Dimensional Analysis, the Mole Concept, and Avogadro

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Dimensional Analysis, the Mole Concept, and
Avogadros ConstantTopic 1.1
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Dimensional Analysis

• starting with one unit of measurement and ending
  up with a different one
• cancel out what you dont want
• use conversion factors (fraction that equals one)
• the numerator will contain the unit you want
• the denominator will contain the unit you are
  trying to get rid of
• try to predict a ball park answer if possible
  so you might recognize a wrong answer

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(No Transcript)
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• sometimes they can be done in one step
• example 23,532 seconds ? minutes
• 23,532 sec. X 1 min.
• 1 60 sec.
• 392.20 min.

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• sometimes they take multiple steps
• example 23,532 seconds ? hours
• 23,532 sec. X 1 min. X 1 hour
• 1 60 sec. 60 min.
• 6.5367 hours

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• but if you dont know the conversion factor(s),
  the problem becomes impossible
• example 750 ml ? fl oz
• 750 ml X 1 fl oz
• 1 29.6 ml
• 25.3 fl oz

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How many minutes are in 2.5 hours?

• Initial unit
• 2.5 hr
• Conversion Final
• factor unit
• 2.5 hr x 60 min 150 min
• 1 hr
• cancel Answer (2 SF)

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• What is wrong with the following setup?
• 1.4 day x 1 day x 60 min x 60
  sec
• 24 hr 1 hr
  1 min

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• 1.4 day x 1 day x 60 min x 60
  sec
• 24 hr 1 hr
  1 min
• Units day2/hr2 Not the final unit needed

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Topic 1.1 really starts here
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Measuring Matter

• By counting
• simply a number or moles
• By determining the mass
• grams
• By determining the volume
• liters

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Not these!
The Mole
Not this!
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• the mole is a unit used in chemistry to represent
  a large number of particles such as
• atoms (Ne, Ar)
• molecules (H2O, CO2)
• ionic compounds (NaCl, MgCl2)
• ions (Mg2, Cl1-)
• similar to a dozen, except instead of 12, its
  602 billion trillion
• 6.02 x 1023 or 602,214,199,000,000,000,000,000
• known as Avogadros number

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• 1 dozen cookies 12 cookies
• 1 mole of cookies 6.02 X 1023 cookies
• 1 dozen cars 12 cars
• 1 mole of cars 6.02 X 1023 cars
• 1 dozen Al atoms 12 Al atoms
• 1 mole of Al atoms 6.02 X 1023 atoms
• Note that the NUMBER is always the same, but the
  MASS would be very different!
• Mole is abbreviated mol (gee, thats a lot
  quicker to write, huh?)

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• 1 mole C
• 6.02 x 1023 C atoms
• 1 mole water
• 6.02 x 1023 H2O molecules
• 1 mole NaCl
• 6.02 x 1023 NaCl ionic compounds
• 6.02 x 1023 Na ions
• 6.02 x 1023 Cl ions

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Note that a particle could be an atom OR a
compound/molecule!

• for counting in chemistry, the conversion factor
  will be
• 1 mole
• 6.02 x 1023 particles
• OR
• 6.02 x 1023 particles
• 1 mole

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Number of particles to moles

• How many moles in 5.68 x 1025 fluorine molecules?
• 5.68 x 1025 molecules x _____1 mole____
• 1 6.02 x
  1023 molecules

94.4 mol F2
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• How many moles of water in 7.77x1024 molecules of
  water?
• 7.77 x 1024 molecules x 1mole
• 6.02x1023 molecules
• 12.9 moles H2O

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Number of moles to particles

• How many atoms in 5.59 moles of He?
• 5.59 moles x 6.02 x 1023 atoms
• 1 1 mole

3.36 x 1024 atoms

• How many atoms in 2.98 moles of H20 molecules?
• 2.98 moles x 6.02 x 1023 molecules H2O x
  3 atoms
• 1 1 mole
  1 molecule H2O
• 5.38 x 1024 atoms