The Acetic Acid and Sodium Bicarbonate Reaction Explained

When acetic acid reacts with sodium bicarbonate, the products are carbon dioxide, water, and sodium acetate. The carbon dioxide escapes as bubbles, causing the familiar fizz.

The balanced equation is:

CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂

The equation shows a one-to-one ratio: one mole of acetic acid reacts with one mole of sodium bicarbonate. The reaction occurs when vinegar, which contains acetic acid dissolved in water, is mixed with baking soda, which is sodium bicarbonate.

What happens in the reaction

Acetic acid donates a hydrogen ion (H⁺) to the bicarbonate ion (HCO₃⁻). This forms carbonic acid, which quickly breaks down into water and carbon dioxide gas. Sodium and acetate ions remain in the liquid, where they form dissolved sodium acetate.

The escaping carbon dioxide makes the bubbles. The gas can also produce foam as bubbles collect at the liquid’s surface. The fizz slows when one of the reactants has been used up. If baking soda is left over, there is no longer enough acid to react with it. If vinegar is left over, the liquid remains acidic.

The reaction does not require equal amounts by volume or by mass. The one-to-one ratio refers to moles, or numbers of particles. Since vinegar is a dilute solution and baking soda is a solid, equal spoonfuls do not provide equal amounts of acetic acid and sodium bicarbonate.

Acetic acid is a weak acid, meaning it does not fully separate into ions in water. That does not prevent it from reacting with bicarbonate. As the reaction consumes acid, more acetic acid molecules can ionize, allowing the process to continue while reactants remain available.

One example: vinegar and baking soda

Add baking soda to a small amount of vinegar in an open cup. The mixture fizzes as carbon dioxide forms and escapes. When the bubbling stops, the cup contains water and dissolved sodium acetate, along with any excess reactant.

The exact amount of gas depends on how much acetic acid and sodium bicarbonate are present. Household vinegar is a dilute solution, so its label or concentration would be needed to calculate a precise amount. The balanced equation gives the proportions needed for a calculation, but the reaction’s visible fizz alone does not reveal how much of either ingredient was used.

Keep the container open or leave its lid loose. Carbon dioxide can build pressure in a sealed container as it forms.

What affects the fizz

The quantity of each reactant determines how much carbon dioxide can form. Once the available acid or bicarbonate is consumed, the reaction slows and stops. Adding more of the reactant that is already in excess will not produce more gas.

Temperature and mixing can affect how quickly the reaction proceeds and how the bubbles escape. Stirring helps the ingredients mix, while the shape of the container can change how foam collects. These factors affect what you see, not the products shown in the balanced equation.

What remains after bubbling stops

Sodium acetate stays dissolved in the water. If the water evaporates, the salt can remain as a solid. The final liquid may taste less sour than the vinegar because some of its acetic acid has reacted. Its exact taste depends on whether acid or bicarbonate remains in excess.

Sodium bicarbonate is described in its PubChem entry, and sodium acetate is described in its PubChem entry. Acetic acid is covered in its PubChem entry.

Key Takeaways

• Acetic acid reacts with sodium bicarbonate to produce carbon dioxide, water, and sodium acetate.
• Carbon dioxide escaping from the liquid causes the fizz.
• The balanced reaction uses one mole of acetic acid for each mole of sodium bicarbonate.
• The fizz stops when one reactant is used up; any excess of the other remains.
• Keep the reaction in an open or vented container so gas does not build pressure.