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# Ch3_Moles - Counting Atoms Mg burns in air(O2 to produce...

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Unformatted text preview: Counting Atoms Mg burns in air (O2) to produce white magnesium oxide, MgO. MgO. Counting Atoms • Chemistry is a quantitative science—we need a “counting unit.” • The MOLE MOLE • 1 mole is the amount of substance that contains as many particles (atoms, 12 molecules) as there are in 12.0 g of 12C. Particles in a Mole Avogadro’s Number Amedeo Avogadro 1776-1856 6.0221367 x 1023 There is Avogadro’s number of There is Avogadro’s number of particles in a mole of any substance. particles in a mole of any substance. How can we figure out how much oxide is produced from a given mass of Mg? Molar Mass 12 1 mol of 12C = 12.00 g of C = 6.022 x 1023 atoms atoms of C 12 12.00 g of 12C is its MOLAR MASS PROBLEM: How many moles PROBLEM: How many moles are represented by 0.200 g of are represented by 0.200 g of Mg? How many atoms? Mg? How many atoms? Mg has a molar mass of 24.3050 g/mol. 0.200 g • 1 mol = 8 .23 x 10 -3 mol 24.31 g How many atoms in this piece of Mg? 8.23 x 10 -3 m ol • 6.022 x 10 23 atoms 1 mol Taking into account all of the isotopes of C, the molar mass of C is 12.011 g/mol g/mol = 4.95 x 10 21 atoms Mg atoms Page 1 ...
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