what you'll need
experimental procedure
what's happening
Let’s take a closer look at our crackers. Do they look poofy at all to you? Or are they pretty flat? They should be flat, because we didn’t add any leavening to them. Leavening is the cooking term for any ingredient that will make things that you bake poofy. Things like baking powder and baking soda make bread and cakes rise because they react with other ingredients in the dough to make carbon dioxide bubbles. The holes that we see when we look at a piece of bread are the outsides of those carbon dioxide bubbles. The carbon dioxide escapes into the air, and we have a delicious piece of bread. However, in this case, we didn’t want the crackers to be poofy, so we didn’t put anything in that would make the bubbles. So, our crackers should be flat and delicious! variations and related activities
Coming soon. references and links to more information
Coming soon.
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 You won't believe how easy it is to make your own butter simply by shaking a cup of heavy whipping cream, which comes from milk. Give it a try- and you even get to eat this experiment when you're done! Click tabs below to get started what you'll need
For whipped cream (optional):
Be sure to ask your mom, dad or another adult to help-you can share your butter with them. experimental procedure
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.
what's happening
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!
more detailed explanation
You've probably heard that oil and water don't mix, but milk is in fact a mixture of many different components, including sugars, proteins, fats and yes, water. [Fats and oils are basically similar molecules, also often called lipids, and made of smaller building blocks called fatty acids. Although fat, oil and lipid are often used to refer to fats, "oil" generally refers to a fat that is liquid at normal room temperature and "fat" is solid at room temperature.] The oil or fat in milk can mix with water without separating because they form into little globules sort of like water balloons. The fat is inside a thin skin or membrane which helps attract water somewhat, and because fat is less dense than water, the globules float and form what's called a colloidal suspension or emulsion. The smaller the globules, the easier it is for them to remain emulsified, but if they are too large they will separate and float to the surface. Years ago before milk was homogenized, the fat globules would float to the top and form a layer called the cream, which contained most of the milk's fat. Homogenization breaks up the larger globules into smaller ones, which, along with the milk proteins that then help form a stronger globule membrane, prevent this separation. The cream you buy at the grocery store is separated at the dairy and then homogenized to keep the fat suspended in the liquid. Heavy whipping cream means that it has a very high fat content, 36-40% (normal cream is about 30% fat, while Half & Half is 12% and whole milk 3.5% fat). Butter is essentially pure milk fat.
In our heavy cream, the fat globules are still emulsified, or suspended in the water along with some protein and sugar. If we shake the cream though, the globules will begin to crash into one another and pop or burst their membranes. When this happens the fat molecules spill out and clump together with other fat molecules. At first as this happens the fat traps a lot of air and forms bubbles or foam, which is the whipped cream. The more you shake it, however, the more bubbles pop and the more densely the fat clumps become until they can no longer remain suspended in the water, and they separate completely. This is the butter, and the remaining liquid, mostly water and proteins, is called buttermilk. The butter you make is not only good to eat, but will stay fresh for a long time, especially if it is thoroughly rinsed of all the milk liquid, since the milk can spoil. Adding sugar to the whipped cream not only sweetens and thickens it, but helps prevent the fat bubbles from popping so that it will stay a light fluffy foam much longer. variations and related activities
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. references and links to more information
Others versions of this activity:
Experiment with the temperature of the cream: Learn more about milk chemistry: What is homogenized milk?: Whipped cream as a science fair project:
What happens when whipped cream comes out of a can?: You can also make glue from milk:
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Click and expand the tabs below to get started. What you'll need
experimental procedure
what's happening
Modern disposable baby diapers contain a small amount (4-5 grams) of polyacrylic acid in a powder form (sodium polyacrylate), which is mixed into the fluff in the middle layer of the diaper. The inside layer of the diaper allows water to pass through it into the absorbent middle layer, and the outer layer is waterproof, so both baby and mommy stay dry. Polyacrylic acid can absorb about more than 100 times its own weight in water, which is why an average sized diaper can absorb up to 16 ounces of water. Luckily that's more than a baby usually pees.
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.
Variations and related activities
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. references and links to more information
The science of sodium polyacrylate and SAP's:
Here are some other ways to do this experiment:
This video from Science Beyond at the St. Louis Science Center shows you the secret behind one of our most popular demonstrations: Fun with Instant Snow powder: Orbeez!: Make your own cooling headband or neck bandana with SAP:
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Click and expand the tabs below to get started what you'll need
basic procedure
making giant bubbles
what's happening
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. variations and related activities
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. references and links to more information
Just about everything you ever wanted to know about soap bubbles:
How does soap work, and what is the difference between soap and detergent?:
Experiments and other activities with surface tension and soap:
Surface tension of water in space: Why are bubbles round?:
Colors in soap bubbles (and rainbows, just for fun):
Click and expand the tabs below to get started. What you'll need
experimental procedure
what's happening
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. They are usually plated with a thin layer of another metal like nickel, which makes they appear to be metal, but they are actually a type of ceramic, which is more like glass, so they 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 a mere 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? variations and related activities
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. References and links to more information
Other variations of this experiment:
Why iron is so important for your body:
Which breakfast cereals have the most iron:
Iron and magnetism (ferromagnetism):
The Cheerios Effect (and how it affects bugs that walk on water):
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What you'll need
experimental procedure
what's happening
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, these drops also will not mix with oil and sink to the bottom of your cup where they burst and mix with the water to color it. The solid Alka-Seltzer pieces are more dense than the oil or the water, so they sink all the way to the bottom. As soon as they reach the water they begin to dissolve and a chemical reaction takes place between two of the ingredients that produces carbon dioxide gas bubbles. As these bubbles rise they pull some of the water along with them and have enough buoyancy to rise through the oil layer, but once they reach the surface the bubbles pop and the gas escapes. Now the water droplets are too heavy to float, and they fall back through the oil where they may pick up another gas bubble to rise again. This process resembles the rising and falling bubbles in a Lava Lamp, but it works a little differently. A real Lava Lamp also contains two immiscible liquids (i.e. they don't mix) with different densities, but it uses the energy from a light bulb underneath to warm the lower liquid. As it warms it expands and its density decreases, allowing bubbles to rise up through the upper liquid. As these bubbles float higher (and farther away from the heat source) they cool down, become denser once again, and fall back into the lower layer where the process can repeat. The upper liquid also warms during this process, but it was carefully chosen so that its density does not decrease as much, so that it still provides enough buoyant force to push the bubbles from the lower liquid upwards. See the reference link below for a more detailed explanation. variations and related activities
references and links to more information
Alternative Lava Lamp experiments:
How real Lava Lamps work: More about the differences between and oil and water molecules:
Try some cool density column experiments:
More about buoyancy:
More cool buoyancy experiments:
Click and expand the tabs below to get started. What you'll need
experimental procedure
What's happening
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! variations and related activities
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. references and links to more information
More about the differences between and oil and water molecules:
Try some cool density column experiments:
More about buoyancy:
Try some cool buoyancy experiments:
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