Chemistry elementary May 21, 2026

Why Does Vinegar React With Baking Soda?

A fizzy change that makes a gas

A clear cup with vinegar and baking soda bubbling as carbon dioxide gas forms during a chemical reaction

Vinegar reacts with baking soda because they are two substances that change each other when mixed. The bubbles are carbon dioxide gas leaving the liquid. The other new substances are water and a dissolved salt.

Big Idea. NGSS 5-PS1-4 asks students to explain that mixing substances can form new substances, which is what happens when vinegar and baking soda react.

Vinegar and baking soda are common kitchen materials, but together they do something that feels surprising. A spoonful of baking soda sits quietly as a white powder. Vinegar looks like plain liquid. When they touch, foam rises and bubbles pop. That fizz is a sign that new substances are forming. This is not just mixing, like stirring sugar into water. It is a chemical reaction. Vinegar contains acetic acid. Baking soda is sodium bicarbonate. When the acid and the baking soda meet, their tiny particles rearrange. One product is carbon dioxide gas. The gas makes the bubbles that lift the foam. Other products stay in the cup as water and a dissolved salt called sodium acetate. This simple reaction helps students see that matter can change in ways we can observe, measure, and explain.

What is in the cup

A cup of vinegar beside a spoonful of baking soda with simple particle zooms showing liquid acid particles and solid bicarbonate particles — Vinegar and baking soda start as different substances

Vinegar is mostly water, but it also contains a small amount of acetic acid. That acid gives vinegar its sharp smell and sour taste. Baking soda is a solid called sodium bicarbonate. It looks like a white powder because it is made of many tiny grains. Each grain contains particles arranged in a regular way. When the powder is dry, those particles mostly stay put. When vinegar is added, the particles can move through the liquid and meet. The important meeting happens between the acid from vinegar and the bicarbonate from baking soda. They do not just float side by side. They interact and change into different substances. This is why the cup starts to bubble soon after the two materials touch. The fizz begins where the liquid reaches the powder.

The reaction starts when acid particles meet bicarbonate particles.

The fizz is a gas

Carbon dioxide bubbles rising from a vinegar and baking soda mixture and filling a small balloon attached to a bottle — Bubbles show carbon dioxide gas forming

The bubbles are the easiest clue to see. They are not air that was already trapped in the powder. They are mostly carbon dioxide gas made during the reaction. Gas takes up space, so it pushes through the liquid as round bubbles. Many bubbles together make foam. If the reaction happens in a bottle with a balloon on top, the balloon can inflate because the gas has nowhere else to go. That shows that the gas is a real material, even though it is hard to see by itself. Carbon dioxide is the same gas that makes bubbles in soda water. In this reaction, it forms quickly and escapes into the air. The bubbling slows down when one of the starting substances is mostly used up.

Bubbles are evidence that a new gas is being made.

New substances form

A simple reaction diagram showing vinegar and baking soda changing into carbon dioxide bubbles, water, and dissolved sodium acetate — Reactants change into products

A chemical reaction makes new substances from old ones. In this case, vinegar and baking soda change into carbon dioxide, water, and sodium acetate. Sodium acetate is a salt, but not the same salt people usually put on food. It stays dissolved in the water, so students usually do not see it as a solid. The change can be written as a word equation. Acetic acid plus sodium bicarbonate makes carbon dioxide plus water plus sodium acetate. The words help us track what goes in and what comes out. They also remind us that the foam is only one part of the reaction. Some products are easy to see, like the gas bubbles. Some products are hidden in the liquid. Even when we cannot see every product, careful tests and measurements show that they are there.

The reaction makes more than bubbles.

Matter is not lost

Two setups comparing an open cup where gas escapes and a sealed bag that inflates while keeping the gas inside — A closed system keeps the gas in

The foam can make it seem like material is disappearing. It is really moving. Carbon dioxide leaves the liquid and spreads into the air. If the reaction happens in an open cup, some gas escapes, so the cup may have less mass afterward. That does not mean matter was destroyed. It means some matter left the cup. If the same reaction happens inside a closed bag, the gas stays inside. The bag puffs up, but the total mass of the sealed bag stays about the same. This idea connects to conservation of matter. Matter can change form and move from place to place, but it is not created or destroyed in an ordinary chemical reaction. Measuring before and after helps students separate what seems to happen from what the evidence shows.

Lost gas can make mass seem to disappear in an open cup.

Changing the amounts

Three cups with different amounts of baking soda and vinegar producing small, medium, and large amounts of foam — Amounts affect how much gas forms

The amount of fizz depends on how much vinegar and baking soda can react. If there is a lot of vinegar but only a little baking soda, the baking soda may run out first. If there is a lot of baking soda but only a little vinegar, the acid may run out first. The leftover material cannot keep reacting by itself. This is why adding more of one ingredient does not always make more bubbles. Students can test this by keeping one amount the same and changing the other amount. They can compare foam height, balloon size, or mass change in an open cup. A fair test changes only one thing at a time. That makes the results easier to understand. The reaction is simple, but it supports real science practices like measuring, recording data, and using evidence.

More fizz happens only when both reacting materials are available.

Vocabulary

Chemical reaction: A change in which substances become different substances.
Acid: A substance that can react with certain materials, including baking soda. Vinegar contains acetic acid.
Base: A substance that can react with an acid. Baking soda acts as a base in this reaction.
Carbon dioxide: A colorless gas made during the vinegar and baking soda reaction.
Product: A substance made by a chemical reaction.
Conservation of matter: The idea that matter is not created or destroyed during ordinary changes, even when it changes form or location.

In the Classroom

Balloon gas test

20 minutes | Grades 3-5

Place vinegar in a small bottle and baking soda in a balloon. Attach the balloon, tip in the powder, and watch the balloon inflate as carbon dioxide forms. Students compare the balloon before and after to identify evidence of a gas.

Open cup and sealed bag

30 minutes | Grades 4-5

Run the reaction once in an open cup and once in a sealed plastic bag. Students predict what will happen to the mass in each setup, then measure before and after. The comparison supports conservation of matter.

Fizz amount investigation

35 minutes | Grades 3-5

Keep the vinegar amount the same and change the amount of baking soda in three trials. Students record foam height or balloon size and look for a pattern. Discuss why the fizz stops when one reactant runs out.

Key Takeaways

• Vinegar and baking soda react because acid particles meet bicarbonate particles.
• The fizz is carbon dioxide gas made during the reaction.
• Water and sodium acetate also form, even though they are harder to see.
• Matter is not destroyed when the gas escapes into the air.
• Changing the amounts of vinegar or baking soda can change how much gas forms.

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