THE MOLE UNIT

What is a mole? The best answer is that a mole is a certain number of molecules, atoms, electrons , or other specified types of particles." In particular, the 1969 International Committee on Weights and Measures approved the mole (symbol mol in the SI system) as being "the amount of a substance that contains as many elementary entities as there are atoms in 0.012 kg of carbon 12." Thus in the 51 system the mole contains a different number of molecules than it does in the American engineering system . In the SI system a mole has about 6.023 X 1023 molecules; we shall call this a gram mole (symbol g mol) to avoid confusion even though in the SI system of units the official designation is simply mole (abbreviated mol). We can thereby hope to avoid the confusion that could occur with the American engineering system pound 23 mole (abbreviated lb mol) , which has 6.023 X 10 x 453 .6 molecules. Thus a pound mole of a substance has more mass than does a gram mole of the substance.