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Honors Chemistry The Mole & Avogadro’s Number Notes Name ______________________________ Period ____ Measuring Matter Substances react according to definite ratios of numbers of particles (atoms, ions, formula units, or molecules). The following balanced chemical equation shows that two atoms of aluminum react with three molecules of iodine to form two formula units of aluminum iodide. 2Al(s) + 3I2(s) 2AlI3(s) If you wanted to carry out this reaction, how could you measure the correct numbers of particles of aluminum and iodine? Fortunately, you can count particles by measuring mass. Suppose you have a sample of an element, and the mass of the sample in grams is numerically equal to the atomic mass of the element. Scientists have discovered that this mass of an element contains 6.02 x 1023 atoms of that element. This number is called Avogadro’s number. Avogadro’s number of particles is called a mole of particles. The mole is the SI base unit used to measure the amount of a substance and is defined as the number of particles in exactly 12 g of pure carbon-12. For the purpose of dealing with moles, the simplest unit of any substance is called a representative particle. The particle may be an atom, a molecule, a formula unit, or an ion. Example Problem 1: Converting Moles to Number of Particles How many molecules are in 2.25 moles of bromine? Bromine is an element that consists of diatomic molecules. Therefore, one mole of bromine contains 6.02 x 10 23 Br2 molecules. To find the number of Br2 molecules present in 2.25 mol, multiply the number of moles by Avogadro’s number. number of Br2 molecules = 2.25 mol x 6.02 x 1023 molecules Br2 1 mol number of Br2 molecules = 1.35 x 1024 molecules Br2 Example Problem 2: Converting Particles to Moles Calculate the number of moles in a sample of sodium bromide that contains 2.88 x 1023 formula units. Because 1 mol NaBr = 6.02 x 1023 formula units NaBr, you can see that 2.88 x 1023 formula units is less than one mole of NaBr. moles of NaBr = 2.88 x 1023 formula units x 1 mol NaBr 6.02 x 1023 formula units moles of NaBr = 0.478 mol NaBr The Mole & Avogadro’s Number Notes Additional Notes/Examples Notetaking Counting Units: Measuring a Mole - Counting Atoms (Molecules): How big is a mole? One mole of popcorn: One mole of stacked pennies: One mole of marshmallows: History of Avogadro’s Number Avogadro – 1811: Cannizzaro – 1861: Ostwald – 1902: 1971: The Law of Conservation of Mass According to the Law of Conservation of Mass, Mass of reactants = mass of products Mass of starting substances = mass of ending substances So the production of one water molecule requires: Therefore, And The Law of Definite Proportions and Ratios of Atoms Law of Definite Proportions: Example: Moles Particles Conversions: Examples Conversions: 1) 3.5 moles to atoms 2) 18.06 x 1023 atoms to moles Convert from moles to particles: 3) 2.7 moles to particles 4) 4.32 x 1024 atoms to moles 5) 5.3 moles of bromine 6) 4.7 moles of potassium oxide Convert from particles to moles: 7) 4.32 x 1024 atoms of calcium 8) 2.7 x 1020 atoms of copper 9) 2.5 x 1024 molecules of sodium chloride 10) 5.32 x 1023 molecules of calcium chloride You try these: 10) 25 moles to particles 11) 4.08 x 104 particles to moles 12) 0.002 moles to particles 13) 2.3 x 1016 particles Practice Problems: 1. Calculate the number of molecules in 15.7 mol carbon dioxide. 2. Calculate the number of molecules in 0.0544 mol H2O. 3. Calculate the number of moles in 9.22 x 1023 atom iron. 4. Calculate the number of moles of sucrose in a sample that contains 2.05 x 1022 sucrose molecules. 5. A student uses 0.0850 mol copper sulfate to carry out a reaction. If the reaction uses up 0.0832 mol copper sulfate, how many formula units are left unreacted? Honors CHEMISTRY Moles Particles Conversions WS I Use the factor label method to convert the following on your own sheet of paper. Circle your answers. Moles to Particles: Particles to Moles: 1. 1.8 moles to particles 1. 2.7 x 1020 atoms to moles 2. 5.3 moles to atoms 2. 2.5 x 1024 molecules to moles 3. 4.7 moles to atoms 3. 5.32 x 1023 atoms to moles 4. 25 moles to molecules 4. 4.08 x 1014 particles to moles 5. 0.0018 moles to atoms 5. 2.3 x 1016 atoms to moles Honors CHEMISTRY Moles Particles Conversions II WS Use the factor label method to convert the following on your own sheet of paper. Circle your answers. Moles to Particles: Particles to Moles: 1. 10.6 moles to particles 1. 6.9 x 1022 atoms to moles 2. 2.4 moles to atoms 2. 7.3 x 1024 molecules to moles 3. 0.75 moles to atoms 3. 4.18 x 1023 atoms to moles 4. 18 moles to molecules 4. 2.5 x 1019 particles to moles 5. 0.039 moles to atoms 5. 1.67 x 1021 atoms to moles