Volcano Science, Homemade Edition

For this week in wacky science, I'll be teaching kids how to make volcanoes with vinegar and baking soda. I'm already shuddering at the mess this could create.

Unfortunately, kids are good at picking up when you fall into unknown knowledge territory. They'll proceed to fill up your time teaching as you flounder for an explanation with their own rendition of memes and kid-talk, and you curse yourself for thinking you can be the slightest bit lazy in researching explanations for wacky science things.

The good news is that it seems like the science is short and simple. The bad news is I will then make it longer and a little more complicated, because I want to go the extra mile for the students if given the chance.

At first glance, it really is kinda simple. Just the production of carbonic acid by combining baking soda with vinegar. Carbonic acid is very unstable, so it instantly breaks apart into water and carbon dioxide and gas, which under pressure from the vessel it's in - bottle, jug, soda can, or what-have-you - will create a fizzing explosion in its escape.

Then you look at why this happens. Baking soda is the generic term for the compound sodium bicarbonate, which is a base. Vinegar is acetic acid, which obviously is an acid. If something is ticking in your head, it's because in chemistry you hear the question a lot: what happens when you combine an acid and a base?

You get a neutralization reaction, producing water and a salt.

This is because acids and bases are basically two extremes of a short spectrum of pH levels. Acids have a positively-charged hydrogen ion to give away, and bases can either accept this positively-charged hydrogen ion or give away their whole negatively-charged hydroxide ion. The hydroxide ion is just the buddies oxygen and one hydrogen, but oxygen prefers the stability of two hydrogen ions which is why it has a negative charge. It's trying to catch another hydrogen, because opposites attract in the case of organic chemistry.

Either way, acid spits out one hydrogen ion and the base either takes or spits out their own ions, and those ions get together to form dihydrogen monoxide, aka water.

If it was just hydrogen and hydroxide ions, the simple output would be water. But the hydrogen ion and the hydroxide ions break off from something, and that something combines to form a salt.

Salts in chemistry are not quite the salts you find in your kitchen. In the technical chemistry jargon you find in a textbook, they are any ionic compound made from a cation and an anion, usually formed from an acid-base reaction. The salt may be sodium chloride or calcium sulfate or potassium nitrate; it depends on whatever ingredients you put into the pot that make the stew.

And just to be thorough: these somethings combine because they are also charged, negative from the acid and positive from the base, and once again opposites attract.

Why opposites attract comes from the domain of quantum physics, which I can explain some other time at the request of my blog readers. They have my number.

The special thing with sodium bicarbonate and acetic acid that creates the volcano eruption is that the product of water is technically secondary. The first reaction between the acid - giving the positively-charged hydrogen ion - and the base - offering the negatively-charged bicarbonate ion - is the creation of carbonic acid.

Carbonic acid is unstable. In chemistry, this doesn't mean an explosion like the splitting of an atom. It's not that dramatic. It just means that the compound will quickly decompose, breaking apart to become carbon dioxide and water. Those two compounds are in a lesser-energy state, so they're energetically favorable. Welcome to quantum physics via Le Châtelier’s principle.

This decomposition reaction is reversible, so in the vessel containing this event you'd be seeing carbonic acid constantly forming and breaking down. And because of energy states and quantum physics, it's mostly going to be carbon dioxide and water rather than a large amount of carbonic acid.

This is why I say the water is a bit of a secondary product. The process of producing water and salt from this acid-base reaction includes a hidden step, so this is really a three-step reaction than a simple two-step reaction. That's what makes it so exciting to show to kids!

Now, this is where you can relate the chemical explosion to a volcanic eruption: the pressure level.

In a volcano, the pressure comes from deep underground. At some point in digging into a volcano, you're going to meet molten rock (magma). That molten rock is a soup, a liquid full of gases and other dissolved materials. Those gases can include water, carbon dioxide, and sulfur dioxide.

From the weight of overlying rock that is a freaking volcano (or in some cases, a mountain, which can be a dormant volcano), there is very high pressure. Gases stay dissolved, swimming in the magma.

The magma is not a stationary thing, either. It increases. Given pressure, more heat, and a dash of water (such as from tectonic plate movements), surrounding rock will break down to join the hot soup. The water helps in that it lowers that surrounding rock's melting point (the temperature required for melting) so it breaks down sooner.

Since liquids are less dense than solids (with the exception of ice), the magma becomes buoyant. It rises to the surface.

There's an allegory for Icarus somewhere here, because the higher magma comes to the surface of the volcano, the more the pressure drops. The weight of overlying rock decreases. There's more space for the magma. To put it even more simply, there's less stuff on your head, so there's less pressure. And that pressure drop makes the gases in the magma soup become less soluble.

The gases meet up. They cluster. They form bubbles in the magma. Bubbles of gas make that magma less dense and more buoyant, and so it rises even more. This becomes a positive feedback loop, where pressure is hitting the magma at both ends - from uptop with the hard rock cap, and from below/middle with the gas bubbles. There's external pressure and internal pressure, and one of these has got to go.

