This is a chemistry experiment, even though you are doing it in your mouth! It illustrates a very important concept in chemistry called solubility, which is the ability of one substance to dissolve another substance.  Chemists say that “like dissolves like” and this is an example of that.  If your gum was candy coated, like a Chiclet or gum-ball, you should have noticed that the candy coating dissolved or disappeared as soon as you began chewing.  This is because the candy coating was made of sugar, which easily dissolves in water (try adding a spoon full of table sugar to a glass of water and watch what happens), and the saliva in your mouth is mostly water.  Chemists would say that sugar is soluble in water.  Saliva and chewing are the first steps in digesting or breaking down your food into simpler components that your body can use for energy.

Your saliva does not dissolve the gum, however, because most modern chewing gums are made of a synthetic rubber (i.e. man-made, not natural), which is a type of oil-based polymer, such as  butadiene-styrene, vinyl acetate, or polyethylene (the same material in plastic grocery bags).  You may have already learned that oil (as well as oil-based substances) and water don't mix- they are not alike.  But chocolate does contain oil-based fatty substances, so the chocolate dissolves the gum.  Like dissolves like.  After adding the first piece of chocolate and chewing you should have noticed that the gum was much softer and stickier, and maybe much smaller than it was after you first chewed the gum alone.  If you add enough chocolate to the gum in your mouth (you may need 3 or 4 pieces) and continue chewing you should be able to make the gum disappear completely! 

If you're not allergic to peanuts, try chewing a spoon full of peanut butter with your gum instead of chocolate.  Does the peanut butter also make the gum disappear?  Why do you think that is?

Instead of doing the entire experiment in your mouth, just chew the gum for a minute or two in your mouth, then put it in a cup or small bowl instead.  Add a couple spoonfuls of vegetable oil to the cup and use a spoon to stir and grind the gum.  Does it dissolve?  If not, add a little more vegetable oil.  Try repeating ths experiment with some other liquids.  Is gum more or less soluble in other liquids?

Solubility has it's limits, however, and you can easily test this.   Add one or two spoonfuls of sugar to a glass of water and observe what happens.  Does all of the sugar dissolve immediately?  Observe for a minute or two, has more dissolved?  Use a spoon tp stir the water and sugar.  Does it dissolve more easily?  Try adding more spoonfuls of sugar and stirring.  Does the sugar continue to dissolve?  Keep adding sugar until it will no longer dissolve in the water.  Now you have reached the solubility limit- the water simply can't hold any more sugar and we say it is saturated.  What would happen if you added more water to the glass?  Solubility also depends temperature.  With the help of an adult try repeating this experiment with warm or hot water.  Is sugar more soluble in hot water, i.e. can you make more spoonfuls of sugar dissolve?

Coming soon:

make rock candy
float letters off M&M's
pop rocks
dancing raisins
carbonated soft drinks
Lava Lamps
Dissolve egg shell in vinegar
Underwater fireworks (food coloring dissolves in water but not oil)
Oil-based and water-based paints
​

Journal of Chemistry Education Classroom Activity #105. A Sticky Situation: Chewing Gum and Solubility 

• https://pubs.acs.org/doi/pdf/10.1021/ed800135j

​
Learn more about solubility:

• https://en.wikipedia.org/wiki/Solubility

Coming soon:

Saliva
​Digestion
​Solubility experiments

Iron is a crucial component of a balanced diet (there should actually be enough iron in your body to make one or two small nails), but some people might not consume enough iron naturally to sustain themselves.  Because of this, many food manufacturers add iron to some foods to boost the average daily intake of this important mineral.  Some  foods may use a chemical form like ferric orthophosphate (FePO4) or ferrous sulfate (FeSO4), but most cereals simply use elemental (i.e. the pure atom) iron (Fe), also called "Reduced Iron".  

The iron you see in your cereal is elemental iron- actual metallic iron filings or shavings similar to the little flakes you might see come off of a steel wool pad when you squeeze or rub it, just much smaller.  That's right, you're eating metal in the morning!  But not to worry, acids in your digestive tract can change this metallic iron into a form that is easily absorbed and used by your body.  [Note: if you don't see any iron particles in this experiment you probably have a cereal that add one of the chemical forms listed above, so try a different cereal instead.]

These very tiny metal particles are mixed into the rest of the cereal ingredients, which is why you don't normally see them, but a magnet will attract these small iron filings that are present in the cereal, separating them from the other cereal components which are not attracted to the magnet (there's more information about magnetism in the reference links below).  Crushing the cereal and mixing it with water makes it much easier to separate the iron.  By the way, this is also why you need to use a wooden popsicle stick or plastic spoon to stir in Step 8 of the procedure above (if your cup doesn't have a lid).  Most metal spoons are made of steel, which contains a lot of iron and therefore will also be attracted to your magnet (although some types of steel are actually not very magnetic at all).

