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Chapter 7

Chapter 7. Chemical Quantities. Representative Particles. The smallest pieces of a substance. For a molecular compound it is a molecule . For an ionic compound it is a formula unit (a set of ions). For an element it is an atom . Counting Ions. How many ions in the following?

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Chapter 7

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  1. Chapter 7 Chemical Quantities

  2. Representative Particles • The smallest pieces of a substance. • For a molecular compound it is a molecule. • For an ionic compound it is a formula unit (a set of ions). • For an element it is an atom.

  3. Counting Ions How many ions in the following? 1) CaCl2 3 ions: 1 Ca and 2 Cl 2) NaOH 2 ions: 1 Na and 1 OH 3) Al2(SO4)3 5 ions: 2 Al and 3 SO4

  4. Counting Atoms How many oxygen atoms are in the following? 1) CaCO3 3 oxygen atoms 2) Al2(SO4)3 12 oxygen atoms

  5. Moles • Defined as the number of carbon atoms in exactly 12 grams of carbon-12. • 1 mole is 6.02 x 1023 particles. • Treat it like a very large dozen • 6.02 x 1023 is called Avogadro’s number.

  6. Gram Atomic Mass • The mass of 1 mole of an element in grams. • 12.01 grams of carbon has the same number of pieces as 1.01 grams of hydrogen and 55.85 grams of iron. • 12.01 g C = 1 mole C • Allows us to count things by weighing them. • Atomic Masses found on Periodic Table

  7. Gram Formula Mass • The mass of one mole of an ionic compound. • What is the GFM of Fe2O3? • 2 atoms Fe x 55.85 g = 111.70 g • 3 atoms O x 16.00 g = 48.00 g • GFM = 111.70 g + 48.00 g = 159.70g

  8. Gram Molecular Mass • Finding the mass of a molecular compound. • Calculated the same as GFM. • What is the mass of one mole of CH4? • 1 mole of C = 12.01 g • 4 mole of H x 1.01 g = 4.04g • 1 mole CH4 = 12.01 + 4.04 = 16.05g • The Gram Molecular mass of CH4 is 16.05g

  9. Molar Mass • The generic term for the mass of one mole. • The same as gram molecular mass, gram formula mass, and gram atomic mass. • DO NOT WRITE MOLAR MASSES IN SCIENTIFIC NOTATION!

  10. Examples #1 and 2 Calculate the molar mass of the following. 1)Na2S Na = 2 x 22.99 = 45.98 S = 1x 32.06 = 32.06 Molar Mass = 78.04 grams 2)N2O4 C N = 2 x 14.01 = 28.02 O = 4 x 16.00 = 64.00 C = 1 x 12.01 = 12.01 Molar Mass = 104.03 grams

  11. Example #3 Ca(NO3)2 Ca = 1 x 40.08 = 40.08 N = 2 x 14.01 = 28.02 O = 6 x 16.00 = 96.00 Molar Mass = 164.10 grams

  12. Example #4 C6H12O6 C = 6 x 12.01 = 72.06 H = 12 x 1.01 = 12.12 O = 6 x 16.00 = 96.00 Molar Mass = 180.18 g

  13. Example #5 (NH4)3PO4 N = 3 x 14.01 = 42.03 H = 12 x 1.01 = 12.12 P = 1 x 30.97 = 30.97 O = 4 x 16.00 = 64.00 Molar Mass = 149.12 g

  14. Converting to Mass from Moles One Step Problems

  15. Molar Mass • The number of grams in 1 mole of atoms, ions, or molecules. • We can make conversion factors from these. • Use to change grams of a compound to moles of a compound.

  16. Example #1 • How many moles is 5.69 g of NaOH?

  17. Example #1 • How many moles is 5.69 g of NaOH?

  18. Example #1 • How many moles is 5.69 g of NaOH? • need to change grams to moles

  19. Example #1 • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH

  20. Example #1 • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g

  21. Example #1 • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g • 1 mole NaOH = 40.00 g

  22. Example #1 • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g • 1 mole NaOH = 40.00 g

  23. Example #1 • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g • 1 mole NaOH = 40.00 g

  24. Example #2 How many grams is 9.87 moles of H2O? 9.87 mol H2O x 18.02 g H2O 1 mol H2O = 1.78 x 102 g H2O

  25. Example #3 How many moles of magnesium in 24.31 g of Mg? 24.31 g Mg x 1 mol Mg 24.31 g Mg = 1 mol Mg

  26. Example #4 How much would 2.34 moles of carbon weigh (in g)? 2.34 mol C x 12.01 g C 1 mol C = 2.81 x 101 g C

  27. Converting to Atoms & Molecules from Moles • One step problems • For elements: 1 mole = 6.02 x 1023 atoms • For molecular compounds: 1 mole = 6.02 x 1023 molecules • For ionic compounds: 1 mole = 6.02 x 1023 formula units

