# 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: Describe how Avogadro’s number is related to a mole of any substance.

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

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.

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.

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)

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

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 ?

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.

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.

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?

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

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.

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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