Sour, and eager to give something away
What Makes Something an Acid?
Lemon juice, vinegar and the acid in your stomach are all doing the same thing, just with different force.
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Step 1 of 5
An acid gives something away.
Dissolve an acid in water and each molecule lets go of one tiny positively charged particle. Everything acids do — the sour taste, the fizzing, the burning — comes from those loose particles.
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Step 2 of 5
Sour is your tongue detecting them.
Your tongue has receptors that respond to exactly those loose particles. More of them means more sour — which is why lemon juice is sharper than apple juice.
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Step 3 of 5
Alkalis are the exact opposite.
An alkali soaks those particles up instead of giving them out. Mix an acid and an alkali in the right amounts and they cancel out completely, leaving salty water and often some heat.
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Step 4 of 5
Fizzing is a gas escaping.
Acid on chalk, limestone or baking soda pulls them apart and releases a gas. Those bubbles are the acid winning — and it is the same reaction that eats away at old stone buildings.
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Step 5 of 5
Your stomach is strongly acidic on purpose.
Stomach acid is strong enough to attack metal. It kills most of what you swallow and starts breaking food apart — and the stomach protects itself with a constantly renewed layer of slime.
Weak acids are safe and everywhere — vinegar, lemon, fizzy drinks, sour milk. Strong ones are dangerous for the same reason, just more of it.
The short version
An acid hands out a tiny charged particle; that is what tastes sour, fizzes on chalk, and eats into things.
Try it yourself
Put a spoonful of baking soda in a glass and pour vinegar on it. Every bubble is the acid taking it apart.
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