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AP Notes Chapter 7 Mole Representative Particles Molecular Mass (mm) - gam used for atoms - gmm used for molecules - gfm used for formula units MoleVolume Mixed Mole Conversions

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The Mole A dozen is a counting number that means 12. A dozen is a counting number that means 12. The mole is a counting number. The mole is a counting number. A very large number, but still, just a number. A very large number, but still, just a number. 6.022 x 10 23 of anything is a mole or mol 6.022 x 10 23 of anything is a mole or mol Items that we count with the mole are called representative particles Items that we count with the mole are called representative particles They are: They are: atoms, ions, molecules and formula units

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Moles to representative particles How many atoms of carbon will it take to have 1.237moles of C? 1.237mol C x (6.02x10 23 atoms) = 1 mole 1 mole = 7.44674x10 23 = 7.44674x10 23 = 7.447x10 23 mol C

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Representative particles to moles How many mole are there in 4537.8 molecules of methane CH 4 ? 4537.8 CH 4 x 1mole = (6.02x10 23 molecules) (6.02x10 23 molecules) = 7.53787375x10 -21 = 7.5379x10 -21 moles CH 4

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Molar mass 12.0 grams of C-12 contains a mole of atoms. 12.0 grams of C-12 contains a mole of atoms. Makes the mass numbers on the periodic table the mass of the average atom. Makes the mass numbers on the periodic table the mass of the average atom. Mass of 1 mole of a substance. Mass of 1 mole of a substance. Often called molecular weight. Often called molecular weight.

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Molar mass To determine the molar mass of an element, (gam) look on the table. To determine the molar mass of an element, (gam) look on the table. To determine the molar mass of a molecular compound, (gmm) add up the molar masses of the elements that make it up. To determine the molar mass of a molecular compound, (gmm) add up the molar masses of the elements that make it up.

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Since this is an atom (gam) Find the molar mass of Li: Look up on the periodic table & find the mass of Li: 6.941grams/mole For convenience sake, we round to the tenths place for a mass of 6.9 grams/mol

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Since this is an molecule (gmm) Find the molar mass of O 2 : Look up on the periodic table & find the mass of O: 15.999 grams/mole For convenience sake, we round to the tenths place for a mass of 16.0 grams/mol Since there are two oxygen atoms in O 2 we must have the mass of two oxygens or 2 x 16.0g = 32.0 g

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Since this is an molecule (gmm) Find the molar mass of CH 4 : Look up on the periodic table & find the mass of C: 12.011 grams/mole => 12.0g/mol Look up on the periodic table & find the mass of H: 1.0079 grams/mole => 1.0g/mol Since there are four hydrogen atoms in CH 4 we must have the mass of four hydrogens; 4 x 1.0g = 32.0 g Add the masses 12.0g/mol + 32.0g/mol = 44.0 g/mol

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For ionic compounds use (gfm) Mg 3 P 2 Find the molar mass of Mg 3 P 2 : Look up on the periodic table & find the mass of Mg: 24.305 grams/mole => 24.3g/mol Look up on the periodic table & find the mass of P: 30.974 grams/mole => 31.0g/mol Since there are three magnesium atoms in, we must have the mass of 3 Mg; 3 x 24.3g = 72.9 g Since there are two phosphorus atoms in, we must have the mass of 2 P; 2 x 31.0g = 62.0g Add the masses 72.9g/mol + 62.0g/mol = 134.0 g/mol

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For ionic compounds use (gfm) Ca(NO 3 ) 3 Find the molar mass of Ca(NO 3 ) 3 : Look up on the periodic table & find the mass of Ca: 24.305 grams/mole => 24.3g/mol Look up on the periodic table & find the mass of NO 3 : 14.0g + 3 x (16.0g) = 48.0g/mol Since there are three nitrates we must have the mass of three nitrogen and nine oxygen atoms: 3 x (NO 3 ) or 3 x 48.0g = 144.0g/mol Add the masses 24.3g/mol + 144.0g/mol = 168.3 g/mol

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For ionic compounds use (gfm) Al 2 (Cr 2 O 7 ) 3 Find the molar mass of Al 2 (Cr 2 O 7 ) 3 : Look up & find the mass of : Aluminum, Chromium & Oxygen: 2 x Al = 2 x 27.0g = 54.0g 6 x Cr = 6 x 52.0g = 312.0g 21 x O = 21 x (16.0g) = 336.0g/mol Add all the masses: 54.0g/mol + 312.0g/mol + 336.0 g/mol = = 702.0g/mol

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For ionic compounds use (gfm) CaSO 4 · 2H 2 O Find the molar mass of CaSO 4 · 2H 2 O : Look up & find the mass of : Calcium, Sulfur, Oxygen: Ca = 40.1 and S = 32.1 = 72.2g 4 x O = 4 x (16.0g) = 64.0g Water for the Hydrated compound: H 2 O = (2 x 1.0g) + 16.0g = 18.0 g 2(H 2 O) = 2 x 18.0g = 36.0g 72.2g/mol + 64.0g/mol + 36.0 g/mol = 172.2g/mol

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Mole to mass conversions 24.3g of O 2 is how many moles of O 2 ? If you want to convert between moles and grams you need a molar mass Remember O 2 = 2 x 16.0g = 32.0 g 24.3g O 2 x 1mole O 2 = 0.759375 mole O 2 32.0g O 2 => 0.759 mole O 2

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Moles to mass conversion 1.758 moles of Ca(NO 3 ) 3 is how many grams? If you want to convert between moles and grams you need a molar mass Remember: 168.3 g/mol 1.758mol x 168.3g = 295.8714g => 295.9g 1mol

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Mole to volume conversion The volume of a mole of any gas at (STP) standard temperature and pressure is 22.4L or 1mol = 22.4L What volume would 3.4moles of CH 4 occupy? 3.4mol CH4 x 22.4L = 76.16L 1mol 1mol => 76L => 76L

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Volume to mole conversion 487.2L of CO 2 are produced by one car in a year. How many moles of CO 2 is that? 487.2L CO 2 x 1mole = 22.4L 22.4L = 21.75mol CO 2

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Using DA for multi step conversions How many grams are there in 100.0 Liters of Helium? We don’t know a mass to volume conversion. But, we do know that they can both be related to the mole. 100.0L He x 1mol x (4.0g He) = 22.4L 1mol 22.4L 1mol = 17.85714g = 17.85714g = 17.86g He = 17.86g He

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