Key concepts
Chemistry
Chemical reaction
Surfactants

Introduction
If you live where there is snow, it can be fun to play in it for a while—but it can get quite chilly. Or maybe you live someplace where it doesn't snow. In this fun activity, you can experience something similar to snow anytime, in the comfort of your own home. You will mix together some common kitchen supplies to make a sculpted object, and then, whenever you decide, you can let your snow creation "melt" away and turn into a white surface. Curious how kitchen chemistry can look like snow? Try this activity and find out!

Background
Just a few common and safe household chemicals—baking soda, vinegar and dishwashing soap—can lead to an interesting project that examines two areas of chemistry.

Vinegar (or diluted acetic acid) combined with baking soda (also called sodium bicarbonate) yields a cascade of two chemical reactions. The end products are carbon dioxide (a gas) and water, in which two chemical products (sodium ions and acetate ions) are dissolved. As you observe this reaction, you see the carbon dioxide gas as bubbles rising to the surface of the liquid and hear a fizzing noise.

Soaps cover a different aspect of chemistry. They contain surfactants, or surface-active agents. These agents reduce the surface tension of the liquid. As such, they assist in the creation of foam. Foam is pockets of air or gas trapped in a thin layer of liquid. Foam does not form on pure water, as water likes to stick together. Air bubbles rising to the water surface push through and escape. Adding surfactants to the water allows the soapy liquid to spread out and trap the air bubbles, so a layer of foam forms.

Usually, air gets trapped when we vigorously move the soapy water. Would the gas produced when vinegar reacts with baking soda get trapped and create foam? Do this activity to find out. And see what you can do with the results!

Materials

  • Two large plastic containers
  • Measuring cup
  • Baking soda
  • Measuring spoons: a teaspoon and a tablespoon
  • Sticky note
  • Pen or pencil
  • Dishwashing soap
  • Vinegar
  • Small waterproof items to decorate your creation (optional)

Preparation

  • Choose a workspace that can get dirty and wet.
  • Write "Soap" on a sticky note and stick it to one of the plastic containers.

Procedure

  • Scoop one cup of baking soda into both plastic containers.
  • Add three tablespoons of water to the container without the sticky note and mix the ingredients together to make a dough. It should feel like play dough. You can add water, small amounts at a time, if the dough is too crumbly, until you reach the right consistency.
  • Have fun molding a snowman, a polar bear or any other critter. Feel free to decorate your creation with waterproof objects. Keep your creation in that container.
  • Now, take the plastic container with the sticky note reading "Soap," and make a second batch of dough using a slightly altered recipe. Add one teaspoon of dishwashing soap to the baking soda, followed by three tablespoons of water. Do you notice the difference in the recipes?
  • Mix the ingredients together to make a dough. You can add water, small amounts at a time, until the dough molds well. Does this dough feel similar or different compared to the other one?
  • Have fun molding a second critter; it could be very similar or quite different from your first creation, but try to make something of similar height and size. Feel free to decorate this creation with waterproof items. Keep your creation in that container.
  • Admire your creations. In the next step, you will melt them in a fun and exciting way: you will pour vinegar over your creations (but don't do it yet)! Can you predict what will happen? Remember that the main ingredient of your dough is baking soda. Did you ever mix baking soda with vinegar before? What happened? Would something similar happen now?
  • Fill your measuring cup with vinegar and pour all of it at once over your first creation. What happens? What do you see and hear? Is it as you expected, or is it different?
  • Fill your measuring cup again with vinegar and pour all the vinegar at once over the other creation. What happens this time? What do you see and hear?
  • What is similar and what is different between the two containers? Do you remember what was different between the two recipes? Would that explain the difference between the observations?
  • Most likely, your critter is partially destroyed and only partially standing. Try something different this time; find out what happens when you pour water over your critters. What do you think will happen?
  • Rinse your measuring cup and fill it with water. Pour all of it at once over whatever is left of your first creation. What happens? Is it as exciting as pouring vinegar over it?
  • Fill the measuring cup again with water. Can you predict what will happen if you pour it, all at once, over whatever is left of your second creation? Go ahead. Was your prediction right?
  • If your creations are still partially standing, keep trying out different actions. What happens if you pour slowly? Take some dough in your hand and pour vinegar or water over it as you hold it over the container. How does it feel?
  • Extra: Repeat the activity, using different liquids to pour over the creations, such as lemon juice or soda or milk. Before you pour, what do you think will happen—and why?

Observations and results
Did you see both creations fizzing as soon as vinegar touched them? When vinegar comes in contact with baking soda, a cascade of two chemical reactions takes place. The result is carbon dioxide gas—a product of the reactions—bubbling up in a water solution. The bubbles create the fizz and sizzling sound.

Whatever was left of your first creation (the one without the soap) was probably standing in a pool of a bubbling watery solution, where bubbles burst open as they reached the liquid surface. This was probably different for your other container. The leftover of the second creation—which had a dishwashing soap mixed into the dough—was probably surrounded by a layer of white foam. Detergents have surfactants in them. These allow soapy solutions to spread out. The bubbles created in the chemical reaction still rose to the surface, but now, the soapy solution spread out and trapped the bubbles forming a foam.

As water does not react with baking soda, pouring water over your creations probably just washed away some dough without any sizzling, fizzing or foaming.

Other acids, such as those in lemon juice, can also be used to make the dough fizz. Neutral solutions (such as water) or base solutions (such as milk) will not cause a chemical reaction. Neither creation will start fizzing when these are poured over them.

Cleanup
Pour your liquid solutions down the drain. Any solid dough can be thrown in the trash.

More to explore
Sudsy Science: Creating Homemade Bath Bombs, from Scientific American
Blow the Best Bubbles, from Scientific American
Science Activities for All Ages, from Science Buddies

This activity brought to you in partnership with Science Buddies

Science Buddies