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Chapter 10 Worksheet Examples

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MOLAR MASS Worksheet:

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Example: Calculate the molar mass (gram molecular weight) of a mole of iodine, I 2. I = 126.9(2) = From the mass off of the periodic table. From the formula of the compound Unit for molar mass

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Example: Calculate the molar mass of a mole of aluminum sulfate (Al 2 (SO 4 ) 3 ). Al = (2) = S = (3) = O = (12) = add together = From the masses off of the periodic table. From the formula of the compound Unit for molar mass

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MOLE AS A UNIT OF MASS Worksheet:

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Example: What is the mass of 5.00 moles of water? 90.1 g H 2 O g / mol 5.00 mol Molar Mass Calculation H = 1.01 (2) = 2.02 O = (1) = = g / mol From the problem Molar mass X

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Example: What is the mass of 0.50 moles of calcium carbonate? g CaCO g / mol 0.50 mol Molar Mass Calculation Ca = (1) = C = (1) = O = (3) = = g / mol From the problem Molar mass X

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Example: How many moles of calcium chloride are in 333 grams of calcium chloride 333 g CaCl g / mol 3.00 mol Molar Mass Calculation Ca = (1) = Cl = (2) = = g / mol From the problem Molar mass ÷

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AVOGADRO’S NUMBER Worksheet:

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Example: How many molecules of water are there in 3.00 moles of water? 1.806x10 24 mcl H 2 O 6.02x10 23 mcl / mol 3.00 mol From the problem X The number of atoms/molecules in one mole is always 6.02x10 23

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Example: How many moles of neon are there in 2.408x10 24 atoms of neon? 2.408x10 24 atm Ne 6.02x10 23 atm / mol 3.99 mol From the problem The number of atoms/molecules in one mole is always 6.02x10 23 ÷

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MOLAR VOLUME OF A GAS Worksheet:

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Example: What is the volume, in liters, of a 2.00 mole sample of methane (CH 4 ) at STP? 44.8 L CH L / mol 2.00 mol From the problem The number of liters in one mole is always 22.4 X

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Example: How many moles of ethane (C 2 H 6 ) are there in 5.60 liters of ethane? 5.6 L C 2 H L / mol 0.25 mol From the problem The number of liters in one mole is always 22.4 ÷

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MIXED MOLE PROBLEMS Worksheet:

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We’ve done problems of one step. Moles to a unit or unit to moles. Now we can do multi step problems using this picture to help us see where we need to go next. This picture is a summary of all of the problems we have done up to this point along with helpful hints to units and numbers. The better you understand this the easier mole conversions will be. Molar mass is g/mol and you find grams from the periodic table.

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Example: What would be the volume in liters of grams of neon at STP? g Ne g / mol 2.00 mol ÷ 44.8 L Ne 22.4 L / mol 2.00 mol X We’re not to liters yet… From the problem From the periodic table The number of liters in one mole is always 22.4

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Example: How many molecules would there be in 56 liters of carbon dioxide at STP? 56 L CO L / mol 2.5 mol ÷ 1.505x10 24 mcl CO x10 23 mcl / mol 2.5 mol X We’re not to molecules yet… The number of liters in one mole is always 22.4 From the problem The number of atoms/molecules in one mole is always 6.02x10 23

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PERCENT COMPOSITION & FORMULAS Worksheet:

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Example: Calculate the percent composition of sodium hydrogen carbonate (NaHCO 3 )? Molar Mass Calculation Na = (1) = H = 1.01 (1) = 1.01 C = (1) = O = 16.00(3) = = g / mol Step 1 – find molar mass of the compound. Step 2 – divide mass of each element by molar mass. Step 3 – multiply answers by 100%.

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Example: Which pair of molecules has the same empirical formula? a)C 2 H 4 O 2 c) NaCrO 4 b)C 6 H 12 O 6 d) Na 2 Cr 2 O 7 CH 2 O An empirical formula is similar to a reduced fraction. Molecular formula Empirical formula These two can not be “reduced”.

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Example: Calculate the empirical formula for a compound with 67.6% Hg, 10.8% S, 21.6% O? Step 1 – change percents to grams (assume we have 100 gram sample then percents are the number of grams). Step 2 – change the grams to moles. Step 3 – divide all answers by the smallest number (of the answers). Step 4 – the results become the subscripts for the formula. ÷÷ Step 1 Step 2 Step 3 Step 4 HgSO 4

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Example: Find the molecular formula of ethylene glycol, which is used as antifreeze. The molecular mass is 62g/mol and the empirical formula is CH 3 O? Step 1 – Find the empirical formula mass (EFM) Step 2 – Divide the molar mass (from problem) by the EFM to get the multiplier. Step 3 – Use the multiplier to determine the subscripts by multiplying each subscript by the multiplier. Step 1 EFM Calculation C = (1) = H = 1.01 (3) = 3.03 O = 16.00(1) = =31.04 g / mol Step 2 MULTIPLIER Step 3 C 2 H 6 O 2

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