Here’s an EGGcellent Science Experiment to Introduce Osmosis

Did you know that you can observe osmosis with ingredients that might already be in your kitchen? With only an egg, vinegar, corn syrup, and food coloring, this fun science experiment can shine some light on the invisible but indispensable process of osmosis, reveal the power of the semipermeable membrane, and create colorful eggs just in time for Easter!

 

Maybe you are homeschooling, teaching science online from your home, or interested in hands-on education for your kid(s) at home. This simple experiment will demystify osmosis using the natural semipermeable membrane found just under the shell of every egg. Semipermeable membranes are in fact crucial components of all living cells. Just like individual eggs, cells take advantage of osmosis to maintain the water content and tonicity that they need in order to function.

            

What is a semipermeable membrane?

It is simply a membrane that allows only certain molecules to pass through it.

 

What is osmosis?

Using Merriam-Webster’s definition, osmosis is movement of a solvent (such as water) through a semipermeable membrane into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.1

 

But what really is osmosis? Why does this movement of the solvent happen?

It is a commonly misunderstood process, so five scientists may give you five different answers. Nevertheless, on a molecular level, the solvent’s movement happens for a physical reason. Like all physics problems, this can be explained using potential energy or using forces. Looking just at the forces, a lower solute concentration is equivalently a higher solvent concentration. With the solvent molecules thermally creating diffusive forces in both ends of the microscopic pores in the semipermeable membrane, but a higher concentration of solvent molecules on one side, a net force is created across each pore. An egg has up to around 17,000 of these pores!2 These net forces add up over the total area of all pores in a semipermeable membrane, and that total pressure is called the osmotic pressure. This osmotic pressure results in osmosis.

 

So how do I perform this experiment?

You will need:

  • 1 egg
  • 2 glasses
  • vinegar
  • corn syrup
  • food colouring
  • water
  • 1 heavy spoon / 1 more glass
  • patience (this takes 4-5 days!)

 

Steps:

 

  1. Check that there are no cracks in the egg, and then carefully place the egg into the glass.
  2. Pour vinegar into the glass until the egg is completely covered.
  3. Wait 24 hours.

 

The egg will become a “naked egg” when vinegar’s acetic acid dissolves the calcium carbonate eggshell. Simultaneously, the egg will inflate as water in the vinegar osmotically diffuses into the egg through its semipermeable membrane.

 

  1. If the egg shell is not completely dissolved yet, pour out the vinegar and pour in new vinegar over the egg. Then wait another 24 hours.
  2. Pour out the vinegar.

 

Now you have a naked egg!

 

  1. Dry the glass or use another. Pour in just enough corn syrup to cover the egg.
  2. Hold the egg down with a heavy spoon or another glass.

 

Corn syrup is only 24% water, so the water still contained in the egg will diffuse outward through its membrane. It is also denser than water, making the egg buoyant.

 

  1. Wait about 48 hours.
  2. Pour out the corn syrup.

 

Now you have a small, shrivelled egg!

 

  1. Dry off the shrivelled egg. Place it in a new glass and fill the glass with water. Put 3 drops of food coloring in the water. Pick any color you wish!
  2. Wait 24 hours.

 

Osmosis is occurring for the last time as the egg slowly fills with the colored water.

 

  1. Pour out the colored water.

 

And now, you have a colorful egg!

 

Let’s briefly summarize everything that happened. We started with a chemical reaction that dissolved the hard outer shell and released small carbon dioxide bubbles. Water filled the “naked egg” thanks to the egg’s semipermeable membrane that allows only water and air to pass through it. The corn syrup received most of that water by osmosis. Here’s a challenging question: Why did the egg collapse and shrivel up? It was not the weight of the corn syrup but rather the osmotic pressure itself which pushed the corn syrup and thus collapsed the egg at its flexible, semipermeable membrane. Meanwhile the water exited the egg as the membrane was pushed inward, until only a small core of the egg remained. After that, the egg had a very low concentration of water, and accepted all of the colored water that it could hold.

 

If the membrane had instead been inflexible and strong enough to support a decrease in pressure as the water diffused out of the egg, it could have pushed the corn syrup up against gravity while pushing the water out. Osmosis can perform work. For this reason, reverse osmosis (RO), which moves water the opposite direction against the concentration gradient, requires a pump producing several million pascals in order to overpower the natural power of osmosis. Both forward (FO) and reverse osmosis can be very useful, whether for lab work, filtering wastewater, desalinating salt water, or a multitude of other applications. New applications of FO and RO membrane technology are constantly being discovered.

 

Hopefully we successfully helped demystify osmosis! From all of us at Sterlitech, Happy Easter!

 

References

  1. https://www.merriam-webster.com/dictionary/osmosis
  2. https://www.scienceofcooking.com/eggs/anatomy-of-a-chicken-egg.html
  3. https://www.youtube.com/watch?v=SrON0nEEWmo