# ch6 - Chapter 6 Tro Counting and weighing Example: Burning...

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Chapter 6 Tro Counting and weighing

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Example: Burning Aluminum Five hundred aluminum atoms were burned in oxygen. The resulting aluminum oxide had a total of 1250 atoms. What is the formula of aluminum oxide? Number of oxygen atoms = 1250 – 500 = 750 Ratio of oxygen atoms to aluminum atoms = 750/500 = 3/2. Therefore Al 2 O 3 .

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Burning Aluminum redux 26980. amu of aluminum is burned in oxygen to give 50980. amu of aluminum oxide. What is the formula of the oxide? Number of aluminum atoms = 26980. amu x (1 Al atom/26.98 amu) = 1000. Al atoms. Mass of oxygen = 50980 – 26980 = 24000 amu. Number of oxygen atoms = 24000 amu x (1 O atom/16.00 amu) = 1500. O atoms Ratio of oxygen atoms to aluminum atoms = 1500/1000 = 3/2 • Therefore formula is Al 2 O 3.
Counting Nails by the Pound I want to buy a certain number of nails for a project, but the hardware store sells nails by the pound! How do I know how many nails I am buying when I buy a pound of nails? Analogy How many atoms in a given mass of an element?

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Counting Nails by the Pound A hardware store customer buys 2.60 pounds of nails. A dozen of the nails has a mass of 0.150 pounds. How many nails did the customer buy? Solution map:
Counting Nails by the Pound The customer bought 2.60 lbs of nails and received 208 nails. He counted the nails by weighing them! nails 208 doz. 1 nails 12 lbs. 0.150 nails doz. 1 lbs. 2.60 = × ×

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Counting Nails by the Pound What if he bought a different size nail? Would the mass of a dozen be 0.150 lbs? Would there be 208 nails in 2.60 lbs? How would this effect the conversion factors?
Counting Atoms by Moles If we can find the mass of a particular number of atoms, we can use this information to convert the mass of a element sample to the number of atoms in the sample. The number of atoms we will use is 6.022 x 10 23 and we call this a mole 1 mole = 6.022 x 10 23 things Like 1 dozen = 12 things

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Chemical Packages - Moles mole = number of particles equal to the number of atoms in 12 g of C-12 1 atom of C-12 weighs exactly 12 amu 1 mole of C-12 weighs exactly 12 g The number of particles in 1 mole is called Avogadro’s Number = 6.0221421 x 10 23 1 mole of C atoms weighs 12.01 g and has 6.022 x 10 23 atoms the average mass of a C atom is 12.01 amu
Avogadro Number The conversion factor between amu and g is called the Avogadro number N o .

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## This note was uploaded on 04/11/2008 for the course CHE 101 taught by Professor Churchhill during the Fall '08 term at SUNY Buffalo.

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ch6 - Chapter 6 Tro Counting and weighing Example: Burning...

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