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Atomic Masses & the MOLE…

Atomic Masses & the MOLE…. Atomic Mass. Masses of atoms expressed in grams are extremely small. An atom of O-16 literally weighs 0.0000000000000000000000266 g For most calculations in chemistry it is easier to use a relative atomic mass.

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Atomic Masses & the MOLE…

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  1. Atomic Masses & the MOLE…

  2. Atomic Mass • Masses of atoms expressed in grams are extremely small. • An atom of O-16 literally weighs 0.0000000000000000000000266 g • For most calculations in chemistry it is easier to use a relative atomic mass. • For relative masses, the carbon atom was arbitrarily chosen as the standard, by which all other masses are compared

  3. 6 C CARBON 12 Atomic Mass • The mass of all the other atoms are then expressed in relation to the standard • C-12 atom acts as the standard • A single C-12 atom was assigned a mass of 12 atomic mass units (amu)

  4. The Mole • The mole, whose abbreviation is “mol”, is the SI base unit for meas-uring the amount of a pure substance. • 1 mol = 6.02 x 1023 items • Many objects in our everyday lives come in similar counting units. • 1 ream = 500 sheets of paper • 1 pair of socks = 2 socks

  5. The Mole • Avogadro’s Number (6.02 x 1023) is the number of particles in exactly one mole of a pure substance • Avogardro‘s Number = 1 mole • The mole becomes a counting unit much like the dozen. • 1 dozen eggs = 12 eggs • 1 mole of eggs = 602,000,000,000,000,000,000,000 eggs

  6. How Big is 6.02 x 1023? • Avogadro’s # of sand- • spread evenly over the entire state of California would have a layer of sand as high as a 10 story building • Avogadro’s # of marshmallows • spread evenly over all 50 states would equal a blanket of marshmallows more than 600 miles deep. • Avogadro’s # of pennies distributed to 4 billion people • Would give each one enough money to spend a million $ every hour, day and night throughout his lifetime and still would not spend half of it (humanity could not survive buried under all those pennies more than 50 miles deep

  7. CHEMICAL REP. PARTICLE SUBTANCE REPRESENTATIVE FORMULA PARTICLE IN 1 MOL

  8. The Mole Using the mole in calculations #1 How many moles of Magnesium is 1.25 x 1023 atoms of Magnesium? 1 mole Mg 1.25x1023 atoms Mg 6.02x1023atoms Mg = .208 mol Mg

  9. 23 18.99g F atoms=1 mol F atoms=6.02x10 F atoms Molar Mass • Molar Mass or Gram Molar Mass is equal to the mass of 1 mole(or 6.02x1023 ) of a pure substance • 1 mole is = to the molar mass from the Periodic Table • 1 mol of C atoms weighs 12.01 g • 1 mol of H atoms weighs 1.008 g • 1 mol of W atoms weigh 183.8 g

  10. Molar Mass • What is the mass of 1 mole of Sulfur Trioxide (SO3) A.K.A. Molar Mass? • You can calculate the mass of a molecule of SO3 by adding the MM of each of the atoms in the molecule • The mass of 1 mole of S is 32.1g. • The mass of 3 atoms of O is 3 times the MM of a single O atom,or(3)(15.99g) = 47.97g • So MM of 1 molecule of SO3 is 32.1g + 47.97g = 80.1 g/mol

  11. Molar Mass What is the MM of glucose (C6H12O6)? (6C’S)(12.011g/mol) = 72.066g/mol (12H’S)(1.008 g/mol) = 12.096g/mol 95.94g/mol (6O’S)(15.99 g/mol) = 180.1g/mol 1 mole of C6H12O6 or 6.02x1023 molecules of the compound – it would weigh 180 grams

  12. Practice Time: • Determine the mass of 1 mole (Molar mass) of each of the following: • Zn(C2H3O2)2 • (1 Zn atom)(65.4 g/mol) = 65.4 g/mol • (4 C atoms)(12.0 g/mol)= 48.0 g/mol • (6 H atoms)(1.0 g/mol) = 6.0 g/mol • (4 O atoms)(16.0 g/mol) = 64.0 g/mol • 183.4 g/mol

  13. Using the mole in calculations How many grams are in 9.45 mol of Dinitrogen Trioxide (N2O3) (2N’s)(14.01 g) = 28.02 g (3O’s)(15.99) = 47.97 g 75.99 g If 1 mol of Dinitrogen Trioxide weighs 75.99 grams, than how much does 9.45 moles of the substance weigh?

  14. Using the Mole in calculations Step 2: Convert the given moles to grams using the Molar mass equality. 75.99 g N2O3 9.45 mol N2O3 1 mol N2O3 =718 g N2O3

  15. Molar Volume of a Gas 22.4 L 22.4 L 1 mole of any gas under the specific conditions of 0°C and 1 atm (STP) will occupy a volume of 22.4 L. 6.02x1023 molecules of CO2 6.02x1023 molecules of O2

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