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# CH 6 - Chem 100 Chapter 6 Counting Atoms by the Gram Can...

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Anna Toy-Palmer 1 Chem 100 Chapter 6 -- Counting Atoms by the Gram Can determine mass or weight of a group of objects by counting the number of objects Nails (0.150 lb nails = 1 dozen nails) Buying 120 nails is buying 1.5 lbs Sometimes for integral objects, easier to count number of objects to get “weight” or mass than weighing objects Instead of weighing atoms to determine mass, count them

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Anna Toy-Palmer 2 Chem 100 Converting between mass and number of atoms For atoms, we need a number that we can easily convert between number of atoms and a tangible mass. Avogadro’s number 1 mole (1 mol) = 6.022 X 10 23
Anna Toy-Palmer 3 Chem 100 Avogadro’s number 1 mol ANYTHING = 6.022 X 10 23 ANYTHING Numerical value of a mole is defined as being equal to the number of atoms in exactly 12 g of pure carbon-12 1 mol carbon atoms (pure carbon-12) = 6.022 X 10 23 carbon atoms = 12 g of pure carbon-12

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Anna Toy-Palmer 4 Chem 100 How many guacs are in a bowl of guacamole? Avocados number. If a mole of moles were digging a mole of holes, what would you see? A mole of molasses. What did Avogadro contract when he was bitten by 6.022 X 10 23 mosquitoes? Mole-aria What was Avogadro’s favorite subject in school? Mole- tiplication How did Avogadro exaggerate? He made mountains out of mole hills.
Anna Toy-Palmer 5 Chem 100 Moles to number of atoms (conversion factor) 1 mol atoms = 6.022 X 10 23 atoms 3.5 mol of He atoms. How many He atoms do we have? 3.5 moles X 6.022 X 10 23 atoms/mole = 2.1 X 10 24 atoms

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Anna Toy-Palmer 6 Chem 100 Molar mass (grams and moles of an element) Molar mass is the mass of 1 mol of atoms. This value is equal to the elements atomic mass in atomic mass units. What is the mass of 1 mole of hydrogen atoms? What is the mass of 1 mol of oxygen atoms? What is the mass of 1 mol of helium atoms?
Anna Toy-Palmer 7 Chem 100 Converting between moles and grams We are given 3.2 mol of C. How many grams do we have? From the periodic table, 12.011g of C = 1 mol of C 3.2 mol C 12.011 g C 1 mol C = 38 g C

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Anna Toy-Palmer 8 Chem 100 We are given 13.5 g of mercury. How many mols of mercury do we have? From the periodic table: 1 mol Hg = 200.59 g Hg 13.5 g Hg 1 mol Hg 200.59 g Hg = 6.73 X 10 -2 mol Hg
Anna Toy-Palmer 9 Chem 100 Converting between grams and atoms We are given 12.7 g of Fe. How many atoms of Fe do we have? From the periodic table, 55.845 g Fe = 1 mol Fe Avogadro’s number: 1 mol Fe = 6.022 X 10 23 atoms Fe 12.7 g Fe 1 mol Fe 55.845 g Fe = 1.37 X 10 23 atoms Fe 1 mol Fe 6.022 X 10 23 atoms Fe

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Anna Toy-Palmer 10 Chem 100 Given 22.5 g of helium, how many moles of helium do we have? How many atoms of helium do we have?
Anna Toy-Palmer 11 Chem 100 Given 22.5 g of helium, how many moles of helium do we have? How many atoms of helium do we have? Atomic mass of He: 4.0026 g/mol 22.5 g He 1 mol He = 5.62 mol He 4.0026 g He 22.5 g He 1 mol He 6.022 X 10 23 atoms He = 4.0026 g He 1 mol He 3.39 X 10 24 atoms of He

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Anna Toy-Palmer 12 Chem 100 Molecules by the gram Formula Mass = sum of the atomic mass of the elements that the compound is composed of Water = H 2 O 2 hydrogens, 1 oxygen Formula mass of water = 2 X (1.00794 amu) + 1 X (15.9994 amu) Formula mass of water = 18.0153 amu Molar mass of water = 18.0153 g/mol
Anna Toy-Palmer 13 Chem 100 What is the formula weight and molar mass of chromium (III) oxide?

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CH 6 - Chem 100 Chapter 6 Counting Atoms by the Gram Can...

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