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HomeworkForPart2 8.4 The Mole Based on many experiments, chemists know the number of atoms in 1 gram atomic mass of an element is 6.02 x 10<sup>23</sup>. There are 6.02 x 10<sup>23</sup> hydrogen atoms in 1 gram atomic mass of hydrogen, 6.02 x 10<sup>23</sup> oxygen atoms in 1 gram atomic mass of oxygen and so on. The number 6.02 x 10<sup>23</sup> is called '''Avogradro's number''' and is known as 1 '''mole'''. Avogradro's number is represent by the letter N. Aluminum (Al): 1 mole, 1 gram atomic mass, 27 grams, 6.02 x 10<sup>23</sup> atoms Oxygen (O<sub>2</sub>): 1 mole, 1 gram atomic mass, 32 grams, 6.02 x 10<sup>23</sup> molecules Water (H<sub>2</sub>O): 1 mole, 1 gram atomic mass, 18 grams, 6.02 x 10<sup>23</sup> molecules Dry Ice (CO<sub>2</sub>): 1 mole, 1 gram atomic mass, 44 grams, 6.02 x 10<sup>23</sup> molecules When using the term "mole" in gaseous elements, it could refer to a mole of oxygen atoms or a mole of oxygen molecules. To avoid confusion, say "1 mole of oxygen atoms" or "1 mole of oxygen molecules." 8.5 Moles and Atoms 1 mole of atoms = 6.02 x 10<sup>23</sup> atoms Finding the mass in grams of 1 mole of atoms is just finding the gram atomic mass of the element Example: What is the mass of 5.0 moles of sulfur? the mass of 1 mol of sulfur is 32.1g. Therefore, the mass of 5.0 moles of sulfur must be 5 times the quantity. 5.0 moles S atoms x (32.1g S / 1.00 mol S atoms) = 160 g S (see pg 183 for more examples) 8.6 Moles and Formula Units 1 mole of molecular substance = 6.02 x 10<sup>23</sup> formula units Example: What is the mass of 1.0 mol of H<sub>2</sub>O? 1.0 mol of water means that there are 1.0 mol of water molecules. One mole of water molecules contains 2 moles of hydrogen atoms and 1 mole of oxygen atoms. H: 1g/mol x 2.0mol = 2g O: 16g/mol x 1 mol = 16g Mass of 1.0 mol of water molecules: 2g + 16g = '''18g''' 8.7 Mole Relationships 24 g C = 2.0 moles C = 1.2 x 10<sup>24</sup> atoms carbon Volume of gases are measured at '''standard temperature and pressure''' where the following conditions are met: (1) Temperature is zero degrees C (2) Pressure is 1.0 atm or 760 mm Hg For most gases at room temperature, the volume of 1 mole or the '''molar volume''' is 22.4 cubic decimeters at stp(22.4 dm<sup>3</sup>) which = 22.4 liters. See page 188 for an example.
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