​Separating iron from cereal requires a powerful magnetic field, which is why we need to use a strong neodymium magnet, which is actually made from the elements neodymium, iron and boron (Nd2Fe14B).  Neodymium is rarely found in nature, so these magnets are sometimes called Rare Earth magnets.  Neodymium magnets are usually plated with a thin layer of another metal like nickel so they look like they're metal, but they are actually a type of ceramic.  Ceramic materials are similar to glass, so these magnets are fragile and can shatter or break quite easily, often producing sharp edges, if you allow them to slam together.  Because of this as well as their strength they must be handled very carefully.

Some breakfast cereals contain much more iron that other cereals.  You can find out how much iron any cereal contains by reading the "Nutrition Facts" labels on the side of the box (like the photo above).  For example, "Total" cereal contains 100% of the recommended daily iron allowance, while "Shredded Wheat" contains only 8% - this is why you should see more iron filings from the Total cereal.  Test several different cereals, does the amount of iron you see agree with the information on the labels?  Is it important that you use the same amount of each cereal and shake it for the same length of time?  Is it important to use the same amount of water?  Why or why not?
​

After you have separated the iron from the cereal and water mix and rinsed the cup with water, carefully remove the magnet from the bottom of the cup.  Be sure not to tip the cup as once the magnet is removed the iron particles will be free to move.  Add a little bit of water to the cup and gently stir or swirl the cup to mix the iron particles.  Now hold the magnet near the sides or bottom of the cup and observe how the tiny iron particles move.  Try holding the magnet in different positions.  How does this affect the movement and orientation of the iron particles?  If you're careful you may be able to observe the shape of the magnetic field lines that surround the magnet.  You can also try this with a little bit of vegetable or baby oil instead of water in the cup [first tape the magnet to the bottom of the cup again to attract and pin all the iron, then carefully dump out the water and gently dry the cup without disturbing the iron particles, then add the oil].  How does the oil affect the motion of the iron particles?

If you hold your magnet near a flake of piece of the cereal, does it move?  What if you crush the cereal into smaller pieces?  Try floating a piece of cereal in a bowl of water, then holding the magnet very close.  Does it move now?

Another way to do this experiment is to place your magnet inside a small balloon, squeeze out any air inside, then tie it.  Now simply drop the balloon into your bowl of mashed cereal and water mixture, attach the lid and shake several minutes as before.  Open the lid, remove the balloon and rinse it with water to see the iron filings stuck to the balloon.

If you want to try another cool science experiment with your left over cereal (although it has nothing to do with iron or metal), check out the "Cheerios Effect" (see reference link below).  As the name suggests, it works best with Cheerios, but try it with other cereals too.
​

Other variations of this experiment:

• https://mocomi.com/iron-in-cereal/
• https://www.scientificamerican.com/article/get-the-iron-out-of-your-breakfast-cereal-bring-science-home/
• https://www.stevespanglerscience.com/lab/experiments/eating-nails-for-breakfast/
• https://www.sciencebuddies.org/science-fair-projects/project-ideas/BioChem_p027/biotechnology-techniques/iron-in-breakfast-cereal
• https://www.education.com/science-fair/article/iron-in-breakfast-cereal/​

Why iron is so important for your body:

• https://www.cdc.gov/nutrition/InfantandToddlerNutrition/vitamins-minerals/iron.html
• https://www.eatright.org/food/vitamins-and-supplements/types-of-vitamins-and-nutrients/iron
• https://www.herzindagi.com/diet-nutrition/top-foods-high-iron-why-iron-is-important-for-body-article-158578

​
​Which breakfast cereals have the most iron:

• https://foodwithiron.com/breakfast-cereals-high-in/
• https://tools.myfooddata.com/nutrient-ranking-tool.php?nutrient=Iron&foodgroup=Breakfast-Cereals&sortby=Highest

Iron and magnetism (ferromagnetism):

• https://sciencing.com/why-does-magnet-attract-iron-4572511.html
• https://en.wikipedia.org/wiki/Ferromagnetism
• https://www.thoughtco.com/not-all-iron-is-magnetic-3976017

Magnetic field lines:

• https://www.thoughtco.com/magnetic-field-lines-4172630
  

The Cheerios Effect (and how it affects bugs that walk on water):

• https://ed.ted.com/best_of_web/8HDeZKFr#watch

​Los metales como el hierro y el acero se utilizan para fabricar automóviles, barcos y clavos. Es posible que también haya escuchado que necesita alimentos ricos en hierro en su dieta para una buena salud; la deficiencia de hierro puede provocar enfermedades como la anemia. Pero tal vez nunca se dio cuenta de que en realidad es el mismo hierro en cada caso. Así es, estás comiendo exactamente lo mismo que se encuentra en las uñas todos los días, ¡y en este experimento lo verás por ti mismo!

