Lab Report

Review the information found in this book for instructions on how to perform the surfactant experiments and write the corresponding lab report. There is also a “common mistakes” list to use as reference while you are writing.


1. Lab Report Instructions

Demonstrating the Importance of Surfactant: Lab Report

This experiment is designed to use common household products to demonstrate the function and importance of surfactant. You will be using milk and food coloring for this assignment.  Think of the milk as the water and food coloring as the gas in the respiratory system. Refer to lecture and lab information and click here to read more information concerning the importance of surfactant so that you can relate it to the concepts of this lab experiment.

Part 1: Surface Tension

Surfactants lower the surface tension of water.  To better understand this concept, you will complete the following activity to demonstrate and observe surface tension before you experiment with the effects of surfactant.  All you will need for this activity is a penny, water, and an eyedropper or pipette.

  1. Wash and rinse a penny in tap water, and then dry it completely with a paper towel.
  2. Place the penny on a flat surface.
  3. Use the eyedropper or pipette to drop individual drops of water onto the surface of the penny.
  4. Count and record the number of drops of water that will fit on the surface of the penny before the water runs off.  You will need to report this number in your lab report.

The surface tension created by the water molecules being attracted to each other is the property that surfactants work to counteract.  In the next activity, you will see the effects of a surfactant in the lungs.

Part 2: Surfactant

To observe how a surfactant works, complete the following experiment:

  1. Obtain a shallow dish and pour some milk (must be whole milk) into it so that it completely covers the bottom of the dish.
  2. Add a couple of drops of food coloring to the milk in the center of the dish and observe for two minutes.  At the end of the two minute time period, measure from the center of the food coloring to one edge of the food coloring.  This will give you the distance the food coloring moved outward during the two minute time period.  Record this number in millimeters to include in the results section of your lab report. You also need to calculate the rate of movement in millimeters per minute for the results section of your lab report.
  3. Add a couple of drops of dishwashing liquid to the center of the dish. Observe what happens to the food coloring and milk.  Observe for two minutes, and once again measure from the center of the food coloring to one edge of the food coloring.  Record this number in millimeters to include in the results section of your lab report. You also need to calculate the rate of movement in millimeters per minute for the results section of your lab report.
  4. As a control you can have a dish of milk to which you only add food coloring but not the dishwashing liquid. Otherwise you may just use the sample you prepared in step 2 to make your controlled observations before adding the dishwashing liquid.
  5. Use your observations to complete your lab report.  Follow the instructions and format explained below.

Lab Report Instructions

Now that you have completed the experiment, move on to the report.  Below is an outline for the sections of the lab report to clarify what it should contain and issues you will want to address for the report.  Each section – except the cover page – should be at least 1 well-formed paragraph and should have a section heading.

  1. Abstract – Will not be done. You will follow the conclusion instructions instead.
  2. Introduction – You will want to include information about why this experiment was done. This section should also include background information on the principle components of the experiment. For example, what is the function of surfactant in the respiratory system? The introduction must also contain a hypothesis about what you expect your results to be for this experiment and why.
  3. Materials and Methods – Briefly state the materials you used and how you did the experiment.
  4. Results – Briefly present your data (results). This is not the place to offer an explanation for your results. This will be addressed in the discussion.  Be sure to include the results for both the surface tension and surfactant experiments.  Include your qualitative observations of what happened in each experiment as well as the number of water drops that fit on the penny and the distance the food coloring moved with and without soap added.  You must calculate the rate of movement (in millimeters per minute) of the food coloring before and after addition of the dishwashing liquid.  You must also calculate the percent change in rate of movement after addition of the soap.  Your results can be presented in your choice of or a combination of text, data tables, and images.
  5. Discussion –In this section you will want to 1. explain/discuss your observations and results. For example, state whether more or fewer drops than you expected fit on the penny, and explain the reason for this.  Also, for the second experiment, explain the differences that you saw before you added the dishwashing liquid and after you added it. This includes comparing the speed of movement of the food coloring before and after the addition of the dishwashing liquid. Why was the speed affected? 2. You will also want to address how this experiment relates to the ultimate question: What is the importance of surfactant? How does the addition of the dishwashing liquid affect the interaction of the food coloring and the milk? Do the dishwashing liquid and surfactant perform similar functions? 3. Address whether your data supports the hypothesis that you presented in the introduction. 4. Lastly, this experiment allowed you to observe what happens between the food coloring and milk in the absence of the dishwashing liquid. Compare this to the respiratory system – what would happen to the interaction of water and gasses if surfactant was not present?
  6. Conclusion – Keep this to a single paragraph that restates the basis for the experiment and what you found. This is basically a summary of your entire report. Look at the instructions for the conclusion as a guide.  As a part of your conclusion, you need to explain how changing the experiment might impact the results.
  7. Literature Cited – You all know my policy on plagiarism. Don’t do it or there will be consequences. This applies not only to plagiarism of another student’s work but also of a reference material. You must appropriately cite, in APA format, all material used. Be sure to use your own words in your report. This will ensure that you understand the material to the best degree possible.  Click here to see examples of how to create proper in-text and reference list citations in APA format.  The “Common Mistakes on the Surfactant Lab Report” link under the Lab Report Instructions heading in Unit C of this class will be of help in finding scholarly sources for your report.  Sources should always be listed alphabetically by author’s last name. Acceptable scholarly sources include: hardcopy books, eBooks (including your eText), scientific articles, scientific magazines (National Geographic, Scientific American, Popular Science, Discover Magazine, etc.).
    1. Use the library’s online database to help you search for proper material. The Academic Search Complete is a large database full of research articles. There is also an eBook database for electronic textbooks
    2. Unacceptable sources – Wikipedia,, other non-science websites, really websites in general. I will deduct points for not using proper sources.
    3. You must use in-text citations. It is not enough to list your literature cited at the end of the paper, you must also make notations in the body of your paper to show where each of your facts came from. Failure to properly cite within the body is a form of plagiarism.

Format: APA format (see link above for proper formatting of cover page, section headings, and citations), double spaced, 12 pt. font, 1” margins, Times New Roman, no direct quotations (practice paraphrasing). No set page length – as long as it takes to cover all details for each report section. At least 3 scholarly citations. 


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