A gas being made
Why Does Baking Soda Fizz?
Acid and baking soda react to produce carbon dioxide, and the bubbles are the new gas.
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Step 1 of 5
The gas is made, not released.
Fizzy drinks release gas that was already dissolved. Here the carbon dioxide is genuinely created by the reaction.
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Step 2 of 5
It needs an acid to react with.
Vinegar, lemon juice or buttermilk will do. In dry powder with nothing acidic, baking soda does essentially nothing.
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Step 3 of 5
Atoms are rearranged into new substances.
The acid and the soda swap parts, producing water, a salt and carbon dioxide. Nothing is created or destroyed — only reassembled.
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Step 4 of 5
Gas takes up far more room.
The carbon dioxide occupies hundreds of times the volume of the ingredients that made it, which is why it foams up so dramatically.
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Step 5 of 5
Baking uses the same trick.
The gas is trapped in dough and expands in the oven, leaving the bubbles that make bread and cakes light instead of dense.
Self-raising flour already contains a dry acid, so it only needs liquid to start reacting.
The short version
Baking soda fizzes because it reacts with acid to create carbon dioxide, and the new gas takes far more space.
Try it yourself
Put baking soda in a balloon and vinegar in a bottle, fit them together and tip. The balloon inflates itself.
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