The Mole

Although moles are fascinating mammals and my children love to watch them course through the tunnels at the local zoo, this article does not focus on the animal but rather the SI base unit that measures the amount of a substance.

The mole, abbreviated mol, is defined as the number of carbon atoms in exactly 12g of carbon-12.  The number of carbon atoms in 1 mole of carbon is equal to 6.02 x 10^23 atoms (^ indicates an exponent is following).  You have most likely encountered this number already in your studies and years later after you are done with formal education, you will be able to recite this number (as well as the quadratic formula) without batting an eye.  6.02 x 10^23 is Avogadro’s number.

Avogadro’s number lets us assign an exact quantity to a mole of anything.  A mole of cars, a mole of money, or even a mole of water all contain 6.02 x 10^23  cars, dollars, or water molecules.

Avogadro’s number is a key conversion factor to be used in those pesky factor-label problems.  You can use this ratio with either the number of particles or mol in the denominator depending on whether you want to convert particles to moles or moles to particles.

Another useful tool about the mole is that if you look on the periodic table, the molar mass of any element is equal to its atomic mass.  So if we want to know how many grams are in one mole of fluorine, we simply look up the atomic mass in the periodic table.  19g of fluorine equals 1 mol of fluorine.

Molar mass is another conversion factor to use when you might be asked to convert the number of particles to mass or vice versa.  Check out the sample problem below!

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