3.2.1 The Mole

What is a Mole?

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A mole is a special unit in chemistry used to count particles like atoms or molecules. One mole of any substance contains 6.02 × 10²³ particles. This huge number is called Avogadro's number, named after the scientist Amedeo Avogadro who helped come up with the concept.

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Why Do We Use Moles? Just like you might ask for a dozen eggs (meaning 12 eggs), chemists use moles to count atoms and molecules because they're so tiny that counting them individually would be impossible.

How Much Does a Mole Weigh?

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The mass of one mole of a substance is equal to its relative atomic mass (Ar) or relative formula mass (Mr) in grams.

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Example: One mole of carbon $(C)$ weighs 12 grams because the Ar of carbon is 12. One mole of water $(H₂O)$ weighs 18 grams because the Mr of water is 18 (2×1 + 16).

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