Bicarbonate of soda and vinegar: the science behind it

My kids love seeing the fizzing reaction between bicarbonate of soda and vinegar, and indeed I have done a lot of experiments and sensory play using these ingredients. But what exactly is the science behind the exciting reaction?

Bicarbonate of soda, or baking soda in the US, is the chemical sodium bicarbonate. Sodium bicarbonate is an alkali. This means it has a pH of greater than 7 (where pure water has a pH equal to 7). In scientific terms, this means that when it dissolves in water, it yields hydroxide ions OH. Vinegar contains acetic acid which, as the name suggests, is an acid. This means it has a pH of less than 7 and when it dissolves in water, it yields hydrogen ions H+.

Sodium bicarbonate and acetic acid react together in an acid-base reaction (base is another word for alkali). This first produces carbonic acid and sodium acetate. The carbonic acid then starts to decompose into water and carbon dioxide. Carbon dioxide is a gas, and it is this gas that is released as the ‘bubbles’ or ‘fizz’ of the reaction.

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