c) , and pathlength (b) to

absorbance (A).

2. How would leaving the lid of the Samplecompartment open influence the

results?

3. How about the addition of fingerprintsbeing adding to the Spec tube?



4. How about suspended material in the sample?

5. If the suspended materials slowly settledwhat would happen to the

absorbance?

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Beer's Law Simulation Instructions