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Formula Weight & Molecular Weight

Formula Weight & Molecular Weight. The FORMULA WEIGHT of a compound equals the SUM of the atomic masses of the atoms in a formula. If the formula is a molecular formula, the formula weight is also called the MOLECULAR WEIGHT. The MOLE.

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Formula Weight & Molecular Weight

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  1. Formula Weight & Molecular Weight • The FORMULA WEIGHT of a compound equals the SUM of the atomic masses of the atoms in a formula. • If the formula is a molecular formula, the formula weight is also called the MOLECULAR WEIGHT.

  2. The MOLE • Amount of substance that contains an Avogadro’s number (6.02 x 10 23)of formula units.

  3. The MOLE • The mass of 1 mole of atoms, molecules or ions = the formula weight of that element or compound in grams. Ex. Mass of 1 mole of water is 18 grams so molar mass of water is 18 grams/mole.

  4. Formula for Mole Mole = mass of element formula weight of element

  5. Sample Mole Calculations 1 mole of C = 12.011 grams • 12.011 gm/mol • 0.5 mole of C = 6.055 grams • 12.011 gm/mol

  6. Avogadro’s Number • Way of counting atoms • Avogadro’s number = 6.02 x 1023

  7. Point to Remember One mole of anything is 6.02 x 1023 units of that substance.

  8. And…….. • 1 mole of C has the same number of atoms as one mole of any element

  9. Formula Weight & Molecular Weight • The FORMULA WEIGHT of a compound equals the SUM of the atomic masses of the atoms in a formula. • If the formula is a molecular formula, the formula weight is also called the MOLECULAR WEIGHT.

  10. Summary • Avogadro’s Number gives the number of particles or atoms in a given number of moles • 1 mole of anything = 6.02 x 10 23 atoms or particles

  11. Sample Problem 2 • Compute the number of atoms and moles of atoms in a 10.0 gram sample of aluminum.

  12. Solution • PART I: • Formula for Mole: • Mole = mass of element atomic mass of element

  13. Solution (cont.) • Part II: To determine # of atoms • # atoms = moles x Avogadro’s number

  14. Problem # 2 • A diamond contains 5.0 x 1021 atoms of carbon. How many moles of carbon and how many grams of carbon are in this diamond?

  15. Molar Mass • Often referred to as molecular mass • Unit = gm/mole • Definition: • mass in grams of 1 mole of the compound

  16. Example Problem • Determine the Molar Mass of C6H12O6

  17. Solution • Mass of 6 mole C = 6 x 12.01 = 72.06 g • Mass of 12 mole H = 12 x 1.008 = 12.096 g • Mass of 6 mole O = 6 x 16 = 96.00 g • Mass of 1 mole C6H12O6 = 180.16 g

  18. Problem #3 • What is the molar mass of (NH4)3(PO4)?

  19. Molar Mass • Often referred to as molecular mass • Unit = gm/mole • Definition: • mass in grams of 1 mole of the compound

  20. Sample Problem • Given 75.99 grams of (NH4)3(PO4), determine the ff: • 1. Molar mass of the compound • 2. # of moles of the compound • 3. # of molecules of the compound • 4. # of moles of N • 5. # of moles of H • 6. # of moles of O • 7. # of atoms of N • 8. # of atoms of H • 9. # of atoms of O

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