I’m sure “kids of all ages” will enjoy it as a Woodloch-at-Home activity!
As a medical scientist I see that this project can also be a fun learning opportunity. It shows the physical chemistry concepts of hydrophobic, hydrophilic, and lipophilic. (“Density” does explain why the water sinks below the oil, but not why water stays together in globules when it “erupts” up into the oil.) These principles have applications not only in lava lamps but also biology, corona-virology, and even hand-washing with soap!
First, the concepts. Start with the proverb that “oil and water don’t mix.” This saying refers especially people who don’t get along with each other – and doesn’t apply to Woodloch guests, since we all try to live up to the “spirit of the Woodloch games.” The proverb is based on the observation that literally oil and water cannot blend together, no matter how hard you shake them or stir them up with Alka-Seltzer.
Physical chemists (who study the properties of how different materials behave in the visible world) now know the chemical explanation for this. Water is H2O, 2 hydrogens and 1 oxygen arranged in a V, which gives each molecule an electrical property, positive at one side and negative at the other. This allows it to dissolve salts like sodium chloride (table salt) or like the citrate and bicarbonate salts in Alka-Seltzer. Oil, on the other hand, is made of fatty acids, which chemically are long chains containing carbon and hydrogen. Those chains are strongly bonded, which means that they are not electrical and will not dissolve in water.
So, the electrical water molecules are all attracted to each other, and the non-electrical fatty acids molecules in oils are crowded out from water. Physical chemists refer to this property of oils being repelled by water as “hydrophobic,” from Greek hydro = water and phobia = fearing.
Physical chemists and biologists divide all substances in our bodies according to how they react to oil or to water. Some body chemicals like proteins or enzymes are hydrophobic, and will not dissolve in the water; instead, these proteins and enzymes are lipophilic, from the Greek lipid = fat and philio = love. Other proteins and enzymes are hydrophilic, meaning they “love” to dissolve in water.
This chemistry allows us to understand lava lamps, cells, the coronavirus, and handwashing. The water in the lava lamp stays together in globules inside the oil because the two won’t mix.
Cells have an outer membrane, like a tiny microscopic balloon, made of fatty lipid. Inside the membrane is the cytoplasm which is a watery solution of proteins and enzymes. The water inside the cell won’t leak out because the lipid membrane keeps it all inside.
Many viruses, including the now-famous coronavirus, have a primitive envelope of lipid covering them similar to a cell membrane.
What does this have to do with hand-washing? Soap is key. Soap chemically blends fat and a salt (sodium hydroxide). So the fatty part of soap is lipophilic, and will attract lipids, while the other part of soap is hydrophilic, meaning it will dissolve in water.
So, when you wash your hands with soap, the lipid membrane of the coronavirus combines with the fatty part of the soap, and then the hydrophilic part of the soap carries it away into the drain water.
Thank goodness that scientists figured out that the virus has a fatty covering, which something simple like soap can wash away! Meanwhile, it’s fun to see with our own eyes how chemistry works in a lava lamp!
Breaking this down by age group, here are some simple teaching messages.
Pre-school age: See how different things – like oil and water and coloring – act with each other. Try changing a few things – the dye color or how much Alka-Seltzer you use. This is called “experimenting.” (You already did that very well!)
Elementary school age: Oil and water don’t mix because they’re made of different chemicals. Here’s a fun fact. Have you ever tried to wash something sticky like oil or egg off your hands or off a dinner plate using just plain water? It doesn’t work, because water will not dissolve oily things. That’s where soap comes in. Soap is a chemical blend of fat (called glycerides) and salt (alkali). The fatty end of the soap chemical will soak up oil or egg, and the salt end of the soap chemical will dissolve in water. The soap lets you wash the oil down the drain in the water. Question: What do you think would happen if you poured a couple of tablespoons of dish soap into the lava lamp? (Answer can be found at: http://coolscienceexperimentshq.com/mixing-oil-water/ )
Middle school age: Did you know that your body cells and viruses are made of oil and water? The outer coat of each body cell is like a tiny balloon of oil called the “lipid membrane.” It’s so small you can only see it through a microscope. Inside the lipid “balloon” is the watery part of the cell called “cytoplasm”. The watery part can’t leak out of the membrane because oil and water don’t mix – the membrane holds the water inside the cell. Viruses – like the coronavirus – also have an outside coat called the “lipid envelope.” What do you think happens to a virus particle on your hand if you wash with soap? (Answer: the soap breaks up the outside oily lipid envelope, and washes the virus down the drain.)
High school age: This would be an introduction to organic chemistry, and take away the fun of the lava lamp. We’ll leave that to the high school science teachers!