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December 5 · free experiment

Theo & Tilda’s Christmas Science

Foam Mountain Experiment

Mix baking soda with a few drops of dish soap, pour in vinegar all at once, and a fizzy mountain of foam grows and spills over the bowl. The acid and the base react and make carbon dioxide gas, and the soap traps the bubbles.

  • Age5 and up
  • ValueTeamwork
  • ScienceChemical reactions
  • FlameNone
Get Day 5 free as a PDFHow to do it
  • Ages 3–9
  • Kitchen materials
  • No flame, no heat
  • Tested by a physicist
Real photo from Janka’s lab: the Foam Mountain experiment
NO STOCK PHOTOJanka’s real result
December 5: Theo and Tilda’s Foam Mountain adventure

In short

  • You need: 2–3 tablespoons of baking soda, ½ cup (120 mL) of white vinegar, dish soap, a bowl, a tray and safety goggles.
  • You see: a mountain of foam grows, then spills over the bowl.
  • Why: baking soda and vinegar react and make carbon dioxide, and the dish soap wraps the gas into lasting bubbles.
  • Name: Foam Mountain, a baking soda and vinegar experiment. Day 5 of a 24-day December plan.
Step by step

How do you make Foam Mountain?

Watch baking soda and vinegar build a mountain of foam. Here is everything from the book page, ready for your kitchen table.

What you need

  • 2–3 tbsp baking soda
  • 120 mL (½ cup) white vinegar
  • A few drops of dish soap
  • Pink or turquoise food coloring (optional)
  • Bowl and spoon
  • Tray to catch the foam
  • Safety goggles

Stay close the whole time. In the book, every step that only a grown-up may do is clearly marked.

  1. 1

    Put the bowl on a tray or in the sink, because the foam will spill over. Add 2–3 tbsp baking soda.

  2. 2

    Stir in a few drops of dish soap and, if you like, a little pink or turquoise food coloring.

  3. 3

    Put on safety goggles. Pour about 120 mL (½ cup) of vinegar onto the mixture all at once, then step back a little.

  4. 4

    Watch the foam grow and spill over the bowl! Don’t taste it. If any splashes into your eyes, rinse them with plenty of water.

What’s happening?

Why does it work?

Janka Sára Molnár, physicist

Janka explainsThe same words you’ll find in the book, ready to read aloud.

Baking soda is slightly basic, and vinegar is acidic. When they meet, a chemical reaction starts and makes carbon dioxide gas. Dish soap forms a stretchy skin around the gas bubbles, so they don’t pop right away but pile up into a lasting foam that spills out of the bowl. The fizzing only looks like a volcano erupting: in a real volcano, gases escaping from hot magma cause the eruption.

Science words for little scientists

  • chemical reactionwhen substances meet and change into new ones
  • carbon dioxidethe invisible gas that makes the bubbles in fizzy drinks
  • foamlots of tiny bubbles packed together
The Foam Mountain experiment in Janka’s lab
Theo and Tilda in the story “A Fizzy Foam Mountain”
The story for December 5

A Fizzy Foam Mountain

The sledding hill was still bare, so the elf kids planned a foam mountain for the square. Theo the Science Elf gave out jobs: Bonnie brought the bowl, Tilda the coloring, and Zack the vinegar. In went baking soda, dish soap, and Tilda’s pink and turquoise drops. Zack poured from his bottle. Nothing! It was water. He’d mixed up the bottles. “It didn’t work because of you!” someone yelled. “You had one job!” Theo snapped too. Zack’s ears went red.

How does it end? The whole story, the activity page and four more days are in the free sampler.

Read the whole story free
The value of the dayTeamwork

What does it mean?

On a good team, we don’t blame each other when things go wrong. We look for a fix together. Mistakes are shared, and so is success.

Why is it important?

Anyone can make a mistake, even the best of us. If we stick together after a failure, everyone dares to try, and we get further.

Mini mission for the week

If something goes wrong in a group game this week, don’t look for who’s to blame. Try again together!

After the experiment

Let’s talk about it

Ready-made questions link the story’s value to your child’s own life. There are no wrong answers, only curious ones.

  • Why did Theo call Zack back when he had snapped at him too?

