Serial Dilution and Beer’s Law

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VIDEO LINKS:

Lab Experiments (Write protocols and perform experiments based on these):

  1. Making Kool-Aid Stock Solution
  2. Serial Dilution with Kool-Aid
  3. Recording the Visible Spectrum
  4. Beer’s Law with Kool-Aid Solutions

Prelab (must be submitted before the experiment) includes: Experimental Protocol, Chemical Table and Equipment Table.

The lab report requires all sections (including prelab sections) to be completed in one document.

Experimental Protocol

(Analysis) Watch the experiment videos and take notes on the protocol.  Stop the video and re-watch as necessary to acquire the details of the procedure.  Write out the protocol for each part of the experiment in sequential steps.  Bullet points and numbering of steps works better than paragraphs.  This is the protocol you will follow, so be detailed!

Chemical Table

(Representation) Prepare your chemical table including the materials you will use in the experiment.  Here is a general template that you may use.
Chemical Name Chemical Formula Molar Mass (g/mol) Hazards reference PPE
Sodium Chloride NaCl 58.5 Skin irritation https://fscimage.fishersci.com/msds/21105.htm

Equipment Table

(Analysis) Identify the equipment (type AND size) needed for the experiment and include the name and an image of each.  Be sure to describe the equipment, how to use it, and why it is suitable for this use.
Equipment Name Equipment Picture Intended Purpose

Data Collection

(Acquiring competencies) Following your detailed protocol based on the videos, perform all the experiments. Record your observations and take pictures of your key steps in the process.  Your observations and images need to be incorporated in your data section and this section should be as detailed as possible as you will use this information to complete your discussion.

Data Processing

  1. (Representation) State Beer’s Law and identify each variable.
  2. (Existing knowledge, research, and views) Find a literature value for the molar absorptivity (ε) for red food-dye 40 with its associated wavelength and provide a reference for your source. Provide a reference.
  3. (Manipulation) Assuming that your identified literature value for molar absorptivity (ε) is correct, use the absorbance value of your stock solution to calculate the red food-dye 40 concentration of your stock solution.
  4. (Manipulation) Using the calculated molarity of the stock solution, calculate the molarity of each diluted sample of red food-dye 40.
  5. (Representation) Graph your data for each peak in the serial dilution where the x-axis is the concentration, and the y-axis is the absorption.
  6. (Manipulation) Calculate a value for molar absorptivity (ε), based on graphing your data for each wavelength you selected for the Beer’s Law experiment.
  7. (Manipulation) Calculate the error of your experiment by calculating the percent error for your molar absorptivity (ε) values to the literature values at the designated wavelengths.
  8. (Manipulation) Assuming that the initial concentration of your red food-dye 40 source is 100 ppm, calculate the molarity of your prepared stock solution.
  9. (Manipulation) Assuming that your identified literature value for molar absorptivity (ε) is correct, use the absorbance value of your stock solution to calculate the red food-dye 40 concentration of your original source.
  10. (Manipulation) Calculate the percentage below the 100 ppm limit the Kool Aid original source is found to be.
  11. (Assumptions and Analysis) Fill in the following table using the observations and data from your experiments.
Assumptions made Testing the assumption If assumptions are wrong ...
The distilled water is pure Evaporate it and check for residue The density would change depending on the density of the contaminant

Discussion

Write a minimum one-page (12 font, single spaced) discussion on the experiment conducted this week. Address at least one question in each category as fully as possible integrating the collected data, providing explanations for the observed trends, and evaluating whether your original assumptions about the experiment were validated by the results. The assignment will be graded on completeness, clarity of the explanations and the meaningful integration of the collected and calculated data. Correct grammar and appropriate format for the chemical formulae and chemical reactions is expected. You may use the outline included at the end of this document on how to build your essay to address each category.  
  1. (Existing knowledge, research, and views) Define serial dilution and relate it to the experiment you performed. Provide a reference.
  2. (Representation) Write the expression for calculating the concentration of solutions prepared through serial dilutions. Define each variable.
  3. (Experimental design) Explain the process you used to select the wavelengths that you used for your Beer’s Law experiments.
  4. (Analysis) Give a supported argument for measuring absorbance rather than transmittance in a Beer’s Law experiment.
  5. (Analysis) Describe the relationship between the absorbed wavelength and the observed color of your solution. Use the maximum absorbance wavelength for the red food-dye 40 solution as example.
  6. (Analysis) Predict the approximate wavelength associated with maximum absorbance for a yellow food dye.
  7. (Analysis) Provide a supported argument for what makes Kool-Aid or Gatorade with red food-dye 40 a good choice for this experiment.
  8. (Assumptions and limitations) Provide at least 2 reasons why carrots, beets or red cabbage may work differently for this experiment.
  9. (Assumptions and limitations) Identify at least 2 properties that a solution must have to be suitable for a Beer’s Law experiment and provide a supported argument for your choices.
  10. (Analysis) Comment on the precision of your collected data using the R2 values from your Beer’s Law graphs.
  11. (Analysis) Comment on the accuracy of your collected data using the percent error values from your molar absorptivity (ε) calculations.
  12. (Analysis) Comment on the accuracy of the 100 ppm concentration of your source solution. Could the company have exceeded that concentration?

Recommended Discussion Outline:

First paragraph (Existing knowledge, research, and views):

  • Define solubility
  • Define Beer’s Law
  • Define visible light
  • Define the role of the spectrometer and how it works
  • Define absorption
  • Define how concentration and absorbance are related using a graphical representation

Middle paragraphs (manipulations and analysis):

  • Analysis questions with reference to graphs and calculations
  • Experiment design elements
  • Discuss assumptions made

Next to last paragraph (experimental design):

  • Suggest future experiments that could add value to this experiment

Last paragraph:

  • State what you learned by executing this experiment (techniques, theories, analysis, …)
  • State specifically how this experiment relates to the theory that you learned in lecture
  • State how this relates to your life