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CHAPTER 7

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CHAPTER 7

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  1. CHAPTER 7 Chemical Calculations 7.1-7.7

  2. The Mole • A number of atoms, ions, or molecules that is large enough to see and handle. • A mole = number of things • Just like a dozen = 12 things • One mole = 6.022 x 1023 things • Avogadro’s number = 6.022 x 1023 • Symbol for Avogadro’s number is NA.

  3. The Mole

  4. The Mole • How do we know when we have a mole? • count it out • weigh it out • Molar mass - mass in grams numerically equal to the atomic weight of the element in grams. • H has an atomic weight of 1.00794 g • 1.00794 g of H atoms = 6.022 x 1023 H atoms • Mg has an atomic weight of 24.3050 g • 24.3050 g of Mg atoms = 6.022 x 1023 Mg atoms

  5. The Mole

  6. The Mole • Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures.

  7. The Mole • Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures.

  8. The Mole • Example 2-1: Calculate the mass of a single Mg atom in grams to 3 significant figures.

  9. The Mole • Example 2-1: Calculate the mass of a single Mg atom, in grams, to 3 significant figures.

  10. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  11. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  12. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  13. The Mole • Example 2-2: Calculate the number of atoms in one-millionth of a gram of Mg to 3 significant figures.

  14. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  15. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  16. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  17. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  18. The Mole • Example 2-3. How many atoms are contained in 1.67 moles of Mg?

  19. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? You do it!

  20. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg?

  21. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg?

  22. The Mole • Example 2-4: How many moles of Mg atoms are present in 73.4 g of Mg? IT IS IMPERATIVE THAT YOU KNOW HOW TO DO THESE PROBLEMS

  23. Formula Weights, Molecular Weights, and Moles • How do we calculate the molar mass of a compound? • add atomic weights of each atom • The molar mass of propane, C3H8, is:

  24. Formula Weights, Molecular Weights, and Moles • The molar mass of calcium nitrate, Ca(NO3)2 , is: You do it!

  25. Formula Weights, Molecular Weights, and Moles

  26. Formula Weights, Molecular Weights, and Moles • One Mole of Contains • Cl2 or 70.90g 6.022 x 1023 Cl2 molecules 2(6.022 x 1023 ) Cl atoms • C3H8You do it!

  27. Formula Weights, Molecular Weights, and Moles • One Mole of Contains • Cl2 or 70.90g 6.022 x 1023 Cl2 molecules 2(6.022 x 1023 ) Cl atoms • C3H8 or44.11 g 6.022 x 1023 C3H8 molecules 3 (6.022 x 1023 ) C atoms 8 (6.022 x 1023 ) H atoms

  28. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  29. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  30. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  31. Formula Weights, Molecular Weights, and Moles • Example 2-5: Calculate the number of C3H8 molecules in 74.6 g of propane.

  32. Formula Weights, Molecular Weights, and Moles • Example 2-8. Calculate the number of O atoms in 26.5 g of Li2CO3. You do it!

  33. Formula Weights, Molecular Weights, and Moles • Example 2-8. Calculate the number of O atoms in 26.5 g of Li2CO3.

  34. Percent Composition • % composition = mass of an individual element in a compound divided by the total mass of the compound x 100% • Determine the percent composition of C in C3H8.

  35. Percent Composition and Formulas of Compounds • What is the percent composition of H in C3H8? You do it!

  36. Percent Composition • What is the percent composition of H in C3H8?

  37. Percent Composition • Example 2-10: Calculate the percent composition of Fe2(SO4)3 to 3 significant figures. You do it!

  38. Percent Composition • Example 2-10: Calculate the percent composition of Fe2(SO4)3 to 3 sig. fig.

  39. Percent Composition

  40. Empirical and Molecular Formulas • Empirical Formula - smallest whole-number ratio of atoms present in a compound • Molecular Formula - actual numbers of atoms of each element present in a molecule of the compound • We determine the empirical and molecular formulas of a compound from the percent composition of the compound.

  41. Empirical And Molecular Formulas

  42. Empirical Formulas • Example 2-11: A compound contains 24.74% K, 34.76% Mn, and 40.50% O by mass. What is its empirical formula? • Make the simplifying assumption that we have 100.0 g of compound. • In 100.0 g of compound there are: • 24.74 g of K • 34.76 g of Mn • 40.50 g of O

  43. Empirical Formulas

  44. Empirical Formulas

  45. Empirical Formulas

  46. Empirical Formulas

  47. Empirical Formulas

  48. Empirical Formulas • Example 2-12: A sample of a compound contains 6.541g of Co and 2.368g of O. What is empirical formula for this compound? You do it!

  49. Empirical Formulas • Example 2-12: A sample of a compound contains 6.541g of Co and 2.368g of O. What is empirical formula for this compound?

  50. Empirical Formulas • Example 2-12: A sample of a compound contains 6.541g of Co and 2.368g of O. What is empirical formula for this compound?