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 1023. There are 6.02 x 1023 hydrogen atoms in 1 gram atomic mass of hydrogen, 6.02 x 1023 oxygen atoms in 1 gram atomic mass of oxygen and so on. The number 6.02 x 1023 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 1023 atoms
Oxygen (O2): 1 mole, 1 gram atomic mass, 32 grams, 6.02 x 1023 molecules
Water (H2O): 1 mole, 1 gram atomic mass, 18 grams, 6.02 x 1023 molecules
Dry Ice (CO2): 1 mole, 1 gram atomic mass, 44 grams, 6.02 x 1023 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 1023 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 1023 formula units
Example: What is the mass of 1.0 mol of H2O?
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 1024 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 dm3) which = 22.4 liters. See page 188 for an example.