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The Mole: A Measurement of Matter OBJECTIVES: Describe how Avogadro’s number is related to a mole of any substance.

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The Mole: A Measurement of Matter OBJECTIVES: Calculate the mass of a mole of any substance.

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What is a Mole? You can measure mass, or volume, or you can count pieces. We measure mass in grams. We measure volume in liters. We count pieces in MOLES.

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Moles (abbreviated: mol) Defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole is 6.02 x 10 23 particles. Treat it like a very large dozen 6.02 x 10 23 is called Avogadro’s number.

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Representative particles The smallest pieces of a substance. For a molecular compound: it is the molecule. For an ionic compound: it is the formula unit (ions). For an element: it is the atom. Remember the 7 diatomic elements (made of molecules)

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Types of questions How many oxygen atoms in the following? CaCO 3 Al 2 (SO 4 ) 3 How many ions in the following? CaCl 2 NaOH Al 2 (SO 4 ) 3

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Types of questions How many molecules of CO 2 are there in 4.56 moles of CO 2 ? How many moles of water is 5.87 x 10 22 molecules? How many atoms of carbon are there in 1.23 moles of C 6 H 12 O 6 ? How many moles is 7.78 x 10 24 formula units of MgCl 2 ?

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Measuring Moles Remember relative atomic mass? The amu was one twelfth the mass of a carbon-12 atom. Since the mole is the number of atoms in 12 grams of carbon-12, the decimal number on the periodic table is also the mass of 1 mole of those atoms in grams.

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Gram Atomic Mass (gam) Equals the mass of 1 mole of an element in grams 12.01 grams of C has the same number of pieces as 1.008 grams of H and 55.85 grams of iron. We can write this as 12.01 g C = 1 mole C We can count things by weighing them.

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Examples How much would 2.34 moles of carbon weigh? How many moles of magnesium is 24.31 g of Mg? How many atoms of lithium is 1.00 g of Li? How much would 3.45 x 10 22 atoms of U weigh?

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What about compounds? in 1 mole of H 2 O molecules there are two moles of H atoms and 1 mole of O atoms To find the mass of one mole of a compound determine the moles of the elements they have Find out how much they would weigh add them up

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What about compounds? What is the mass of one mole of CH 4 ? 1 mole of C = 12.01 g 4 mole of H x 1.01 g = 4.04g 1 mole CH 4 = 12.01 + 4.04 = 16.05g The Gram Molecular Mass (gmm) of CH 4 is 16.05g this is the mass of one mole of a molecular compound.

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Gram Formula Mass (gfm) The mass of one mole of an ionic compound. Calculated the same way as gmm. What is the GFM of Fe 2 O 3 ? 2 moles of Fe x 55.85 g = 111.70 g 3 moles of O x 16.00 g = 48.00 g The GFM = 111.70 g + 48.00 g = 159.70 g

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