1. Place about 1 teaspoon of baking powder in one of your small cups.  
2. Place about 1 teaspoon of baking soda in another small cup.
3. Place about 1 teaspoon of water into each of the cups from Steps 1 and 2 and stir each with a clean spoon or popsicle stick.
4. Observe closely what is happening in each of the cups.  Do you see any bubbles?  Do you hear anything?
5. Add about 1 teaspoon of vinegar or lemon juice to the baking soda cup.  Do you observe anything happening now?
6. Place about 1 teaspoon of flour in a third clean cup.  Add about 1 teaspoon of baking powder and mix thoroughly with a clean spoon or popsicle stick.
7. Add about 2 teaspoons of water to the flour and baking powder in the third cup and stir.  
8. Observe closely what is happening.

Baking soda is the common name for sodium bicarbonate, a type of substance or chemical called a base.  When it is mixed with water is simply dissolves with no reaction.  Baking powder, however, contains not only sodium bicarbonate but also another type of chemical called an acid (or sometimes two different acids).  When these chemicals dissolve in water the base sodium bicarbonate reacts with the acid.  This is called a chemical reaction because it results in the creation of one of more new and completely different substances.  Acids and bases often react with each other.  In this reaction the new substance is a gas called carbon dioxide, which is the tiny bubbles that you observe.  You can also hear them popping as the gas escapes.  

The baking soda did not react because there was no acid present, but if you add a little acid like vinegar or lemon juice then you will get a reaction that also produces carbon dioxide gas- in fact, lots of gas bubbles and foam!  You may have done this reaction before to make the famous vinegar and baking soda volcano!

Chemical reactions like this are used in baking breads, pancakes, cookies and other foods.  When mixed with flour and water to make a dough the gas bubbles are trapped inside and cause the dough to inflate like a balloon or rise.  That's what happened in the third cup when you added flour.  ​This is called leavening, and ingredients like baking powder or baking soda are call leavening agents.  Baking this dough at high temperature in an oven causes the flour molecules to lock together into a firm solid structure giving us something good to eat!  Meanwhile the carbon dioxide bubbles eventually pop and the gas escapes, leaving behind the tiny little holes we see in baked goods.
​

Some recipes use baking soda instead of baking powder because there is some other ingredient already present that provides the acid needed to produce the gas.  Some recipes even use both baking soda and baking powder to produce carbon dioxide at different times during the baking.  

Most baking powder used today is "Double Acting Baking Powder".  It contains two different acids, one which reacts as soon as the water is added and a second acid that doesn't react until it reaches a certain high temperature.  This causes the dough to rise twice- once when it is first mixed then again during baking in the oven.

You can continue this activity in a tasty way with a simple homemade pancake recipe (see link below), and make it into a real experiment by making some pancakes without the baking powder and baking soda.  How do these pancakes compare to the normal ones?  What if you leave out one of the other ingredients? 

Pizza dough and some other baked goods use a very different ingredient- yeast- to make the dough rise.  Yeasts are actually tiny living organisms called fungi that "eat" sugars and "burp" carbon dioxide gas.  Check out the references below if you would like to experiment with yeast.

What purpose do the various ingredients serve in baking?:

• https://kidpillar.com/science-of-baking-for-kids/
• https://washingtonparent.com/teach-kids-science-through-baking/
• http://www.bakingscience.com

Try a pancake science recipe and experiment:

• https://science-u.org/experiments/pancake-science.html

Other baking science experiments:

• https://www.sciencebuddies.org/science-fair-projects/project-ideas/experiment-with-baking

More baking Soda experiments:

• https://babbledabbledo.com/5-easy-baking-soda-science-projects-your-kids-will-love/
• https://www.steampoweredfamily.com/activities/baking-soda-and-vinegar-experiments/

Yeast science and baking experiments:

• https://kidsdiscover.com/teacherresources/science-of-yeast-for-kids/
• https://www.education.com/science-fair/article/biology_foamy/
• https://www.nationalgeographic.com/history/article/funky-science-yeast-gassy-microbe-behind-coronavirus-pandemic-bread

​

​¿Alguna vez te has preguntado qué hace que la masa de harina se eleve o por qué hay muchos pequeños agujeros dentro de tu pan o panqueques? ¿Y cuál es la diferencia entre bicarbonato de sodio y levadura en polvo? Bueno, estás de suerte porque de eso se trata este experimento.

Coming soon.

Coming soon.

