# The Mole - thick Molar Mass A single 12 C atom has a mass...

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The Mole Even tiny samples of chemicals contain huge numbers of atoms, ions or molecules. For convenience sake, some kind of reference for a collection of a large number of these objects would be very useful (e.g. a "dozen" is a reference to a collection of 12 objects). In chemistry we use a unit called a mole (abbreviated mol ). A mole is defined as the amount of matter that contains as many objects as the number of atoms in exactly 12 grams of 12 C. Various experiments have determined that this number is. .. 6.0221367 x 10 23 This is usually abbreviated to simply 6.02 x 10 23 , and is known as Avogadro's number . One mole of atoms, volkswagens, people, etc. contains 6.02 x 10 23 of these objects. Just how big is this number? One mole of marbles spread over the earth would result in a layer three miles
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Unformatted text preview: thick. Molar Mass A single 12 C atom has a mass of 12 amu . A single 24 Mg atom has a mass of 24 amu , or twice the mass of a 12 C atom. Thus, one mole of 24 Mg atoms should have twice the mass as one mole of 12 C atoms. Since one mole of 12 C atoms weighs 12 grams (by definition), one mole of 24 Mg atoms must weigh 24 grams. Note that the mass of one atom in atomic mass units (amu) is numerically equal to the mass of one mole of the same atoms in grams (g). The mass in grams of 1 mole (mol) of a substance is called its molar mass . The molar mass (in grams) of any substance is always numerically equal to its formula weight (in amu). One H 2 O molecule weighs 18.0 amu; 1 mol of H 2 O weighs 18.0 grams One NaCl ion pair weighs 58.5 amu; 1 mol of NaCl weighs 58.5 grams...
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