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The Mole

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What is a mole? Mole (mol) – a counting unit. Similar to a dozen. 1 dozen is always 12. Chemists use moles to count very small objects, like atoms and molecules. 1 mole = 6.022x10 23 particles. 6.022x10 23 = 602.2 billion trillion Avogadro’s Number (N)

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Amadeo Avogadro (1776-1856)

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How Big Is Avogadro’s Number? If you had Avogadro’s number of dollars: you’d be 12.8 trillion times richer than Bill Gates. you could match the entire world’s gross domestic product 11 billion times. you could pay every person on Earth almost 90 trillion dollars (as of September 2008).

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Counting by Weighing – A Marble Analogy Imagine being asked to count a small handful of green marbles. Easy, right?

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Counting by Weighing – A Marble Analogy Now imagine being asked to count the marbles in a large paper bag. You could count the marbles individually (tedious!) or... You could find the mass of one marble, then weigh the bag of marbles and get a good estimate of how many marbles the bag contains.

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Counting by Weighing – A Marble Analogy Could you count the marbles in the back of a dump truck? You’d have to count them exclusively by weighing. (Don’t forget to subtract the mass of the truck!)

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Counting by Weighing Like the marbles in the dump truck, atoms are too numerous to count individually. But we can estimate their numbers by weighing.

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Molar Mass Molar mass (MM) – the mass of one mole of a substance in grams. For elements, the MM is equal in number to the atomic mass.

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Molar Mass C 6 12.01 1 carbon atom = 12.01 daltons (average) 1 mol C = 12.01 grams

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Molar Mass What is the mass (in grams) of 4.60 mol C? 4.60 mol C mol C g C 1 12.01 = 55.2 g C

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Molar Mass How many atoms are in 4.60 mol C? 4.60 mol C mol C atoms 1 6.022x10 23 = 2.77x10 24 atoms

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Molar Mass Are 4.60 moles of carbon, 55.2 grams of carbon, and 2.77x10 24 atoms of carbon all the same amount? Yes!

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Molar Mass How many moles are in 16.00 g He? 16.00 g He g He mol He 4.00 1 = 4.00 mol He

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Molar Mass of Compounds To find the MM of a compound: Add the MMs of its elements. EXAMPLE: The MM of H 2 O is: 2 x H = 2 x 1.01 g/mol = 2.02 g/mol 1 x O = 1 x 16.00 g/mol = 16.00 g/mol TOTAL = 18.02 g/mol 1 mol of H 2 O masses 18.02 g.

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Molar Mass of Compounds The MM of Na 2 SO 4 is: 2 x Na = 2 x 22.99 g/mol = 45.98 g/mol 1 x S = 1 x 32.07 g/mol = 32.07 g/mol 4 x O = 4 x 16.00 g/mol = 64.00 g/mol TOTAL = 142.05 g/mol 1 mol of Na 2 SO 4 masses 142.05 g.

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Molar Mass of Compounds The MM of Ca(NO 3 ) 2 is: 1 x Ca = 1 x 40.08 g/mol = 40.08 g/mol 2 x N = 2 x 14.01 g/mol = 28.02 g/mol 6 x O = 6 x 16.00 g/mol = 96.00 g/mol TOTAL = 164.10 g/mol 1 mol of Ca(NO 3 ) 2 masses 164.10 g.

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Molar Mass of Compounds How many moles of CO 2 are in 22.0 grams of CO 2 ? MM of CO 2 = 1 x 12.01 g/mol = 12.01 g/mol 2 x 16.00 g/mol = 32.00 g/mol TOTAL = 44.01 g/mol 22.0 g CO 2 g CO 2 mol CO 2 1 44.01 = 0.500 mol CO 2

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Molar Mass of Compounds What is the mass (in grams) of 10.5 moles of SO 2 ? MM of SO 2 = 1 x 32.07 g/mol = 32.07 g/mol 2 x 16.00 g/mol = 32.00 g/mol TOTAL = 64.07 g/mol 10.5 mol SO 2 mol SO 2 g SO 2 64.07 1 = 673 g SO 2

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Molar Mass of Hydrates Hydrate – an ionic cmpd that has water molecules in it. EXAMPLES: CuSO 4 5H 2 O Fe(NO 3 ) 3 9H 2 O Ba(C 2 H 3 O 2 ) 2 2H 2 O

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Molar Mass of Hydrates The MM of CuSO 4 5H 2 O is: 1 x Cu = 1 x 63.55 g/mol = 63.55 g/mol 1 x S = 1 x 32.07 g/mol = 32.07 g/mol 4 x O = 4 x 16.00 g/mol = 64.00 g/mol 5 x H 2 O = 5 x 18.02 g/mol = 90.10 g/mol TOTAL = 249.72 g/mol 1 mol of CuSO 4 5H 2 O masses 249.72 g.

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