  • How do you think Zack felt when everyone blamed him? And when Theo called him back?

  • Would you like to be like Theo, who held the team together? When have you worked together like that?

  • What happens at preschool or school when someone spoils a group game? What could you do?

Tilda’s tip: No foam at first? Don’t look for someone to blame. Check what’s missing together!

Look inside

This is how Day 5 looks in the book

Real pages from the free sampler. Tap a page to see it big, then read it on a tablet or print it at home.

The story page for December 5: A Fizzy Foam Mountain
Story page
The experiment page for December 5: Foam Mountain
Experiment page

Day 5 is one of 5 free days. The full book has 51.

Get the 5 free daysSee the full book
The free 5 days

Your first five December adventures

  1. Day 1December 1Milk Fireworks
  2. Day 2December 2Magic Snow
  3. Day 3December 3Holiday Lava Lamp
  4. PreviousDecember 4Candy Rainbow
  5. You are hereDecember 5Foam Mountain
  6. 19In the bookDecember 6–24See the whole plan
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Free sampler

Can we try it first?

Of course! The first 5 days of the December plan are yours for free. Try them at home or with your group, and see if your little scientist asks for Day 6.

  • 5 cozy stories
  • 5 kitchen experiments
  • 5 activity pages
  • A note from Janka
  • A cover with your name and the 5 experiments

No printer needed. Open it on a tablet or phone and start today.

The cover of the free sampler: your first 5 days of December, with a mini adventure trail
FREE5 days
  1. December 1: Milk Fireworks1Milk Fireworks
  2. December 2: Magic Snow2Magic Snow
  3. December 3: Lava Lamp3Lava Lamp
  4. December 4: Candy Rainbow4Candy Rainbow
  5. December 5: Foam Mountain5Foam Mountain
Launch prices

How much does it cost? Less than a hot cocoa.

Launch prices until December 24. Your files are ready the moment you check out.

The cover of Theo and Tilda’s Christmas Science Adventure

The Book

129 printable pages

$11.99Regular price $14.99

less than 50¢ a day in December

Get the book
  • 51 stories and 51 experiments
  • 24-day December plan
  • Story words and science words
  • Stampable two-page adventure map
  • Contents, learning index, and certificate
Best value
The cover of the Theo and Tilda Christmas Activity Pack

Book + Activity Pack

Everything in the book, plus 60+ pages of FUN

$13.99Regular price $17.99

less than 60¢ a day in December

Get the bundle
  • The complete book
  • Coloring pages, mazes, and word games
  • Puppets, ornaments, and bookmarks
  • Kindness advent calendar
  • Word cards and value talk cards

No printer? No problem. Read it on any tablet, phone or computer, and print only the pages you love.

One price for everyone. A parent can print it for Advent at home, and a preschool teacher can bring it to her group. One purchase covers one family, or one teacher with their own group or class.

Prices in US dollars. Any sales tax or VAT is calculated at checkout.

Questions and answers

Foam Mountain: what parents ask

Short answers from Janka, the physicist who tested the experiment in her own lab.

Still wondering?

Write to Janka. She reads every email herself.

molnar.janka.sara@funtasztikus-tudomany.hu
Get the book · $11.99Try 5 days free
What happens when baking soda meets vinegar?

Baking soda is slightly basic and vinegar is acidic. When they meet, a chemical reaction starts and makes carbon dioxide gas. The dish soap wraps the gas in stretchy bubbles, so they pile up into foam.

Is it a volcano?

It only looks like one. In a real volcano, gases escaping from hot magma cause the eruption. Here the bubbles come from a cold reaction in a bowl.

How much baking soda and vinegar do I need?

2–3 tablespoons of baking soda and about ½ cup (120 mL) of white vinegar, poured in all at once. A few drops of dish soap make the foam last.

Is it safe?

Yes, with a grown-up. The recommended age is 5 and up. Everyone wears safety goggles, children step back a little when the vinegar goes in, and nobody tastes the foam. If any splashes into the eyes, rinse them with plenty of water.

Which story goes with Foam Mountain?

“A Fizzy Foam Mountain”, the story for December 5. Its value is teamwork: the mountain grows best when everyone has a job.