Week 7: What is a mole?

According to this article, “the mole was determined by experiments, where the standard temperature chosen is 25 degrees C. and the pressure on the gas is chosen as one atmosphere or 760 millimeters of mercury. While there is nothing special about these values, the temperature is about average room temperature and the pressure is average atmospheric pressure at sea level. It is only important that everyone doing the experiments uses the same temperature and the same pressure (or makes appropriate corrections). It was eventually shown that a Gram Molecular Weight of a gas, at standard temperature and pressure, would occupy 22.4 liters of volume. Or saying it the other way, 22.4 liters of a gas at standard temperature and pressure contains the number of molecules that weigh as much as the molecular weight of the gas expressed in grams.”

The next logical question to ask is: "What is that number of molecules that weighs in grams what the molecule weighs in relative atomic weight units?" The number, named after Avogadro, is 6.0221367 x 10 exp23, is a very large number, indeed. This is the number of molecules in 22.4 liters of gas at standard temperature and pressure, but it is also the number of molecules in a sample of any material that weighs as much as the molecular weight of the substance expressed in grams. A Gram Molecular Weight of any substance contains Avogadro's number of molecules.
The idea of a MOLE is a very useful concept, since it allows you to relate the weight of the material to the number of molecules in that weight. The mole idea also allows you to combine equal amounts (numbers of molecules in each) of two compounds. If you have a gram molecular weight of one compound and a gram molecular weight of another compound, there are equal numbers of molecules in the two weights. If you wanted the two compounds to combine so there was one molecule of each material available to combine with every molecule of the other compound, then mixing the two gram molecular weights would create this result.

"The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilograms of carbon 12." As so defined, the mole became a key unit (fundamental unit) of the International System of Weights and Measures (aka Metric System) adopted worldwide. As such the mole is technical unit used mainly by chemists, chemical engineers, ceramic engineers, and potters…for potters, the mole is an essential notion of glaze technology, a division of applied chemistry, or chemical engineering, ceramics branch. Who knew!