Why Does Baking Soda Fizz With Vinegar? Everyday Acid-Base Reactions

Pour a little vinegar onto a spoonful of baking soda and the mixture erupts into foam. It looks like magic, but it is one of the neatest reactions in Class 10 chemistry, and the same chemistry works in your stomach, your toothpaste and your cooking.

This guide explains what is really happening in the glass, places that reaction in the wider family of acid-base reactions, and shows where you meet it every day. It ends with a safe home activity and a few questions to test yourself.

What Is Really Happening in the Glass

The cast

The reaction

When an acid meets a metal hydrogencarbonate, the products are always a salt, water and carbon dioxide gas:

CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑

The salt is sodium acetate, and the bubbles are carbon dioxide. Count the atoms on each side and you will find the equation is already balanced. Behind the scenes, the hydrogencarbonate first becomes carbonic acid, and that acid breaks down at once into water and carbon dioxide, which is why the foam appears so fast.

Proving the gas

Pass the gas through lime water, which is a calcium hydroxide solution. It turns milky because calcium carbonate forms:

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

That milky test is how a student proves in the laboratory that the gas is carbon dioxide, and it is a favourite exam question. For a similar kitchen reaction, see why vinegar fizzes on chalk.

Acid Meets Base: The Family of Reactions

The vinegar-and-baking-soda fizz is one member of a family. Learn the pattern, and you can predict the products of reactions you have never seen.

Is the fizz a neutralisation?

It is closely related, because an acid is being used up and a salt and water form. Strictly, though, textbooks use the word neutralisation for acid + base → salt + water. The baking soda fizz belongs to the acid + hydrogencarbonate group, which also gives off carbon dioxide. In an exam, name the group your question is about.

Why vinegar is gentle

Acetic acid is a weak acid, so it reacts slowly enough to watch. A strong acid like hydrochloric acid would react far more vigorously, which is one reason lab work needs care. To see how strength is measured, read about how strong acid or base solutions are, and for the full list of chemical properties see these notes on the chemical properties of acids and bases.

Five Places You Meet Them Every Day

Antacids and the stomach

Your stomach makes hydrochloric acid to digest food. When there is too much, you feel acidity. Antacids contain mild bases, such as magnesium hydroxide (milk of magnesia), which neutralise the excess acid:

Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O

Toothpaste and tooth decay

Bacteria in the mouth break down sugar and make acids. When the pH of the mouth falls below about 5.5, tooth enamel starts to corrode. Toothpastes are basic, so they neutralise the acid and slow the damage.

Ant stings

An ant sting injects methanoic acid, which causes the burning pain. Rubbing a mild base such as a paste of baking soda on the spot neutralises the acid and gives relief.

Farm soil

Soil that is too acidic harms many crops. Farmers add basic substances such as lime (calcium oxide or calcium hydroxide) to neutralise the extra acid, and the acid-base reaction does the rest.

Cakes, dhokla and fizzy powders

Baking powder is a mixture of baking soda and a mild edible acid such as tartaric acid. When it gets wet, the two react and release carbon dioxide, which makes the batter rise and become soft and spongy. Fizzy fruit salts and effervescent antacid powders use the same idea with a different mild acid.

For a broader list of familiar chemicals, see these common acids, bases and salts in chemistry.

Try It Safely

Two safe kitchen activities

1. The balloon test. Put a few spoons of vinegar into a small bottle. Put a spoonful of baking soda into a balloon, stretch the balloon over the bottle’s neck, and lift it so the soda falls in. The balloon inflates, which shows that a gas is being produced.
2. A red cabbage indicator. Soak chopped red cabbage in warm water and strain it. Add a few drops to vinegar and then to a baking soda solution. The colours differ, with the acid turning pinkish-red and the base turning bluish-green, because a natural indicator changes colour with acids and bases.

Use small quantities, keep the bottle open at the neck apart from the balloon, and ask an adult to help.

To balance reactions faster, read about common mistakes in balancing chemical equations and how to identify the type of chemical reaction. Also check out why we add acid to water and never water to acid.

Acids and Bases Through the Classes

Acids, Bases and Salts is Chapter 2 in both the CBSE and Karnataka SSLC Class 10 textbooks. It covers indicators, the reactions of acids and bases, pH and the uses of salts such as baking soda and washing soda. See these Class 10 notes with reactions and the chapter MCQs with answers.

In Class 11 Chemistry the same ideas return as ionic equilibrium, with the ionization of acids and bases, the pH scale and buffers. Equilibrium is part of the NEET and JEE Main chemistry syllabi, and this guide to acid-base chemistry for NEET shows how it is used there. Portions of the chapter, such as the uses of particular salts, have been trimmed or rearranged in some years, so confirm the current ones with your board.

Frequently Asked Questions

Q1. Why does baking soda fizz with vinegar?

Vinegar contains acetic acid, which reacts with sodium hydrogencarbonate (baking soda) to form sodium acetate, water and carbon dioxide. The bubbles you see are the carbon dioxide gas.

Q2. What is the chemical equation for baking soda and vinegar?

CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂. The equation is already balanced.

Q3. How do you test that the gas is carbon dioxide?

Pass the gas through lime water, which is a calcium hydroxide solution. It turns milky because calcium carbonate is formed.

Q4. What are some everyday examples of acid-base reactions?

Antacids neutralising excess stomach acid, toothpaste neutralising acids made by mouth bacteria, baking soda soothing an ant sting, lime treating acidic soil, and baking powder making cakes rise are all common examples.

Q5. Is baking soda an acid or a base?

Baking soda, which is sodium hydrogencarbonate, is a mild base. Its solution is slightly basic, which is why it reacts with acids such as vinegar and can neutralise the acid from an ant sting.

Chemistry Is Happening in Your Kitchen

The next time something fizzes, you will know what is going on: an acid is meeting a hydrogencarbonate, salt and water are forming, and carbon dioxide is escaping as bubbles. Once the pattern is clear, antacids, toothpaste and ant stings stop being separate facts and become the same idea in different places.