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IIIIIIIV Topic 6 The Mole I. Molar Conversions

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A. What is the Mole? n A counting number (like a dozen) n Avogadro’s number (N A ) n 1 mol = 6.02 10 23 representative particles (atoms, ions, formula units, or molecules If you could spend 1 million dollars per second, how many years will it take to spend a mole of dollars, given there are 31536000 seconds per year. 1.91 x 10 10 years or 19.1 billion years

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n 1 mole of hockey pucks would equal the mass of the moon! A. What is the Mole? n 1 mole of pennies would cover the Earth 1/4 mile deep! n 1 mole of basketballs would fill a bag the size of the earth!

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A. Moles n Used as a Conversion Factor: n 1 mole = 6.02 x 10 23 so… n Moles converted to Particles = # mol 6.02 10 23 Particles 1 mol

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A. Moles n Rep. Particles converted to moles = # particles 1 mol 6.02 10 23 Particles

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B. Molar Mass n Mass of 1 mole of an element or compound. n Atomic mass tells the... atomic mass units per atom (amu) grams per mole (g/mol) n Round to 2 decimal places

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B. Molar Mass Examples n carbon n aluminum n zinc 12.01 g/mol 26.98 g/mol 65.39 g/mol

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B. Molar Mass Examples n water n sodium chloride H2OH2O (2x1.01) + 16.00 = 18.02 g/mol NaCl 22.99 + 35.45 = 58.44 g/mol

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B. Molar Mass Examples n sodium hydrogen carbonate n sucrose NaHCO 3 22.99 + 1.01 + 12.01 + (3x16.00) = 84.01 g/mol C 12 H 22 O 11 (12x12.01) + (22x1.01) + (11x16.00) = 342.34 g/mol

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C. Molar Conversions molar mass (g/mol) MASS IN GRAMS MOLES NUMBER OF PARTICLES 6.02 10 23 (particles/mol)

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C. Molar Conversion Examples n How many molecules are in 2.50 moles of C 12 H 22 O 11 ? 2.50 mol 6.02 10 23 molecules 1 mol = 1.51 10 24 molecules C 12 H 22 O 11

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C. Molar Conversion Examples n How many moles of carbon are in 26 g of carbon? 26 g C 1 mol C 12.01 g C = 2.2 mol C

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C. Molar Conversion Examples n Find the mass of 2.1 10 24 molecules of NaHCO 3. 2.1 10 24 molecules 1 mol 6.02 10 23 molecules = 290 g NaHCO 3 84.01 g 1 mol

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IIIIIIIV II. Formula Calculations Topic 6 – The Mole

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A. Percentage Composition n the percentage by mass of each element in a compound

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100 = A. Percentage Composition %Cu = 127.10 g Cu 159.17 g Cu 2 S 100 = %S = 32.07 g S 159.17 g Cu 2 S 79.852% Cu 20.15% S n Find the % composition of Cu 2 S.

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%Fe = 28 g 36 g 100 = 78% Fe %O = 8.0 g 36 g 100 = 22% O n Find the percentage composition of a sample that is 28 g Fe and 8.0 g O. A. Percentage Composition

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n How many grams of copper are in a 38.0-gram sample of Cu 2 S? (38.0 g Cu 2 S)(0.79852) = 30.3 g Cu Cu 2 S is 79.852% Cu A. Percentage Composition

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100 = %H 2 O = 36.04 g 147.02 g 24.51% H 2 O n Find the mass percentage of water in calcium chloride dihydrate, CaCl 2 2H 2 O? A. Percentage Composition

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B. Empirical Formula C2H6C2H6 CH 3 reduce subscripts n Smallest whole number ratio of atoms in a compound

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B. Empirical Formula Calculation 1. Find mass (or %) of each element. 2. Find moles of each element. 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

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B. Empirical Formula n Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g 1 mol 14.01 g = 1.85 mol N 74.1 g 1 mol 16.00 g = 4.63 mol O 1.85 mol = 1 N = 2.5 O

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B. Empirical Formula N 1 O 2.5 Need to make the subscripts whole numbers multiply by 2 N2O5N2O5

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C. Molecular Formula n “True Formula” - the actual number of atoms in a compound CH 3 C2H6C2H6 empirical formula molecular formula ?

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C. Molecular Formula Calculation 1. Find the empirical formula. 2. Calculate the empirical formula molar mass. 3. Divide the molecular molar mass by the empirical molar mass. 4. Multiply each subscript by the answer from step 3.

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C. Molecular Formula n The empirical formula for ethylene is CH 2. Find the molecular formula if the molecular mass is 28.06 g/mol? 28.06 g/mol 14.03 g/mol = 2.00 empirical mass = 14.03 g/mol (CH 2 ) 2 C 2 H 4

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IIIIIIIV III. Molarity Topic 6 The Mole

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A. Molarity n Concentration of a solution. total combined volume substance being dissolved

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A. Molarity 2M HCl What does this mean?

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B. Molarity Calculations molar mass (g/mol) 6.02 10 23 (particles/mol) MASS IN GRAMS MOLES NUMBER OF PARTICLES LITERS OF SOLUTION Molarity (mol/L) Aqueous solution

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B. Molarity Calculations n How many grams of NaCl are required to make 0.500L of 0.25M NaCl? 0.500 L0.25 mol 1 L = 7.3 g NaCl 58.44 g 1 mol

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B. Molarity Calculations n Find the molarity of a 250 mL solution containing 10.0 g of NaF. 10.0 g 1 mol 41.99 g = 0.238 mol NaF 0.238 mol 0.25 L M == 0.95M NaF

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1 mol of any gas=22.4 L at STP C. Molar Volume at STP S tandard T emperature & P ressure 0°C and 1 atm

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C. Molar Volume at STP Molar Mass (g/mol) 6.02 10 23 particles/mol MASS IN GRAMS MOLES NUMBER OF PARTICLES LITERS OF SOLUTION Molar Volume (22.4 L/mol) LITERS OF GAS AT STP Molarity (mol/L)

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C. Molar Conversion Examples n How many Liters are in 2.50 moles of of Helium gas at STP? 2.50 mol 22.4 L 1 mol = 56.0 L He

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C. Molar Conversion Examples n Find the mass of 137 L of SO 2 gas at STP. 137 L SO 2 1 mol 22.4 L SO 2 = 392 g SO 2 64.07 g 1 mol

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