Sodium alginate (Say it like you say algae!) is a substance found in the cell walls of brown algae, including seaweeds and kelp. Its rubbery, gel-like consistency may be important for the flexibility of seaweed, which gets tossed around on ocean waves.
Here on dry land, you can use sodium alginate to make edible balloon-like blobs that are liquid in the middle. We can thank scientists for this delicious project, since they discovered that a chemical reaction between sodium alginate and calcium causes the alginate to polymerize, or form a gel. In this experiment, the gel forms on the outside of a sodium alginate blob, where the chemical reaction is taking place. The inside of the blob remains liquid!
No heat is required for this experiment, making it safe and fun for all ages!
Sodium alginate and calcium lactate can be tricky to find at the grocery store, so you’ll probably have to order them online. But they’re not very expensive, and you’ll have lots of fun playing with them!
-a blender or hand blender (parental supervision required for small children)
-1/2 tsp sodium alginate
-2 tsp calcium lactate
-flavored drink drops, like Kool-Aid or Tang (optional)
-squeeze bottle or syringe for popping boba*
You can make these with juice, but if there is any calcium in the juice, you may end up with foam in your blender, since it may start to polymerize the sodium alginate when you blend it in.
- Add 1 and 1/2 cup water (or calcium-free juice) to the blender.
- To the water, add 1/2 tsp. sodium alginate.
- Blend for about a minute, and let rest for 15 or 20 minutes, or until the bubbles are gone.
- If you want to add flavor, divide the sodium alginate solution into small containers and stir in the flavor, like a squirt of Kool-Aid liquid.
- Add 4 cups of water to a clean, clear glass bowl or container.
- To the water, add 2 tsp. calcium lactate and mix until completely dissolved. This is your calcium lactate “bath.”
- To make edible water balloons, fill a spoon, like a tablespoon, with the sodium alginate solution, and slowly lower it down into the calcium lactate bath. You’ll see a gel begin to form. Gently turn the spoon so the sodium alginate falls off the spoon and into the calcium lactate.
- After about 30 seconds, you’ll be able to see a pale blob in the water. Leave it there for three or four minutes. You can make several edible balloons at once.
- When the blobs are ready, use a spoon to carefully remove them from the bath and put them in a clean bowl of water for a few seconds to rinse them off.
- Put your edible balloons on a plate and taste them. What do you think?
- *To make popping boba, add the fruit-flavored sodium alginate to a squeeze bottle or syringe. Drip the flavored sodium alginate into the calcium lactate as fairly large drops. It may take some practice to get uniform drops of the size you desire. When they’re solid enough to remove from the calcium lactate, rinse them gently and add them to your favorite drink. A small sieve works well for rinsing.
Now that you know how to polymerize sodium alginate with calcium, what else could you try? Can you make a foam in the blender? Can you make gummy worms in the bath using the rest of your sodium alginate solution? Can you invent something entirely new??? Try it!
Thank you to Andrew Schloss’s book Amazing (Mostly) Edible Science for the experiment inspiration! Adding the Kool-Aid and Tang drops to add a little flavor and color was our idea! (This blog post was first published on KitchenPantryScientist.com on May 3rd, 2016 and revised to add popping boba July 24th, 2018.)
Want to take egg-dying up a notch the easy way? Marbling eggs using whipped cream and food coloring is a great project for little ones and the results are downright gorgeous!
Hint: Wear disposable glove to prevent your fingers from getting stained.
-hard boiled eggs
-a shallow container
-cool whip or whipped cream
-food coloring (neon, if you can get it)
-a chopstick or toothpick
1. Soak eggs in vinegar for 5 minutes.
2. Spread and smooth a layer of whipped cream across the bottom of the container and drip food coloring all over the whipped cream.
3. Swirl the drips into patterns using a toothpick or chopstick.
4. Remove eggs from vinegar, blot them with a paper towel and roll them through the food coloring. Put them on a plate to dry.
5. When the eggs are dry, wipe the excess whipped cream and color from the shells.
The science behind the fun: Food coloring is an acid dye, so the vinegar (acetic acid) helps it form chemical bonds with the egg shell, dying the egg.
Molecules move from areas of high concentration, where there are lots of other similar molecules, to areas of low concentration, where there are fewer similar molecules in a process called DIFFUSION. When the molecules are evenly spread throughout the space, they have achieved EQUILIBRIUM.
Lots of things can affect how fast molecules diffuse, including temperature. When molecules are heated up, they vibrate faster and move around faster, which helps them reach equilibrium more quickly than they would if it were cold. Diffusion takes place in gases like air, liquids like water, and even solids.
You can watch food coloring molecules diffuse into gelatin (a colloid) when you do this fun, edible Halloween experiment.
Dissolve two 3oz packages of lemon Jell-O in 1 and 1/4 cups of boiling water. (Adult supervision required.) Allow it to cool briefly, and pour it into 2 ice-cube trays with oval-shaped holes. Refrigerate until firm.
Dissolve one 6oz package of Berry Blue Jell-O in 1 and 1/4 cups of boiling water. Cool briefly.
Using the end of a potato peeler or a strawberry corer to hollow out a circle in the middle of each yellow Jell-O “eyeball.” Carve the circle about halfway to the bottom of the gelatin. Use a toothpick or skewer to remove the Jell-O.
Fill the hollow with melted blue gelatin and return to the refrigerator to harden. The blue Jell-O will be the pupil of the eye.
Set ice cube trays containing Jell-O in a casserole dish of hot tap water for 1-2 minutes. Turn upside down in another dish to un-mold and then move your eyeballs to another serving dish.
Use a straw to add Kool-Aid liquid (like Cherry) to the center of each eyeball. Then, use a sharp skewer to draw lines out from the center.
Cover with plastic wrap and let sit for a few hours so the Kool-Aid will start to diffuse.
Add a second color Kool-Aid drops (Like Blue Raspberry) to the center of the eye and repeat.
Cover and refrigerate until ready to serve. The Kool-Aid colors will continue to diffuse into the eyeballs!