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Chapter 11 Mathematics & Chemical Formulas Unit 6 – The Mole

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Atoms are too small/light Atoms are too small and too light to count or mass as individuals – One Carbon-12 atom = 1.99 x 10 -23 grams We use this as the basis for atomic mass units. 1 Carbon atom is 12 amu. – 6 protons + 6 neutrons = 12 “things” that make up the mass of a carbon atom One amu = 1/12 of a carbon atom

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Atomic Mass & Formula Mass Atomic mass - the mass of 1 mole of atoms (also known as “molar mass”) Formula mass - the masses of all the atoms in an ionic compound. Ex: CaCl 2 Molecular Mass – the masses of all of the atoms in a molecular compound. Ex: CH 4

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Formula Weight (FW) So, the formula weight of calcium chloride, CaCl 2, would be Ca: 1(40.1 amu) + Cl: 2(35.5 amu) 111.1 amu To convert to molar mass, change amus to g/mol. 1 amu = 1 g/mol

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Molecular Weight (MW) For the molecule methane, CH 4, the molecular weight would be C: 1(12.0 amu) 16.0 amu + H: 4(1.0 amu) The molar mass of methane would be 16.0 g/mol

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1 mole - different physical states Moles provide a bridge from the molecular scale to the real-world scale.

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Examples of Molar Mass List the molar masses of the following: – Zn – CuSO 4 – NaCl – H 2 O – Al 2 (SO 4 ) 3

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The Mole – a word that means a # Other words that mean #s: One dozen = 12 One gross = 144 One score = 20 One ream = 500 One MOLE = 6.02 x 10 23 602000000000000000000000

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Where does Avogadro’s Number come from? A formula: M = N A m C The mass of 1 carbon-12 atom is 1.99 x 10 -23 g

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Avogadro’s Number Avogadro’s Number - 6.02 x 10 23 particles in 1 mole 1 mole of 12 C has a mass of 12 g.

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Mole Conversions Moles tell you how many atoms you have, AND how much mass in grams you have. We use moles to convert from atoms and grams.

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Mole Conversion Factors There are 4 possible conversion factors for mole conversions: – Show your work -use a conversion factor every time

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Mole Diagram – Conversion Factors

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Using your calculator To Enter 6.02 x 10 23 into your calculator, use the EE button, so it would appear as 6.02E23. Practice with the two following examples

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Examples: If you have 4.25 x 10 22 atoms of Al, how many moles do you have? If you have 0.37 moles of Al, how many atoms do you have?

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Mole Examples (lol) If you have 8.64g of Mg, how many moles do you have? If you have 1.23 moles of Phosphorous, how many grams do you have?

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Mole Relationships One mole of: – atoms – ions – molecules contains Avogadro’s number of those particles. One mole of: – molecules or formula units contains Avogadro’s number times the number of atoms or ions of each element in the compound.

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