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Chapter 6

Chapter 6. Chemical Composition. Counting by Weighing. Counting is time consuming Weighing is fast If we know average mass, we can count by weighing. Counting by Weighing. Plain M&Ms. Counting by Weighing. Peanut M&Ms. Atom are small. Really small. Gold.

stephen-david
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Chapter 6

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  1. Chapter 6 Chemical Composition

  2. Counting by Weighing • Counting is time consuming • Weighing is fast • If we know average mass, we can count by weighing

  3. Counting by Weighing • Plain M&Ms

  4. Counting by Weighing • Peanut M&Ms

  5. Atom are small • Really small Gold Atomic Force Microscope (AFM) that can simultaneously map surface topography and measure the "dragging" or frictional force of the tip as it scans across a surface.

  6. Atomic Masses: Counting by Weighing • Atomic Mass Units  amu • Only used for atoms • Very Small!! 1 amu = 1.66 x 10-24 g • Mass number units on periodic table: amu 1 atom

  7. Atomic Masses: Counting by Weighing • We need a reasonable number to weigh atoms • Avogadro (1776-1856) • Avogadro's Hypothesis: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. • He also proposed that oxygen gas and hydrogen gas were diatomic molecules.

  8. The Mole Avogadro’s Number 6.022 x 10 23 602200000000000000000000

  9. Mole Facts • 6.02 X 1023  Watermelon Seeds: Would be found inside a melon slightly larger than the moon. • 6.02 X 1023  Donut Holes: Would cover the earth and be 5 miles (8 km) deep. • 6.02 X 1023  Pennies: Would make at least 7 stacks that would reach the moon.

  10. Mole Facts • 6.02 X 1023  Grains of Sand: Would be more than all of the sand on Miami Beach. • 6.02 X 1023  Blood Cells: Would be more than the total number of blood cells found in every human on earth. • 6.02 X 1023  C02 Molecules: Would be found in 1 Mole Balloon TM at STP. • 1 Liter bottle of Water contains 55.5 moles H20

  11. Mole Facts • 5 Pound Bag of Sugar contains 6.6 moles of C12H22O11 • 1 Mole BalloonTM: Contains 22.4 Liters of any gas at STP. • There are 3 types of moles that live underground in North America: Eastern Mole, Hairy-Tailed Mole and Star-Nosed Mole • The "Mexican" Mole: Is a chocolate sauce or turkey stew. It comes from the Aztec word "molli." For recipes go to Web Hangouts.

  12. grams  moles  molecules

  13. Molar Mass • A chemical compound is a collection of atoms • Molar mass is the mass in grams of one mole of a chemical compound • To find molar mass, add up the masses of all the atoms

  14. Figure 6.3: Various numbers of methane molecules.

  15. Molar Mass ofSulfur dioxide • Sulfur dioxide = SO2 • 1 mole SO2  1 mole S atoms  2 moles O atoms • 1 mole S atoms = 1 X 32.07 g = 32.07 g 2 moles O atoms = 2 X 16.00 g = 32.00 g 1 mole SO2molecules = 64.07 g/mol • Don’t round molar mass

  16. Molar Mass of PVC • PVC is polyvinyl chloride, C2H3Cl • What is the mass of 1 mole C2H3Cl? • 2 mol C atoms = 2 x 12.01 = 24.02 g 3 mol H atoms = 3 x 1.008 = 3.024 g 1 mol Cl atoms = 1 x 35.45 = 35.45 g = 62.494 g/mol • Don’t round molar mass

  17. Sodium nitride, Na3N Carbon disulfide , CS2 Ammonium bromide, NH4Br Ethyl alcohol, C2H5OH 82.98 g/mol Na3N 76.15 g/mol CS2 97.942 g/mol NH4Br 46.068 g/mol C2H5OH Calculate Molar Mass

  18. Calculating Mass from Moles • What is the mass of 4.86 mol of CaCO3? • Molar Mass of CaCO3? • 1 mol Ca = 1 x 40.08 g = 40.08 g 1 mol C = 1 x 12.01 g = 12.01 g 3 mol O = 3 x 16.00 g = 48.00 g Molar mass of CaCO3 = 100.09 g/mol

  19. Calculating Mass from Moles • Molar mass of CaCO3 = 100.09 g • What is the mass of 4.86 mol of CaCO3? • 4.86 mol CaCO3 x 100.09 g = ? mol = 486 g CaCO3