1. Pour some heavy whipping cream into a small jar or plastic container.  For just yourself one or two tablespoons of cream is fine, so be sure to use a very small jar.  If your jar is a larger you can use more, but either way, fill the jar only about half full so you have plenty of room. 
2. Make sure the lid is closed tightly, then shake the jar vigorously.  Use slow, deliberate strokes, almost like you are trying to throw the jar as hard as you can but then stopping your arm suddenly (don't let go!)  The harder you shake, the quicker you will make your butter. 
3. At first you should hear (and feel) the cream sloshing back and forth with each stroke, but after a minute or two you won't hear or feel anything moving inside.  If you like, carefully open the lid a little and peek inside. You should see a thick, creamy white foam.  This is whipped cream- taste a little with your fingertip if you like (of course there is no sugar, so it won't be sweet). 
4. Carefully replace the lid, making sure it is very tight and won't leak, and continue shaking as before.  It feels like nothing is happening, but stick with it.
5. After a few more minutes you will finally hear a liquid begin to slosh around again, and this time you should also feel a thud as something solid slams against the jar.  Shake it a few more times very hard.
6. Carefully open the lid and look inside.  You should see a clump or perhaps a ball of solid butter as well as a thin milky liquid. The butter may be white or yellow.  The liquid is buttermilk. Taste a little of the buttermilk if you like.
7. Carefully pour off all of the buttermilk into another jar or cup if you want to save it for cooking or baking (buttermilk pancakes or biscuits), otherwise just pour it down the sink.  Use your lid as you pour to make sure you don't lose the butter you've worked so hard to make.
8. Add cold water to the jar of butter (about 3/4 full), tightly close the lid and shake it vigorously for about a minute to rinse your butter.  This time you don't need to shake slow and hard, normal shaking is fine. 
9. Carefully open the lid and pour off all the water as before.  Add more cold water and repeat one or two more times until the rinse water is clear.  If you like, you can also use your knife or popsicle stick to stir and knead the butter to rinse it even more thoroughly.

Once you finish rinsing your butter, remove all the water and taste it on some bread or a cracker.  Most butter you find in the grocery store has salt added, but your butter is unsalted (sometimes called sweet butter).  If you don't like the taste, add a pinch of salt.
​
​

Additional Optional Experimental Procedure:

You can also make your own real whipped cream.

1. Chill your of heavy whipping cream in the refrigerator (or even the freezer for an hour or so) so that it is very cold. 
2. Pour one or two cups of chilled cream into a small mixing bowl.
3. Add about 1/4 cup of powdered sugar per cup of cream.  You may also want to add a little vanilla extract or lemon juice for flavor.
4. Use a wire whisk or electric mixer to whip the cream very quickly for a minute or two or until nice and fluffy.  Don't over-whip it or you will get butter again!
5. Taste your whipped cream!​​

Butter is very interesting scientifically.  We  used cream to make butter, but where does cream come from?  Cream comes from cows.  It is part of the milk that a cow gives.  It has a lot of fat in it.  Fat occurs in pieces called molecules.  These molecules like to stick together in big clumps, but at the dairy they homogenized the milk to keep the fat and everything else all mixed up well.  When you shake the cream, however, the molecules which were floating around start sticking to each other.  When enough of them stick together they won't float or stay mixed up any more and you have butter!

​

Try using cold heavy whipping cream to make butter.  Try warm cream.  Does it take more or less shaking to get to butter?  How do you think temperature affects this process?  If you like these milk science activities, you can also try our Milk Fireworks experiment, as well as making cottage cheese and glue (see link below) from milk.

Others versions of this activity:

• https://www.sfi.ie/site-files/primary-science/media/pdfs/col/sci_at_home_make_butter.pdf
• http://www.sciencebuddies.org/science-fair-projects/project_ideas/FoodSci_p050.shtml#summary
  
• http://foodformyfamily.com/recipes/food-science-camp-how-to-make-butter
• http://www.makeandtakes.com/edible-science-experiment-making-butter-whipped-cream
• http://www.scientificamerican.com/article/bring-science-home-butter-emulsion/

Experiment with the temperature of the cream:

• http://www.scientificamerican.com/article/bring-science-home-shaking-butter/

Learn more about milk chemistry:

• https://www.uoguelph.ca/foodscience/book-page/milk-structure

What is homogenized milk?:

• milklife.com/articles/nutrition/what-homogenized-milk

Whipped cream as a science fair project:

• https://www.sciencebuddies.org/science-fair-projects/project-ideas/FoodSci_p022/cooking-food-science/fresh-whipped-cream-that-lasts#summary
• http://observationalgastrophysics.blogspot.com/2010/03/by-naveen-whipped-cream-has-been-on-my.html

What happens when whipped cream comes out of a can?:

• https://science.nasa.gov/science-news/science-at-nasa/2008/25apr_cvx2/​

You can also make glue from milk:

• http://www.science-sparks.com/2012/02/06/make-glue-from-milk/

​

1. Open a Pampers or other brand of disposable diaper and inspect.  Compare to a cloth diaper or towel and a sponge.
2. Place the diapers and sponge on paper plates, newspaper or a plastic bag spread out like a table cloth.  Add some water to each.  How much can each one absorb?
3. To understand why the disposable diaper can hold so much more water, place a new dry disposable diaper on a paper plate, newspaper or garbage bag (some people like to do this step with the diaper inside the garbage bag).  Using scissors, carefully cut through the cloth-like inside layer and peel it open to reveal the cottony fibers inside.
4. Squeeze and rub the cotton with your fingers.  You should feel some powder between the fibers.
5. Separate the white powder from the cotton fibers by rubbing and peeling.  Collect as much as you can and place it into a small cup.
6. Add water to the powder in the cup, a little at a time and observe what happens.  Keep adding water until no more can be absorbed.  Are you amazed at how much water it absorbs without dripping?

