Denaturing
Experimenting with milk
Although we are not sure what Carver taught his students that first year, we can guess that because he had spent a great deal of time studying the dairy industry and products in Iowa, that this could have been a part of the curriculum. Tuskeegee had been a farm and there were milk cows, so he may have started with some simple analyses. Additional background information can be found at the bottom of this page.
In the following explorations, students will use their new equipment to study the characteristics of milk. It is best to use skim milk or powdered milk in these experiments. If 1% 2% or whole milk is used, the white solids contain fat. This may be an interesting variable to introduce, if desired.
Note: At this point, consider again how Carver built his laboratory and generalize to the effort scientists make to care for their laboratory space and to find the tools they need. It is also worth explaining that there are strict laws about what one may and may not discard in the trash or down a drain. Scientists have strict protocols for how they discard chemical materials. Since most of what we use in this unit is food-related, used chemical materials can be disposed of as food is disposed.
Brainstorm with the class how they will:
• Ensure a supply of water for their experiments?
• Store and label chemicals such as vinegar, sugar, borax etc?
• Keep their work station clean?
• Remove liquid wastes without pouring discarded materials in the sink or trash?
Denaturing Milk
Materials Needed
• Stove, pan and graduate cylinder
• Small container for holding liquid
• 50 ml of milk per group
• 5 ml vinegar
• Lighter or matches for the teacher
1) Pour about 50 ml of milk into your clean pan. (Use your new graduated cylinder for this purpose.)
2) Heat the milk gently over your candle heating stove until it is just warm. (100 degrees F if you have a thermometer. If not, test the milk temperature as one would test milk from a baby’s bottle--on the wrist)
3) When the milk is warm, add 5 ml of vinegar. Stir. Note the reaction of the curds forming from the whey.
4) Carefully separate the liquid whey from the clabbered (white curdled) milk by straining it through a filter. Cheesecloth or a paper filter made from paper towels can be used. Fold the paper towel to make a filter as shown below:
Making Glue
Now the milk is in two parts: the watery whey and the solid proteins (and fat if you have used anything but non fat milk). In this next segment, students will add a polymerizing agent to the proteins to form a chain of proteins.
Materials Needed
• Clabbered milk
• Mixing cups
• Spoon or stirring rod
• Borax
• 1/4 teaspoon measure
• STEM Notebook for students to record all their work
1) Separate the clabbered milk into two cups. This way two different polymerizing experiments can be attempted.
2) To one cup add 1/4 teaspoon of powdered borax. To the other suggest to students that they choose either a larger amount of borax or that they add a measured amount of whey back into the mixture. Stir the mixtures with separate spoons. Make sure each cup is clearly labeled. Be sure to record the work in the STEM Notebook with drawings, labels and written text.
3) Watch the mixture carefully as you stir. Describe the activity of the mixture in the Notebook.
4) When the consistency reaches the researcher's satisfaction, try out the product (glue) by pasting samples of materials together. Samples could be different types of paper or fabrics or plastics or other items. This glue will require drying time, so it may be convenient to set aside the samples over a period of time to determine the results. Again, be sure to draw, label and describe in the STEM Notebook.
5) If the consistency of the mixture is very dry and clay-like, the students can mold the mixture into a desired shape rather than try it as a glue. Instead of glue, this kind of polymer becomes a basic plastic--the kind used to manufacture buttons for much of the 19th century.
Chemical Engineering
How effective is the glue? How could we tell? How can the different glue formulas be tested? Certain chemical engineers are interested in this kind of research because they can bring products to the market and advertise that they have "Gorilla Glue" see http://www.gorillatough.com/
Engineers connect the knowledge of science, scientific processes, and technology to the specific problem they are addressing. Carver used his knowledge of basic agricultural science (chemistry, the scientific method, and the use of laboratory equipment) to extend his research into finding new uses for agricultural products. For example, he used his knowledge of the chemistry of milk proteins to study the proteins of peanuts. In this unit, student engineers extend their knowledge of the basic chemistry of atoms and compounds to learn about proteins and polymers. Students also extend their understanding of scientific process and use of laboratory equipment to new purposes.
