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Factor-Label Method

Factor-Label Method. Math technique used for conversion problems. Not the same as the proportion technique. More powerful in multistep problems. Changing Units. In the factor-label method, you use a conversion factor to express the quantity in the desired units.

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Factor-Label Method

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  1. Factor-Label Method • Math technique used for conversion problems. • Not the same as the proportion technique. • More powerful in multistep problems.

  2. Changing Units • In the factor-label method, you use a conversion factor to express the quantity in the desired units. • Set up your calculation so the units cancel out.

  3. If you have 8 dozen eggs, how many eggs do you have?  That’s the given information. 8 Doz eggs X 12 eggs = 96 eggs 1 Doz eggs  That’s the answer. That’s the conversion factor.

  4. Another Example of the Factor-Label Method • How many quarts are in 3.5 gallons? • Equality you know: 1 gallon = 4 quarts. • Format = Given X Conversion Factor = Ans • Conversion Factor is a ratio built from the equalities. You put it together so the units cancel out. The value of the ratio is “one.”

  5. Gallons to Quarts • 3.5 Gallons X 4 Quarts = 14 Quarts 1 Gallon Identify the given, the conversion factor, and the answer.

  6. Number of Moles in Sample • The mass of an iron bar is 27.9 g. How many moles of Fe are in the sample? • What equalities do you know? • 1 mole of Fe = • 55.8 g Fe = • 6.02 X 1023 atoms Fe

  7. formula mass 22.4 L/mol 6.02 X 1023

  8. Factor-Label Method • Format = Given X Conversion Factor = Ans • 27.9 g Fe X 1 Mole Fe = 0.5 Mole Fe 55.8 grams Fe

  9. Formula Mass of a Compound • Sum of the atomic masses for all the atoms present. • CO2 has a formula mass of: • 12.0 amu + 16.0 amu + 16.0 amu = 44.0 amu

  10. Molar Mass of any Compound • = Formula mass expressed in grams. • 1 mole of NaCl = 58.5 grams NaCl • 1 mole of CO2 = 44.0 grams of CO2 • 1 mole of H2O = 18.0 grams of H2O • 1 mole of CaCO3 = 100. grams of CaCO3 • 1 mole of LiF = 25.9 grams of LiF

  11. Mole  Mass Conversions • Conversion factor comes from an equality you build from the periodic table.

  12. Mole - # of particle Conversions • 1 equality, so it’s easier. • 1 mole of anything = 6.02 X 1023 of that thing

  13. Mole - # of Particle Conversions • How many particles are in 3 moles of He? Given = 3 moles of He Equality: 1 mole of He molecules = 6.02 X 1023 molecules of He Format: Given X Ratio = Ans 3 moles He molecules X 6.02 X 1023 molecules = 1 mole of He molecules

  14. 18 X 1023 molecules!

  15. # of Particles to Moles • How many moles are in 3.01 X 1023 particles of Ar? Given: 3.01 X 1023 particles of Ar Equality: 1 mole = 6.02 X 1023 particles 3.01 X 1023 particles X 1 mole = 6.02 X 1023 particles

  16. 0.5 moles!

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