  28. Example #1 1) How many molecules of CO2 are there in 4.56 moles of CO2 ? 4.56 moles x 6.02 x 1023 molecules 1 mole = 2.75 x 1024 molecules CO2

  29. Example #2 How many moles of water is 5.87 x 1022 molecules? 5.87 x 1022 molecules x 1 mole 6.02 x 1023 molec = 9.75 x 10-2 moles water

  30. Example #3 How many moles is 7.78 x 1024 formula units of MgCl2? 7.78 x 1024 for. un. MgCl2 x 1 mole MgCl2 6.02 x 1023 for.un. MgCl2 = 1.29 x 101 mole MgCl2

  31. Watch out for this one! How many atoms of carbon are there in 1.23 moles of C6H12O6 ? 1.23 mol C6H12O6 x 6.02 x 1023 molec C6H12O6 x 6 atoms C 1 mol C6H12O61 molecC6H12O6 = 4.44 x 1024 atoms C

  32. 2 Step Problems • Converting from: • Mass to atoms • Molecules to mass • Mass to molecules • Atoms to mass • Formula units to mass • Mass to formula units

  33. Example #1 How many atoms of lithium in 1.00 g of Li? 1.00 g Li x 1 mol Li x 6.02 x 1023 atoms Li 6.94g Li 1 mol Li = 8.67 x 1022 atoms Li

  34. Example #2 How much would 3.45 x 1022 atoms of U weigh in grams? 3.45 x 1022 atoms U x 1 mol U x 238.03 g U 6.02 x 1023 atoms U 1 mol U = 1.36 x 101 g U

  35. Example #3 How many molecules in 6.8 g of CH4? 6.8 g CH4 x 1 mol CH4 x 6.02 x 1023 molec CH4 16.05 g CH4 1 mol CH4 = 2.55 x 1023 molec CH4

  36. Example #4 49 molecules of C6H12O6 weighs how many grams? 49 molecC6H12O6 x 1 mol C6H12O6 x 180.18 g C6H12O6 6.02 x 1023 molec C6H12O61 mol C6H12O6 = 1.47 x 10-20 g C6H12O6

  37. Gases and the Mole

  38. Gases • Many of the chemicals we deal with are gases. • They are difficult to weigh. • Need to know how many moles of gas we have. • Two things effect the volume of a gas Temperature and pressure • Compare at the same temp. and pressure.

  39. Standard Temperature and Pressure • 25ºC and 1 atm pressure • abbreviated STP • At STP 1 mole of gas occupies 22.4 L • Called the molar volume • Avogadro’s Hypothesis - at the same temperature and pressure equal volumes of gas have the same number of particles.

  40. Example #1 What is the volume of 4.59 mole of CO2 gas at STP? 4.59 mol CO2 x 22.4 L CO2 1 mol CO2 = 1.03 x 102 L CO2

  41. Example #2 How many moles is 5.67 L of O2 at STP? 5.67 L O2 x 1 mol O2 22.4 L O2 = 2.53 x 10-1 mol O2

  42. Example #3 What is the volume of 8.80g of CH4 gas at STP? 8.80 g CH4 x 1 mol CH4 x 22.4 L CH4 16.05 g CH4 1 mol CH4 = 1.23 x 101 L CH4

  43. Density of a Gas • D = m /V • for a gas the units will be g / L • We can determine the density of any gas at STP if we know its formula. • To find the density we need the mass and the volume. • If you assume you have 1 mole than the mass is the molar mass (PT) • At STP the volume is 22.4 L.

  44. Examples 1) Find the density of CO2 at STP. D = m/v D = 44.01 g /22.4 L D = 1.96 x 100 g/L 2) Find the density of CH4 at STP. D = m/v D = 16.05 g/22.4 L D = 7.17 x 10-1 g/L

  45. The other way • Given the density, we can find the molar mass of the gas. • Again, pretend you have a mole at STP, so V = 22.4 L. • m = D x V • m is the mass of 1 mole, since you have 22.4 L of the stuff.

  46. Examples 1)What is the molar mass of a gas with a density of 1.964 g/L? m = d x v m = 1.964 g/L x 22.4 L m = 4.40 x 101 g 2) What is the molar mass of a gas with a density of 2.86 g/L? m = d x v m = 2.86 g/L x 22.4 L m = 6.41 x 101 g

  47. We have learned how to change • change moles to grams • moles to atoms • moles to formula units • moles to molecules • moles to liters • molecules to atoms • formula units to atoms • formula units to ions

  48. Mass Moles

  49. Mass PT Moles

  50. Mass Volume PT Moles

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