​

Why is this powder so good at absorbing water?   Polyacrylic acid is a polymer made from the monomer acrylic acid.  Polymer molecules are kind of like long chain made up of lots of identical links (the monomers).  Polyacrylic acid chains contain thousands of monomer units, as well as cross-linking between different molecule chains, which makes them kind of tangle together.  Most polymers, such as polyethylene and polystyrene (used in trash bags, plastic bottles, and Styrofoam®, for example) are hydrophobic, meaning they repel water.  Polyacrylic acid, however, is very hydrophilic - it attracts water- because of the carboxylic acid groups (COOH) in the polymer, which can hydrogen-bond to water molecules.  The cross-linking also helps trap lots of bonded water molecules inside the tangled chains.

You can make this activity more colorful by adding a few drops of food coloring to the water.  Also try adding some table salt to the water.  What happens?  [Table salt is sodium chloride (NaCl) and the chloride ions will bond with the SAP and prevent water molecules from doing so.]

If you place the wet polymer on a towel or napkin and allow it to dry out for a few days it will dehydrate and shrink back to almost its original powder form and can be used over an over again.

Polyacrylic acid, often just called baby diaper polymer or super absorbent polymer (SAP), comes in many forms and has many other applications.  SAP is often used to clean up hazardous waste spills- even more hazardous than what ends up in a baby diaper!  Just sprinkle the dry powder on the spilled liquid and then sweep or vacuum it up.  You can also find SAP in moisture-control potting soils at a garden store.  If you over-water your plants the SAP will absorb the excess water.  As the soil dries the SAP dehydrates and the excess water returns to the soil, maintaining just the right amount or moisture for the plant to thrive.  You can also buy headbands and neckbands that contain SAP inside, after you wet them the water evaporates slowly and keeps you cool for a long time (see the reference link below to make your own!)

You can buy Instant Snow powder from many stores online (see references below). Instant snow is exactly the same material, it's just ground up into a much finer powder. This causes it to form smaller molecular structures and puff up instantly when it absorbs water, giving it the look and feel of real snow.  It's often used in movies when they want snow in a scene without the need for cold temperatures- and the wet mess when it melts!

Orbeez and other water beads are clear spheres and other fun shapes made from the same polyacrylic acid SAP material, but prepared a little differently to form the shapes you see when they absorb water.  Typical Orbeez spheres start as 3 or 4 mm beads, but can grow to more than 1" in diameter as they absorb water. Because they are composed almost entirely of water when fully grown, they are essentially invisible in a bowl of water (as long as both the spheres and the liquid water are clean).  Water is water.  The index of refraction (a measure of how light bends as it passes through a material) of the liquid water is the same as the water in the sphere, so light rays are not refracted as they pass from the water in the bowl to the water in the beads, and the spheres are therefore almost completely indistinguishable from the rest of the water.  They also bounce (but can break if you bounce them too hard) and act as little magnifying glasses.  Just as with the baby diaper polymer, you can add food colors to make colored Orbeez, and if you let them dry they will shrink back down to little beads that you can use over and over again.

The science of sodium polyacrylate and SAP's:

• https://en.wikipedia.org/wiki/Sodium_polyacrylate
• https://m2polymer.com/cross-linked-sodium-polyacrylate

Here are some other ways to do this experiment:

• https://www.stevespanglerscience.com/lab/experiments/baby-diaper-secret-vanishing-water/
• https://www.scientificamerican.com/article/diapers-what-keeps-babies-and-astronauts-from-springing-a-leak/

This video from Science Beyond at the St. Louis Science Center shows you the secret behind one of our most popular demonstrations:

• https://www.youtube.com/watch?v=8giiZjOOwsU

Fun with Instant Snow powder:

• https://www.stevespanglerscience.com/lab/experiments/insta-snow-ideas/

Orbeez!:

• https://mayatoys.net/pages/orbeez

Make your own cooling headband or neck bandana with SAP:

• https://www.ehow.com/how_5247874_make-icy-neck-wraps-headbands.html
• https://www.instructables.com/id/Sew-Very-Useful-Neck-Cooler/

1. It's much easier to make giant bubbles if there is no wind, but if there is a breeze, stand with your back to the wind.  Be prepared to turn your body if the wind changes direction.  
2. Holding the end of a wand handle in each hand, bring your hands close together so that the cords are touching and dangling straight down in a straight line.
3. Carefully dip the cords into your soap bucket, trying not to tangle them.  If the cords are dry (i.e. the first time you use your wand) you may want to let them soak in the soap solution for several seconds so they can absorb plenty of water.
4. Slowly lift your wand straight up and out of the soap solution, keeping your hands close together and the cords touching.
5. Holding your hands as high as you can, slowly open the wand completely by moving your hands apart.  If there is no wind, slowly walk backwards to create enough air flow to start blowing a bubble.
6. To release and launch your bubble so that it can float away, slowly close your wand by moving your hands close together again.
7. If your bubble pops, try again.  Making really big bubbles takes practice, but it's lots of fun while you're learning!

