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The Mole & Chemical Composition

The Mole & Chemical Composition. Section 1 Avogadro’s Number & Molar Conversions. For Review. Mole SI unit for amount # of atoms in 12g of carbon-12 Avogadro’s Number # of particles in a mole 6.022 x 10 23 - # of (?) in 1.000 mole Used to count any kind of particle.

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The Mole & Chemical Composition

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  1. The Mole &Chemical Composition Section 1 Avogadro’s Number & Molar Conversions

  2. For Review • Mole • SI unit for amount • # of atoms in 12g of carbon-12 • Avogadro’s Number • # of particles in a mole • 6.022 x 1023 - # of (?) in 1.000 mole • Used to count any kind of particle

  3. The Mole is a Counting Unit • Ex. – 1 dozen = 12 • The mole is used to count out a given number of particles, whether they are atoms, molecules, formula units, ions, or electrons.

  4. Amount in Moles converted to # of Particles • 6.022 x 1023 particles = 1 mol Choose a conversion factor that cancels the given units.

  5. Example #1 • Find the number of molecules in 2.5 mol of sulfur dioxide.

  6. Homework Practice A p. 228 #’s 2 - 4

  7. Example #2 • A sample contains 3.01 x 1023 molecules of sulfur dioxide, SO2. Determine the amount in moles.

  8. Homework Practice B p. 229 #’s 2 – 4 #5 c – g

  9. Molar Mass Relates Moles to Grams • The mass in grams of 1 mole of substance • = atomic mass of monatomic elements & formula mass of compounds & diatomic elements • Examples • Carbon = 12g/mol • O2 = 16+16 = 32g/mol • CH4 = 12+1+1+1+1 = 16g/mol

  10. Example #3 • Find the mass in grams of 2.44 x 1024 atoms of carbon, whose molar mass is 12.01 g/mol.

  11. Homework • Practice C p. 231 #’s 2-4

  12. Example #4 • Find the number of molecules present in 47.5 g of glycerol, C3H8O3. The molar mass of glycerol is 92.11g/mol.

  13. Homework • Practice D p. 232 #’s 2, 3

  14. Quiz.7.1 Answer List • 57.41 g • 695 g • 1.4 x 1024 atm • 1.195 mol • 0.0206 mol

  15. The Mole &Chemical Composition Section 2 Relative Atomic Mass & Chemical Formulas

  16. For Review • Isotope – atoms of the same element with different #’s of neutrons (different mass #’s) • Average Atomic Mass – weighted average of atomic masses of elements isotopes

  17. Calculating Average Atomic Mass • Need to know % abundance to calculate avg. atomic mass • Native copper is a mixture of two isotopes. Copper-63 contributes 69.17% of the atoms, and copper-65 the remaining 30.83%.

  18. Example #1 • The mass of Cu-63 atom is 62.94 amu, and that of a Cu-65 atom is 64.93 amu. Using the data for the previous figure, find the average atomic mass of Cu.

  19. Practice #1 • Calculate the average atomic mass for gallium if 60.00% of its atoms have a mass of 68.926 amu and 40.00 % have a mass of 70.925 amu. • Calculate the average atomic mass of oxygen. Its composition is 99.76% of atoms with a mass of 15.99 amu, 0.038% with a mass of 17.00 amu, and 0.20% with a mass 18.00 amu.

  20. To Understand • Chemical formula • Which elements • How much of each • Ionic compounds • Show simplest ratio of cations & anions • KBr – 1:1 – 1 K+ & 1 Br-

  21. Molar Mass of Compound • = sum of masses of all atoms in g/mol • Ex. H2O - H → 2 x 1.00 = 2.00 - O → 1 x 16.00 = 16.00 18.00 g/mol

  22. Examples • ZnCl2 • (NH4)2SO4

  23. Practice – Homework Practice F p. 239 - 240 #’s 1 - 4

  24. The Mole &Chemical Composition Section 3 Formulas & Percent Composition

  25. Definitions • Percent composition – percentage by mass of each element in a compound • Empirical formula – shows simplest ratio • a chemical formula that shows the composition of a compound in terms of relative #’s & kinds of atoms

  26. Example – Find the empirical formula. C – 60.0% H – 13.4% O – 26.6% 1. Convert mass to moles. Assume you have a 100g sample.

  27. Example – Find the empirical formula. 2. formulas are written using whole #’s (to convert divide by smallest) 3. Write formula C3H8O

  28. Practice – In Class • A compound is 63.52% Fe and 36.48% S. • 26.58% K, 35.35% Cr, 38.07% O • 32.37% Na, 22.58% S, 45.05% O

  29. Practice – Homework Practice G p. 243 #’s 1 - 4

  30. Definitions • Molecular formulas – whole # multiple of empirical formula • Ex. EmpiricalMolecular – CH2O x 1 = CH2O formaldehyde x 2 = C2H4O2 acetic acid x 6 = C6H12O6 glucose

  31. Example- Find the molecular formula. • The empirical formula for a compound is P2O5. Its experimental molar mass is 284 g/mol. Determine the molecular formula of the compound.

  32. Practice – In ClassWhat is the molecular formula? • Experimental MM = 232.41 g/mol Empirical formula = OCNCl • Experimental MM = 32.06 g/mol Empirical formula = NH2

  33. Practice - Homework Practice H p. 245 #’s 1 - 3

  34. Percent Composition • Calculate the percent composition of copper (I) sulfide, a copper ore called chalcocite. Check that everything adds up to 100%

  35. Practice – In Class Determine the % Composition • NaClO • H2SO3 • C2H5COOH

  36. Answers to Practice

  37. Answers to Practice

  38. Answers to Practice

  39. Qz.7.3Calculate the percent composition • SrBr2 • CaSO4 • Mg(CN)2 • Pb(CH3COO)2

  40. Practice - Homework Practice I p. 248 #’s 1- 4

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