Eventually there's no more rock to melt at the top of the volcano. And if there has been a lot of internal pressure - a lot of gas bubbles - then the explosion is going to be huge and fast.

Ladies and gentlemen, the eruption of a volcano.

That build up of gas and pressure is the same thing happening with the homemade volcano. The carbon dioxide gas from the carbonic acid can't easily recombine to form carbonic acid again. In the way of energy states and physics, once it becomes gas it can't go back.

This gas builds up in the small bottle, creating that important internal pressure. The small bottle's hole at the top is a mercy; if it weren't there, the bottle itself would explode from the pressure. So like the volcano, the bottle erupts. The gas leaves the vessel with the water, making bubbles and a foamy medium. The salt? It's dissolved in the water or left behind in the bottle. It's not important.

This explosion from gas buildup and internalized pressure is what leaves you wary of soda after you shake the can and before it opens. It's what makes bottle rockets.

So this homemade volcano science is what helps us understand fluid dynamics, gas-liquid interactions, natural hazards, pressure dynamics, and environmental and chemical engineering. It's the bridging of theory and observation, turning textbook knowledge into experience and practical applications.

There's a lot of things for the kids to learn here, but I think I most hope to convey to them the importance of experience and practicality when it comes to scientific knowledge. I learned it a little too late myself, realizing the value of experience and practicality in my undergraduate college (essay about that in my thesis on my website). If I can let them know the importance of being aware in the moment of the doing, of what's going on, of turning memorized facts into visualized action, then I can rest well.

I can know I did a good job teaching this week.

But best laid plans and all that. I'll let you know what happened in this week's Captain's Log.

Citations for the science (not in alphabetical order):

1. “Make a Volcano – Science Project | NASA JPL Education.” NASA JPL Education, 2024, www.jpl.nasa.gov/edu/resources/project/make-a-volcano/.
2. “Magma’s Role in the Rock Cycle.” Nationalgeographic.org, 2024, education.nationalgeographic.org/resource/magma-role-rock-cycle/.‌
3. Physical Geology – Maricopa.edu. “Molten Materials.” Open.Maricopa.edu, 3.9 years ago, https://open.maricopa.edu/physicalgeologymaricopa/chapter/5-2-molten-materials/.
4. “4.03: Magma Generation.” An Introduction to Geology, LibreTexts, 25 Aug. 2025, https://geo.libretexts.org/Bookshelves/Geology/Book%3A_An_Introduction_to_Geology_(Johnson_Affolter_Inkenbrandt_and_Mosher)/04%3A_Igneous_Processes_and_Volcanoes/4.03%3A_Magma_Generation
5. “Flux Melting.” Wikipedia, https://en.wikipedia.org/wiki/Flux_melting
6. “Magma.” Wikipedia, https://en.wikipedia.org/wiki/Magma
7. “Volcanic Arc.” Wikipedia, https://en.wikipedia.org/wiki/Volcanic_arc
8. “Neutralization (chemistry).” Wikipedia, https://en.wikipedia.org/wiki/Neutralization_(chemistry)
9. “Acid and Base Neutralization.” LibreTexts Chemistry, chem.libretexts.org, 30 Jan. 2025, https://chem.libretexts.org/Courses/American_River_College/CHEM_309%3A_Applied_Chemistry_for_the_Health_Sciences/08%3A_Acids_and_Bases_Equilibrium_and_Buffers/8.01%3A_Acid_and_Base_Neutralization
10. “Neutralization Reactions.” Introductory Chemistry — Lumen Learning, https://courses.lumenlearning.com/suny-introductory-chemistry/chapter/neutralization-reactions/
11. “Acid‑Base Neutralization Reactions.” ChemistryTalk.org, https://chemistrytalk.org/acid-base-neutralization-reaction/
12. Kobayashi, Reina et al. “Quantitative Estimation of Phospholipid Molecules Desorbed from a Microbubble Surface under Ultrasound Irradiation.” Scientific Reports, vol. 13, article 13693, 22 Aug. 2023, https://www.nature.com/articles/s41598-023-40823-0
13. Lu, Shirui et al. “Mechanistic Insights and Therapeutic Delivery through Micro/Nanobubble‑Assisted Ultrasound.” Pharmaceutics, vol. 14, issue 3, 22 Feb. 2022, https://pubmed.ncbi.nlm.nih.gov/35335857/
14. Chang, Jin Ho & Kim, Hyuncheol. “Microbubbles Used for Contrast Enhanced Ultrasound and Theragnosis: A Review of Principles to Applications.” Biomedical Engineering Letters, Springer, https://link.springer.com/article/10.1007/s13534-017-0016-5
15. “Biosurfactants for Microbubble Preparation and Application.” PMC, https://pubmed.ncbi.nlm.nih.gov/3039964/
16. “Baking Soda And Vinegar Volcano Kitchen Science Experiment.” Science Fun, https://www.sciencefun.org/kidszone/experiments/baking-soda-and-vinegar-volcano-kitchen-science-experiment/