A demonstration of denaturing protein
Introduce high school biology and chemistry students to the concept of denatured proteins with this inexpensive, fun demonstration. Your students will be amazed when you “cook” an egg in hydrochloric acid, and they will learn that a protein (egg white) can be denatured by heat, or, as shown in the demonstration, by an acid.
Important safety note: Eggs “cooked” during this demonstration are not fit for consumption.
Materials needed
Spoon
Water
6 to 12 raw, extra large eggs
Preparations
One day before the demonstration:
1. Put on safety goggles and gloves.
2. Pour 500 mL hydrochloric acid, 1 M, into the 1,000 mL beaker.
3. Use the spoon to gently place an egg in the solution.
4. Use the lab scoop to completely submerge the egg in the solution.
5. Leave the egg in the solution for 2 hours.
6. Use the spoon to remove the egg from the solution.
7. Place the egg in the 600-mL beaker and add enough water to the beaker to cover the egg. Bring it to class as an example of a fully “cooked” egg.
Demonstration
1. Put on safety goggles and gloves.
2. Pour 500 mL hydrochloric acid, 1 M, into the 1,000 mL beaker.
3. Use the spoon to gently place the egg in the solution.
4. Use the lab scoop to completely submerge the egg in the solution. (Note: Buoyant white foam forms immediately. After several minutes in the solution, the raw egg slowly begins to lose its shell. It takes approximately 60 to 90 min for the shell to completely dissolve and reveal the transparent egg sac containing the soft yellow egg. The soft yellow egg “cooks” and becomes white and rubbery if it is left in the solution.)
5. Show the previously “cooked” egg.
Disposal
Pour the used hydrochloric acid through the funnel into your waste bottle. Dispose of the egg in the trash.
What is happening?
The acid reacts with the calcium carbonate in the eggshell to form carbon dioxide. The carbon dioxide bubbles create the buoyant white foam that you see. As the shell dissolves, the acid penetrates the permeable egg sac and denatures the protein inside, turning it white. The egg appears to be hard-boiled. Heat and acid can denature proteins. The egg sac is permeable to gases and liquids. The egg loses liquid through the sac after it is removed from the acid, so it always feels wet.
Egg facts
An average eggshell is 0.098′ (2.5 mm) thick. It is made of 3.5% protein, 1.5% water, and 95% calcium carbonate. The shell contains from 7,000 to 17,000 pores that allow gas exchange and protect the egg against microorganisms. Because an eggshell is mostly calcium, hens with diets deficient in calcium produce eggs with weak shells.
The pesticide DDT (Dichlorodiphenyltrichloroethane) also causes hens to produce eggs with weak shells. It does this by inhibiting the deposition of calcium in the shell as the egg forms inside the hen. The fragile eggs crack or break in the nest, killing the embryos inside. Although the DDT levels used in the United States were not directly toxic to birds, DDT persisted in the environment and bioaccumulated in species like the American bald eagle and osprey, bringing them to the brink of extinction. The federal government banned the use of DDT in 1972.
Additional Reading: Egg Vacuum Activity
Eggs-tension activities
Measure the pH of the solution over time using probeware.
Perform diffusion experiments using the “cooked” egg.