​

Did you know that water molecules are actually very sticky?  You've probably seen them clinging to lots of surfaces like walls, windows and tables.  When one material sticks to another we call it adhesion, and water molecules adhere or stick to many other materials, but they also like to stick to other water molecules.  When a material sticks to itself we call it cohesion.  If there is no good surface around for water to stick to it's perfectly happy sticking to itself by pulling on several other water molecules nearby.  In fact, each water molecule pulls so hard on the others around it that all of the water tries to pull itself into one tight spherical ball if it can't find anything else easier to stick to.  This force is sometimes called surface tension.  Pour some water onto a freshly waxed car or tabletop and it forms lots of little droplets or "beads" because it can't stick as well to the waxy surface (check the video link at the end to see what water does on the International Space Station).   If you pour it on most other surfaces, however, it will spread out if it can stick to those surfaces.

Okay, so what's all this have to do with soap bubbles?  A bubble is like a balloon, with a thin film or skin on the outside surrounding and trapping air (or some other gas) inside.  Water doesn't stick to air though, leaving only other water molecules for it to stick to, but the surface tension of water, or the force with which it pulls on other nearby water molecules, is so strong that it will form small beads full of water (like raindrops) rather than stretching into a thin film.  If we want to stretch water into a thin skin to make a bubble we need to add something else that it would rather stick to, and that's exactly what soap does.  Soaps and detergents are usually long snake-like molecules with one end (let's call it the head) that likes to grab or pull on water molecules while the other end (tail) likes to get as far away from water as possible (or if possible grab something very different like oil or grease, which, by the way, is what makes them so good at cleaning dirt).  

The head ends of soap molecules in your bubble solution grab onto water molecules, but since their tail ends want to get out of the water at the same time, they can only grab one side so that their tail ends can remain in the air.  Other soap molecules can also grab onto the same water molecules but from the opposite side, while also keeping their tail ends in the air.  This leaves the water molecules free to grab some other water molecules, but only in a region where there is no soap, forming a thin three-layer film skin.  You can think of these three layers sort of like a peanut butter sandwich, where the pieces of bread on the top and bottom are the soap layers and the peanut butter inside is the water.  The surface tension of the water layer inside gives the skin of your bubble its strength, while the soap layers above and below weaken the surface tension just enough to allow the water to stretch out into a thin film so that you can blow a bubble.  Materials like soap that reduce the surface tension of water (or other liquids) in this way are called surfactants.

The soap-water-soap film may be strong enough to form a skin of a bubble but it's also very, very thin- thinner than the hair on your head- so there is a limit to how big a bubble you can make with just the cohesive force of water holding it together.  Making it any bigger and the skin will break, popping the bubble.  The guar gum (or cornstarch) you added to the water gives it extra strength to make even bigger bubbles.  The baking powder also helps by controlling pH or acidity of the solution.  You may have seen some soap bubble recipes that add glycerine to the soap, which works by slowing the evaporation of water (although most bubble experts agree that recipes like ours work much better).  Reference links at the end explain in more detail how these ingredients work.  

Try blowing a small bubble inside one of your big bubbles.  To do this get as close as you can to the big bubble without touching it, then gently blow a puff of air into the wall of the bubble (see the video).

Why do bubbles pop?  Remember that the skin of a soap bubble is very thin, and it's only the water layer which really holds the bubble together as the soap layers on either side actually weaken the water's cohesive forces or surface tension.  As the layer of water evaporates the skin of the bubble gets thinner and thinner until the water molecules can no longer hold onto each other and the bubble pops.  Do you think your bubbles would last longer on a hot and dry day, or a cool and humid day?

​Of course a bubble also pops when you touch it- that is if you touch it with your dry finger or something else that draws the water out of its film just like evaporation does.  If you dip your finger or hand into the soap solution you should be able to carefully push it through the skin of the bubble and pull it back out without popping it.  You can even catch and hold a bubble in your hand (as long as your hand is completely wet- touch it with any dry skin and it will pop.  

How can a triangle or square shaped bubble wand still make spherical (ball-shaped) bubbles?  Once you release your bubble from the wand you may have noticed that it quickly formed a more  spherical shape.  This is because a sphere is the most stable shape for a bubble, allowing it to enclose the most air while using the least amount of soap (mathematicians might say enclosing the maximum volume with the minimum surface area).  Huge bubbles have a large amount of water in their skins, however, and as gravity pulls on this water (as well as any wind blowing on the bubble) the relatively heavy skin gets tugged quite a bit, which is why the bubble wobbles and changes shape a bit as it moves, but it still tries to remain mostly spherical.

Did you also notice how colorful your bubbles are (look at the photo above)?   In fact, the different colors form rainbow-like stripes that circle around the bubble (although the colors here are formed in a different way than they are in a rainbow).  These colored stripes are called interference fringes and caused by light rays reflecting off the thin soap-water-soap film of the bubble.  Some light rays reflect off the outside surface of the film and back to your eyes while others pass through this surface, into the film itself, and then reflect off the inside surface and then back to your eyes.  When these various light rays recombine on the way to your eyes we say that they interfere with each other.  This also happens when light rays strike a pane of window glass, but the soap film of the bubble is much, much thinner.  In fact, the thickness of the soap film is close to the wavelengths of light, so that this interference creates colored bands as the thickness of the film changes, which is why the colors change as the bubble slowly evaporates and its skin gets thinner (check out the references at the end to learn more about the physics of light).  Gravity also pulls the water in the bubble downward, so that it's skin is thicker near the bottom.  Thus the fringes or bands of color indicate changes in film thickness similar to how the lines on a contour map indicate elevation changes.  

