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THE MOLE

THE MOLE. We can ’ t work with individual atoms or amu ’ s in the lab…..Why not?? Because we cannot see things that small !. Dude !!!! Atoms are REALLY REALLY small !!. We work with samples large enough for us to SEE and WEIGH on a balance using units of grams. This creates a problem….

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THE MOLE

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  1. THE MOLE

  2. We can’t work with individual atoms or amu’s in the lab…..Why not?? Because we cannot see things that small ! Dude !!!! Atoms are REALLY REALLY small !!

  3. We work with samples large enough for us to SEE and WEIGH on a balance using units of grams.

  4. This creates a problem….. A pile of atoms big enough for us to see contains BILLIONS OF ATOMS !!!!

  5. SOOOOO…chemists made up a new unit…. THE MOLE

  6. A mole is the SI base unit used to measure the amount of a substance. - Its abbreviation is mol. WHAT IS A MOLE???

  7. Why is this unit necessary in chemistry? It connects the world we can’t see to a world we can measure !!!!

  8. HOLY MOLE-Y ! A mole is the mass of a substance that contains a certain number of molecules (or atoms). • For example, a MOLE of carbon weighs 12 grams and is made up of…. 6.022 x 1023 particles !

  9. If I had a dozen eggs…..how many do I have?

  10. Just like a dozen represents 12….A mole represents 6.022 X 1023items, whatever they may be. • 1 mol H atoms = 6.022 x 1023 H atoms • 1 mol electrons = 6.022 x 1023 electrons • 1 mol pennies = 6.022 x 1023 pennies

  11. This number 6.022 x 1023 (NA) is known as Avogadro’s number and is one of the most fundamental constants in the field of chemistry. One mole of a substance contains 6.022 x 1023molecules.

  12. Just How Big is a Mole? • Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles. • If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole. • If a mole of pennies were evenly distributed among the world’s population, each of us would have enough money to spend $1 million dollars every hour – day and night – and still have one half of it unspent at the time of our death.

  13. Avogadro’s Number as Conversion Factor 6.02 x 1023 particles 1 mole or 1 mole 6.02 x 1023 particles Note that a particle could be an atom OR a molecule!

  14. Learning Check 1. Number of atoms in 0.500 mole of Al a) 500 Al atoms b) 6.02 x 1023 Al atoms c) 3.01 x 1023 Alatoms 2.Number of moles of S in 1.8 x 1024 S atoms a) 1.0 mole S atoms b) 3.0 mole S atoms c) 1.1 x 1048 mole S atoms

  15. Molar mass: the sum of atomic masses of all the atoms shown by the formula of a substance Use the periodic table to find the needed atomic weights EXAMPLE: Water (H2O) Atom# Atoms x Atomic Weight H 2 x 1.0 amu O 1 x 16.0 amu Molar mass = 2(1.0) + 1(16.0) = 18.0 grams/mole = 18.0 g/mol A mole can also be calculated by the molar mass.

  16. The molar mass, in grams per mole, is numerically equal to the sum of the masses (in amu) of the atoms in the formula.

  17. Other Names Related to Molar Mass • Molecular Mass/Molecular Weight: If you have a single molecule, mass is measured in amu’s instead of grams. But, the molecular mass/weight is the same numerical value as 1 mole of molecules. Only the units are different. (This is the beauty of Avogadro’s Number!) • Formula Mass/Formula Weight: Same goes for compounds. But again, the numerical value is the same. Only the units are different. • THE POINT: You may hear all of these termswhich mean the SAME NUMBER… just different units

  18. Learning Check! Find the molar mass (usually we round to the tenths place) = 79.9 g/mole • 1 mole of Br atoms • 1 mole of Sn atoms = 118.7g/mole

  19. Molar Mass of Molecules and Compounds Mass in grams of 1 mole equal numerically to the sum of the atomic masses 1 mole of CaCl2 = ????? 1 mole Ca x 40.1 g/mol + 2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl2

  20. Learning Check! • Molar Mass of K2O = ? Grams/mole 94.2 g/mol

  21. Learning Check Prozac, C17H18F3NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. Find its molar mass. 309.4 g/mol

  22. Calculations with Molar Mass molar mass Grams Moles

  23. Converting Moles and Grams Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al ? g Al

  24. 1. Molar mass of Al 1 mole Al = 27.0 g Al 2. Conversion factors for Al 27.0g Al or 1 mol Al 1 mol Al 27.0 g Al 3. Setup3.00 moles Al x 27.0 g Al 1 mole Al Answer = 81.0 g Al

  25. Learning Check! The artificial sweetener aspartame (Nutra-Sweet) formula C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? .765 mol

  26. Atoms/Molecules and Grams • Since 6.02 X 1023 particles = 1 mole AND1 mole = molar mass (grams) • You can convert atoms/molecules to moles and then moles to grams! (Two step process) • You can’t go directly from atoms to grams!!!! You MUST go thru MOLES. • That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first!

  27. Calculations molar mass Avogadro’s numberGrams Moles particles Everything must go through Moles!!!

  28. Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu 1 mol Cu 6.02 X 1023 atoms Cu 63.5 g Cu 1 mol Cu = 3.36 X 1023 atoms Cu

  29. IMPORTANT TO REMEMBER! • A mole always represents a certain number of items, 6.022 x 1023. Its mass, however, differs with the substance involved. • A mole of H2O, (18.02 g), weighs considerably more than a mole of H2, (2.016), even though they contain the same number of molecules!

  30. Learning Check! How many atoms of K are present in 78.4 g of K? 1.21 x 1024 atoms K

  31. Learning Check! What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)? 359 g glucose

  32. THE END

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