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# National Mole Day

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Author: carolyn fruin
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October 23 from 6:02 am to 6:02 pm, Mole Day is celebrated. No, it has nothing to do with a brown furry creature with big paws and tiny eyes. A mole is a large number of somethings. Like a dozen is 12 somethings, a mole is 602,000,000,000,000,000,000,000 (6.02 x 1023) somethings.

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Tutorial

## Happy Mole Day!

Fun Mole Day Classroom Activities

Send a Mole Day greeting to a mole of friends.

Drink a glass of molasses milk (201g [7.1 oz ] of C6H12NNaO3S = 1 mole) at 6:02am & pm.

Bake and eat 6.02 molasses cookies.

Drink 1 mole of H2O (18 g or 0.63oz) of water at 6:02 am.

Ask people to guess how many moles you have in a brown paper bag.

Design or buy a mole day t-shirt

## The Mole

by Jonathan Atteberry

How on Earth did chemists settle on such a seemingly arbitrary figure for Avogadro's number? To understand how it was derived, we have to first tackle the concept of the atomic mass unit (amu). The atomic mass unit is defined as 1/12 of the mass of one atom of carbon-12 (the most common isotope of carbon). Here's why that's neat: Carbon-12 has six protons, six electrons and six neutrons, and because electrons have very little mass, 1/12 of the mass of one carbon-12 atom is very close to the mass of a single proton or a single neutron. The atomic weights of elements (those numbers you see below the elements on the periodic table) are expressed in terms of atomic mass units as well. For instance, hydrogen has, on average, an atomic weight of 1.00794 amu.

Unfortunately, chemists don’t have a scale that can measure atomic mass units, and they certainly don’t have the ability to measure a single atom or molecule at a time to carry out a reaction. Since different atoms weigh different amounts, chemists had to find a way to bridge the gap between the invisible world of atoms and molecules and the practical world of chemistry laboratories filled with scales that measure in grams. In order to do this, they created a relationship between the atomic mass unit and the gram, and that relationship looks like this:

1 amu = 1/6.0221415 x 1023 grams

This relationship means that if we had Avogadro's number, or one mole, of carbon-12 atoms (which has an atomic weight of 12 amu by definition), that sample of carbon-12 would weigh exactly 12 grams. Chemists use this relationship to easily convert between the measurable unit of a gram and the invisible unit of moles, of atoms or molecules.

Now that we know how Avogadro's number comes in handy, we need to examine one last question: How did chemists determine how many atoms are in a mole in the first place? The first rough estimate came courtesy of physicist Robert Millikan, who measured the charge of an electron. The charge of a mole of electrons, called a Faraday, was already known by the time Millikan made his discovery.

Dividing a Faraday by the charge of an electron, then, gives us Avogadro's number.

## Avogadro’s Contributions to the Scientific Field

In 1811 Avogadro theorized that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. He further established that relative molecular weights of any two gases are similar to the ratio of the densities of the two gases under the constant conditions of temperature and pressure. His suggestion is now known as the Avogadro’s principle. He also cleverly reasoned that simple gases were not formed of solitary atoms but were instead compound molecules of two or more atoms. (Avogadro did not actually use the word atom; at the time the words atom and molecule were used almost interchangeably. He talked about three kinds of “molecules,” including an “elementary molecule”—what we would call an atom.) Thus Avogadro was able to resolve the confusion that Dalton and others had encountered regarding atoms and molecules at that time.

Avogadro’s findings were almost completely neglected until it was forcefully presented by Stanislao Cannizarro at the Karlsruhe Conference in 1860. He demonstrated that Avogadro’s Principle was not only helpful to determine molar masses, but also, indirectly, atomic masses. Avogadro’s work was mainly rejected before due to earlier established conviction that chemical combination occurred due to the similarity between unlike elements. After the electrical discoveries of Galvani and Volta, this similarity was in general attributed to the attraction between unlike charges.

The number of molecules in one mole is now called Avogadro’s number taking the value of 6.0221367 x 1023. The number was not actually determined by Avogadro himself. It was given his name due to his outstanding contribution to the development of molecular theory.

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