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Chapter 2

# Chapter 2 - Formulas Equations and Yields Making Sense of...

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Formulas, Equations and Yields Making Sense of Chemical Processes

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Counting Molecules The mass of one atom is extremely small (e.g. a sodium atom has a mass of 3.80 x 10-23g) In the laboratory we perform chemical reactions that involve measureable masses of atoms The link between these two scales is Avogadro’s Number (NA) . Avogadro’s Number is the number of atoms in exactly 12g of 12C. NA = 6.0221420 x 1023 So, in other words in 12g of 12C there are 6.0221420 x 1023 atoms of 12C The mass (in grams) of NA atoms of any element is its atomic mass
The Mole 1 mole (mol) represents NA = 6.0221420 x 1023 atoms, molecules The mass of 1 mol of atoms of an element, or molecules of a compound, is the molar mass (g/mol) For elements the molar mass is equivalent to the atomic mass of the same element

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Example(s) How many moles of iron (Fe) are in 8.232g? # moles of iron = number of grams of iron / molar mass of iron = 8.232 g Fe / 55.847 g mol-1 = 0.1474 mol Fe How many Fe atoms in 8.232g? # atoms = # moles of iron x NA = 0.1474 mol x 6.0221420 x 1023 atoms / mol
Mass Moles Molar Mass Avogadro’s Number (NA)

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The “Size” Equivalent of One Mole Depends on the Species in Question
Density = Mass / Volume For one mole of a substance, Vm (Molar Volume) = Mass of one mole / Density of substance For one mole of water, Vm = 18.0g mol-1 / 1.0gcm-3 = 18 cm3 mol-1

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Chapter 2 - Formulas Equations and Yields Making Sense of...

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