  20. Moles from Mass • How many moles is 1.56 g of juglone? • Juglone is a dye used for centuries that produced from black walnut trees. It is also a natural herbicide. • Formula = C10H6O3 • Find Molar Mass of juglone • 174.1 g/mole

  21. Moles from Mass • 1mol = 174.1 g of juglone • 1.56 g juglone x 1 mol juglone =? 174.1 g • 0.00896 mol juglone • 8.96 x 10-3 mol juglone

  22. Percent Composition of Compounds • Percent by mass Percent = x 100% Mass fraction of a given = element Part Whole Mass of element present in 1 mol of compound Mass of 1 mol of compound

  23. Percent by Mass of Each Element in PVC, C2H3Cl 2 mol C atoms = 2 x 12.01 = 24.02 g 3 mol H atoms = 3 x 1.008 = 3.024 g 1 mol Cl atoms = 1 x 35.45 = 35.45 g = 62.494 g/mol % C = x 100% = 38.44 % C % H = x 100% = 4.84 % H % Cl = x 100% = 56.73 % Cl 24.02 g 62.494g 3.024 g 62.494g 35.45 g 62.494g 100.01 % Total to check

  24. grams  moles  molecules

  25. Percent by Mass

  26. Mole Day, March 20, 2008 • Celebrated annually on October 23 from 6:02 a.m. to 6:02 p.m., Mole Day commemorates Avogadro's Number (6.02 x 1023), which is a basic measuring unit in chemistry. For second term, we are celebrating on March 20th. • Mole Day was created as a way to foster interest in chemistry. Schools throughout the United States and around the world celebrate Mole Day with various activities related to chemistry and/or moles.

  27. Mole Day, March 20, 2008 • For a given molecule, one mole is a mass (in grams) whose number is equal to the atomic mass of the molecule. For example, the water molecule has an atomic mass of 18, therefore one mole of water weighs 18 grams. An atom of neon has an atomic mass of 20, therefore one mole of neon weighs 20 grams. • In general, one mole of any substance contains Avogadro's Number of molecules or atoms of that substance. This relationship was first discovered by Amedeo Avogadro (1776-1858) and he received credit for this after his death.

  28. Extra Credit Mole Day Projects • Make Mole Day treats to share: • Moleasses cookies, Avogadro Dip, Mole Cake, Guacamole or Taco-mole sauce • Make an object of “mole” art • Create a “Moletin” Board or poster • Write a Mole Day poem or song to perform for the class • Create a “Mole-opoly” game • Create mole day flag or costume • Create a mole day T-shirt (5-points maximum) • Make a mole piñata or a stuffed mole

  29. Extra Credit Mole Day Projects • 0 to 20 points extra credit are possible. Points given will be based on effort and creativity and added to your homework grade. • You may do more than one project BUT you may receive a maximum of 20 points. • There is no make-up or late projects allowed.

  30. grams  moles  molecules

  31. Figure 6.5: Ball-and-stick model of P4O10.

  32. Empirical Formula of a Compound • Converting masses measured in laboratory to chemical formulas • Need to convert gram to moles and then develop an empirical formula • Empirical Formula – the formula of a compound that expresses the smallest whole-number ratio of the atoms present. • Molecular Formula – the actual formula of the compound.

  33. Determining the Empirical Formula of a Compound (p. 179) • Step 1 - Obtain the mass of each element • Consider 100.0 g of the compound. • 33.88% Cu = 33.88 g Cu • 14.94% N = 14.94 g N • 51.18% O = 51.18 g O

  34. Determining the Empirical Formula of a Compound (p. 179) • Step 2 - Determine the number of moles of each element • 33.88 g Cu x = 0.5331 mol Cu • 14.94 g N x = 1.066 mol N • 51.18 g O x = 3.199 mol O 1 mole 63.55 g 1 mole 14.01 g 1 mole 16.00 g

  35. Determining the Empirical Formula of a Compound (p. 179) • Step 3 - Divide the number of moles of each element by the smallest number of moles to convert the smallest number to

  36. Determining the Empirical Formula of a Compound (p. 179) Step 3 continued - If all the number are integers (whole numbers), they are the subscripts in the empirical formula. If one or more of these numbers are not integers, go to Step 4. The empirical formula is CuN2O6 [i.e., Cu(NO3)2]

  37. Determining the Empirical Formula of a Compound (p. 179) • Step 4 – Multiply the numbers you derived in step 3 by the smallest number that will convert all of them to whole numbers. This set of numbers represents the subscripts in the empirical formula.

  38. Empirical Formula of a Compound • C6H12O6 = CH2O • C6H6 = CH • Na2O2 = NaO

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