The Mole, Mass, Amedeo Avogadro

Recap

For most of our high school life, we have been using typical units of measurement such as grams, and occasionally touching on atomic weight. In both chemistry and physics, all atoms have a certain weight to them. The units to these values are called "Atomic Measurement Units", also referred to as "amu"s, "u"s, and "daltons".

Amedeo Avogadro

Amedeo Avacado Avogadro was an 18th century, Italian scientist. He is most famous for his contributions to molecular theory, especially for what is known today as "Avogadro's Law" and "Avogadro's Constant". 

Avogadro's Law, Constant, and the Mole

Avogadro's Law states, that under the same conditions of temperature, volume, and pressure, two different samples of gas will contain the same number of particles. In essence, this means that the number of molecules or atoms of a gas is independent of the size and mass of the gas. 

Avogadro's Constant is currently defined by the International Bureau of Weights and Measures as "the number of Carbon-12 atoms in 12 grams of mass". Currently, this number is approximately 6.022*10²³. To put this into perspective, it is a number about a thirty thousand times larger than today's average computer can hold in a single variable. In base 2, it is approximately 2⁷⁹. The average computer today can store 2⁶⁴bits in a single variable. This number is 100 times the number of stars in the observable universe. If this many pieces of typical paper were stacked on top of each other, it would be tall enough to reach the sun and back (assuming of course the sun doesn't instant incinerate them all), 250 billion times. This astronomically large number, Avogadro's Constant, is the mole unit. 

Mass

In chemistry, there are three kinds of mass describing pure substances. The formula mass, and molecular mass are the mass of ionic and covalent compounds, respectively. Molar mass, on the other hand is the mass of one mole of a pure substance.

For example: Potassium Cyanide, or KCN has 3 elements in it. They are Potassium, Carbon, and Nitrogen.

Their atomic weights are:

1 x Potassium: 39.1u

1 x Carbon: 12.0u

1 x Nitrogen: 14.0u

The sum of this is the formula mass of Potassium Cyanide, 65.9u. This translates to 65.9grams/mol for Potassium Cyanide.

Another example: Water or H₂O, containing Hydrogen and Oxygen

Atomic weights are:

2 x Hydrogen: 2 x 1.0u

1 x Oxygen: 16u

The sum of this is the molecular mass of water, 18.0u. This translates to 18.0grams/mol for water.

Conclusion

The Mole is important for many branches of science, not just for chemistry. This constant number allows for scientists to determine number of atoms and molecules in a given sample with relative certainty.

For us students, it just means that unit conversions are going to become a lot messier.

Here's an amusing video to lighten up your day. Though it has nothing to do with today's topic, except the KEY word: Mole! Enjoy.