In this section, students think like engineers to test glue strength. There are two basic parts: 1) making sure they have an accurate formula for what they are advertising, and 2) using a systematic way to test the power of their mixture.
Students should carefully plan their protocols (methods and rules) for how they will do the tests. It is also important to help students at this point to keep good records of what they have done in the STEM Notebook. The exact formulae they use and the results they get are in a series of trials make up part of the process scientists use to “find out” about the natural world.
1) Repeat the processes above to separate the protein from milk. Set aside portions of the protein (casein) for additional trials of specific amounts of borax, say 1/8, 1/4, 3/8 teaspoon (or gram weight if there are available scales). Or, consider another variable, skim milk, soy milk, 1% milk etc. Have students set the formulas for at least three different trials.
2) Have students design a testing apparatus. Cut test materials (paper, etc.) so that the surface area of contact is the same throughout the trials. Text the glue by pulling the test materials apart. Have students experiment with different ways of pulling the test papers apart. How will one know the force necessary to pull the paper apart? How will the test remain consistent so that the strength of the glue can be verified?
Guiding students with possibility thinking is important. Suggest tools such as meter sticks and area computations, spring scales and methods to ensure that the paper will not rip before the joint fails.
This photo shows one way of testing the strength of glue
3) Give students an opportunity to provide both analysis and promotion of their formula and ideas through poster sessions, oral presentations or written reports.
Assessment
Students in this first segment of the unit are asked to create their own lab equipment and to conduct an inquiry in chemical engineering. Science concepts and vocabulary as well as engineering process skills can be assessed. A rubric that would assess students' ability to keep accurate journal notes and data is another possibility. See sample rubrics here.
Content can be assessed by testing students' knowledge of core concepts and content. A sample assessment tool can be found here.
Extension
See Making a Recommendation to help students understand how the role of the engineer is to use science and technology to address human needs.
Content Information
Carver knew that milk was composed of water, fat, protein, sugar and other trace ingredients. Milk is a colloid. A colloid is liquid where solid materials are help up into the water for an extended amount of time by loose chemical bonds. A colloid can also be a mixture of other kinds of materials. Fog and smoke are colloids. Fog is water suspended in air. Smoke is particles suspended in air. Milk is an example of a colloid because fat and protein are suspended in a liquid. Colloids remain able to suspend their particles for a long time and will remain unchanged unless there are external influences.
A good representation of the difference between solutions, colloids and suspensions can be found at
Representation used by the authors to demonstrate how larger molecules of a colloid are held up by water molecules. In milk, the large molecules of proteins are held in place but are not in solution.
When an acid is present, for example, the bonds are weakened and the protein can no longer remain upheld by the water and are precipitated, or pulled-out of the colloid. The acid further takes the protein apart into small particles. This is called denaturing (or altering) the protein.
Milk can be separated into the two basic components, whey and curds, by adding acid. Stomach acid from a cow, called rennet, it used for many food processes. Other acids like vinegar also work.
Milk is often first separated from its fat or cream component by spinning, agitation or centrifuging. Skim milk or nonfat milk is left after the fats are removed.
Vocabulary
Suspension
Colloid
Solution
Protein
Casein
Filtration
Polymer/Polymerization
Next Generation Science Standards
PS1.A: Structure and Properties of Matter
Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it. (MS-PS1-2)
PS1.B: Chemical Reactions
Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. (MS-PS1-2),(MS-PS1-5)
ETS1.B: Developing Possible Solutions
A solution needs to be tested, and then modified on the basis of the test results, in order to improve it. (secondary to MS-PS1-6)
ETS1.C: Optimizing the Design Solution
Although one design may not perform the best across all tests, identifying the characteristics of the design that performed the best in each test can provide useful information for the redesign process - that is, some of the characteristics may be incorporated into the new design. (secondary to MS-PS1-6)
The iterative process of testing the most promising solutions and modifying what is proposed on the basis of the test results leads to greater refinement and ultimately to an optimal solution. (secondary to MS-PS1-6)
GOTO CARVER Main Page