Just about everything you ever wanted to know about soap bubbles:

• https://soapbubble.fandom.com/wiki/Soap_Bubble_Wiki
• https://www.exploratorium.edu/search/bubbles
• https://soapbubble.dk/en/articles
• https://www.popularmechanics.com/science/a30781401/bubble-math/
• https://arstechnica.com/science/2020/02/physicists-determine-the-optimal-soap-recipe-for-blowing-gigantic-bubbles/

How does soap work, and what is the difference between soap and detergent?:

• https://www.thoughtco.com/how-dos-soap-clean-606146
• https://sciencetrends.com/science-behind-soap-works-make-clean/
• https://explorationclean.org/science

Experiments and other activities with surface tension and soap:

• https://www.scienceworld.ca/resource/catch-bubble/​
• http://www.planet-science.com/categories/under-11s/chemistry-chaos/2011/06/soap---how-does-it-get-things-clean.aspx
• https://www.york.ac.uk/res/sots/activities/soapysci.htm
• https://www.teachengineering.org/lessons/view/duk_surfacetensionunit_less1
• https://www.homesciencetools.com/article/how-to-make-super-bubbles-science-project/

Surface tension of water in space:

• https://mashable.com/2015/10/13/water-blob-space/

Why are bubbles round?:

• https://www.scienceabc.com/pure-sciences/why-are-bubbles-round.html
• https://brilliant.org/wiki/math-of-soap-bubbles-and-honeycombs/

Colors in soap bubbles (and rainbows, just for fun):

• https://www.exploratorium.edu/ronh/bubbles/bubble_colors.html
• https://www.explainthatstuff.com/thin-film-interference.html
• https://micro.magnet.fsu.edu/primer/java/interference/soapbubbles/
• https://science.howstuffworks.com/nature/climate-weather/storms/rainbow2.htm
• https://en.wikipedia.org/wiki/Rainbow
• https://www.rookieparenting.com/make-your-own-rainbow-science-experiment/

Alternative Lava Lamp experiments:

• https://sciencebob.com/blobs-in-a-bottle-2/   (Lava Lamp bottle)
• https://youtu.be/XGgC-S9trD4   (uses salt instead of Alka-Seltzer)

How real Lava Lamps work:

• https://home.howstuffworks.com/lava-lamp.htm

​More about the differences between and oil and water molecules:

• https://www.thoughtco.com/why-oil-and-water-dont-mix-609193
• https://www.thoughtco.com/examples-of-polar-and-nonpolar-molecules-608516
• https://www.scientificamerican.com/article/mix-it-up-with-oil-and-water/

Try some cool density column experiments:

• https://www.stevespanglerscience.com/lab/experiments/density-tower-magic-with-science/
• https://www.stevespanglerscience.com/lab/experiments/oil-and-water/

More about density and buoyancy:

• https://gosciencegirls.com/density-science-for-kids/
• https://mocomi.com/buoyancy/
• https://sciencing.com/teach-buoyancy-grade-school-children-8159938.html
• https://www.khanacademy.org/science/physics/fluids/buoyant-force-and-archimedes-principle/a/buoyant-force-and-archimedes-principle-article

More cool buoyancy experiments:

• https://funlearningforkids.com/dancing-raisins-science-experiment-kids/
• ​https://www.coolscience.org/cool-physics/cartesian-divers  (our Cartesian Divers experiment)

You may have heard someone say that water and oil don't mix.  The molecules (the arrangement of atoms that make up these chemicals) that make up water are very different from molecules that make chemicals like vegetable oil.  Water molecules (or H2O) attract other water molecules and oil molecules can (weakly) attract other oil molecules, but water molecules strongly repel oil molecules, kind of like the way magnets repel each other if you point the north pole of one towards the south pole of the other.  Thus when you add oil to water they will separate into different layers, and the oil layer will float to the surface because oil is less dense than water.  This is the scientific term which means that a cup of water has more mass (and is therefore heavier) than the same cup filled with oil.  The force that causes the oil to float above the water layer is called the buoyant force or just buoyancy.

Since the food coloring is dissolved in water, it also will not mix with oil and sinks to the bottom of your cup.  When you gently pour the oil and color droplets from your cup onto the surface of the large container they first mix with the rest of the oil floating on the surface and the color droplets start to sink.  As they reach the bottom of the oil layer they cling there for a few seconds until they can finally break through into the water below.  Once they make it into the water the food color droplets can begin to dissolve, and because they are just slightly more dense that the rest of the water (the food coloring chemicals give it a little more mass) they slowly sink and create the beautiful color streaks that look sort of like fireworks exploding in slow motion!

