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September 12, 2023

What Is a Mole?

The mole is a unit of amount that chemists use to count atoms and molecules in chemical reactions. It is a useful tool because it allows us to determine the mass of a compound rather than counting every atom or molecule individually. This is done by using the stoichiometric coefficients in a balanced chemical equation. The mole is a fundamental concept that helps us understand how chemical equations work.

Unlike familiar units like a pair or a dozen, moles are defined in the scientific world through mathematical relationships and experiments. The official definition of a mole is “an amount of substance that contains the same number of particles as the number of atoms in 0.012 kilograms of carbon-12.” This is called Avogadro’s number, and it is named for the Italian chemist Amedeo Avogadro who lived from 1776 to 1856.

This is a huge number, and it is difficult for many students to grasp. A good analogy is a mole of gray squirrels. One mole of gray squirrels would weigh about 6000 grams, or about the weight of a hardback book. But it is still much more than 12 ounces of pumpkin spice latte.

Despite the fact that a mole is a scientific unit with a well-defined meaning, it is common for chemistry textbooks to misuse the term by attributing it to concepts such as chemical mass or the number of elementary entities. This incorrect interpretation is even present in some prestigious, peer-reviewed chemistry journals.