What difference does it make if you use hot water instead of cold water?  For a bigger "explosion", try carefully adding a drop of food color directly to the oil puddle on the surface, but don't get too much color in the water or you won't be able to see what's happening.

You can learn more about density and buoyancy by making a density column, where several different (usually colorful) liquids are carefully poured into a tall container where they separate into many layers.  Check out the links below to try this experiment for yourself.

There are several other fun activities and experiments which demonstrate buoyancy, like the Cartesian Diver bottle and Dancing Raisins.  See the links below to have some fun.

More about the differences between and oil and water molecules:

1. https://www.thoughtco.com/why-oil-and-water-dont-mix-609193
2. https://www.thoughtco.com/examples-of-polar-and-nonpolar-molecules-608516
3. https://www.scientificamerican.com/article/mix-it-up-with-oil-and-water/

Try some cool density column experiments:

1. https://www.stevespanglerscience.com/lab/experiments/density-tower-magic-with-science/
2. https://www.stevespanglerscience.com/lab/experiments/oil-and-water/

More about buoyancy:

1. https://mocomi.com/buoyancy/
2. https://sciencing.com/teach-buoyancy-grade-school-children-8159938.html
3. https://www.khanacademy.org/science/physics/fluids/buoyant-force-and-archimedes-principle/a/buoyant-force-and-archimedes-principle-article

Try some cool buoyancy experiments:

1. https://funlearningforkids.com/dancing-raisins-science-experiment-kids/
2. http://www.sciencemadesimple.co.uk/activity-blogs/ketchup_diver
   
3. https://www.kiwico.com/diy/Science-Projects-for-Kids/3/project/Cartesian-Diver/2649
4. https://sciencebob.com/make-a-cartesian-diver/
5. https://www.wikihow.com/Make-a-Spinning-Cartesian-Diver

​

There are two versions of this experiment - Mentos and Diet Coke vs. Mentos and other diet sodas and Mentos and Diet Coke vs. other candies and Diet Coke.  The reason that there are two versions of this experiment is that scientists usually only change one thing (called a variable) at a time.  So, one version changes the soda that is used, and the other version changes the candy that is used.

Version 1 - Mentos and Diet Coke vs. Mentos and other diet sodas

1. Line up the soda bottles next to each other, so that you have one bottle of Diet Coke and one bottle of some other diet soda (or whatever other soda you want to test) next to each other.  This way, you can see which one erupts higher.
2. Drop in the same number of Mentos  (4 is a good amount for a two liter bottle) into the Diet Coke and the other bottle of soda at the same time.  Which one goes higher?
3. Repeat with any other sodas that you want to test.  Be sure to have a bottle of Diet Coke to test with each other kind of soda, so that you have something to compare it to.  Scientists call this a control, because we know what will happen with the Diet Coke and Mentos, and we are comparing that to what will happen with other sodas.

​

https://www.youtube.com/watch?v=zGMxEr2AxHM 
This is the Mythbusters episode that deconstructs what happens when you put Mentos in soda.  Parent note: There are a few shots of Kari Byron wearing a swimsuit that are a bit revealing, but other than that, the science explored here is well done and well tested.

https://www.youtube.com/watch?v=fBkbWKFv2pE
The original Eepybird video using Diet Coke and Mentos, which some people say started the craze.

https://www.eepybird.com/featured-video/coke-and-mentos-featured-video/science-of-coke-mentos 
More explanation from Eepybird.

https://www.acs.org/content/acs/en/education/whatischemistry/adventures-in-chemistry/experiments/mentos-diet-coke.html
Explanation from the American Chemical Society.

https://www.stevespanglerscience.com/lab/experiments/original-mentos-diet-coke-geyser/
Steve Spangler has some ideas about how to take this further, as well.

http://www.appstate.edu/~coffeyts/DietCokeandMentos.pdf
A bona fide scientific study of what is happening and why.

https://www.scientificamerican.com/article/why-does-a-shaken-soda-fi/
https://www.scienceabc.com/pure-sciences/why-a-soft-drink-bottle-fizzes-when-opened.html
https://chemistry.stackexchange.com/questions/40502/why-does-soda-pop-after-shaking
https://www.stevespanglerscience.com/lab/experiments/soda-can-shake-up-experiment/
https://www.livescience.com/34159-tap-soda-can-carbonation.html​
https://www.snopes.com/fact-check/on-tap/
More explanations of what happens when you shake a can of soda.  Some people think there is a trick to keep a shaken can from exploding, but others think it's a myth.  Maybe you should try to confirm or bust the myth!  Does this apply to plastic bottles too?

​https://funlearningforkids.com/dancing-raisins-science-experiment-kids/
https://www.thoughtco.com/the-dancing-raisin-science-experiment-2086765
https://www.stevespanglerscience.com/lab/experiments/dancing-raisins-the-bubble-lifter/​
Adding a few raisins to a glass of soda pop is a lot more fun than you may think!