Meet the Mole'

1
Meet the Mole.
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Moles

• The mole is a unit of measurement used in
  chemistry.
• The unit can be defined in multiple ways. (Well
  learn 3 today.)
• In its simplest terms, it represents a specific
  number.
• Dozen what number?
• Pair what number?
• Bakers dozen what number?
• Mole 6.022 x 1023

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Mole 6.022x1023

• Just like a dozen means 12 of anything...
  6.022x1023 of anything equals of mole.
• Consider the size of 6.022x1023. Is it large or
  small?
• Would you commonly use 6.022x1023 with large
  things or small things?

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Atoms, Elements, Compounds

• In chemistry, we are often dealing with VERY
  SMALL things.
• Atoms are SUBmicroscopic. In order to have an
  amount large enough with which to really
  interact, we need quite a few atoms. 6.022x1023
  is the number that Amadeo Avogadro chose in his
  lab using carbon.

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Avogadros Number

• 6.022x1023
• My pet mole is named Avogadro.

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Defining the Mole

• Counting
• Weighing
• Amount of Space Needed
• Lets represent our 3 mole definitions in a
  graphic organizer.

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Learning to Use the Mole Map

• Using the Mole Concept to Calculate
• Page 182-4
• EX 6.3, EX 6.4
• PP 6.4

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Example 6.3

• Aluminum (Al), a metal with a high
  strength-to-weight ratio and a high resistance to
  corrosion, is often used for structures such as
  high-quality bicycle frames. Compute both the
  number of moles of atoms and the number of atoms
  in a 10.0-g sample of aluminum.
• Read the prompt for
• A question
• A starting point for the solution
• Extra information to be set aside

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Example 6.3

• Aluminum (Al), a metal with a high
  strength-to-weight ratio and a high resistance to
  corrosion, is often used for structures such as
  high-quality bicycle frames. Compute both the
  number of moles of atoms and the number of atoms
  in a 10.0-g sample of aluminum.
• Read the prompt for
• A question (Unknown)
• A starting point for the solution (Given)
• Extra information to be set aside
• How many calculations is this prompt asking me to
  carry out?
• Concentrate on one calculation at a time
• Continue work on the board.

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Example 6.4

• A silicon chip used in an integrated circuit of a
  computer has a mass of 5.68 mg. How many silicon
  (Si) atoms are present in this chip? The average
  atomic mass for silicon is 28.09 amu.

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Example 6.4

• A silicon chip used in an integrated circuit of a
  computer has a mass of 5.68 mg. How many silicon
  (Si) atoms are present in this chip? The average
  atomic mass for silicon is 28.09 amu.
• Read the prompt for
• A question (Unknown)
• A starting point for the solution (Given)
• Extra information to be set aside
• How many calculations is the prompt asking me to
  carry out?
• Set up the calculation.
• Continue work on the board.

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Practice Problem 6.4

• Chromium (Cr) is a metal that is added to steel
  to improve its resistance to corrosion (for
  example, to make stainless steel). Calculate
  both the number of moles in a sample of chromium
  containing 5.00 x 1020 atoms and the mass of the
  sample.

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Independent Practice

• CH 6 Assessment
• (pg 210 14-15)

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Moles Mass of Compounds

• A compound is a collection of atoms.
• To calculate the mass of one mole of a compound,
  youd need to add up the mass of all the atoms.
  This is called the MOLAR MASS.
• Example 1 mole CH4 ______ g CH4
• 1 C 12.011 g C
• 4 H 4(1.0079 g H)
• Total 16.04 g/mol

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Example 6.5

• Calculate the molar mass of sulfur dioxide, a gas
  produced when sulfur-containing fuels are burned.
• SO2
• S 32.07 g
• O 2(16.00 g)
• Total 64.07 g/mol
• Can also be expressed as 1 mol SO2 64.07 g

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Practice Problems 6.5

• Polyvinyl chloride, called PVC, which is widely
  used for floor coverings (vinyl) as well as for
  plastic pipes in plumbing systems, is made form a
  molecule with the formula C2H3Cl. Calculate the
  molar mass of this substance.
• 62.49 g/mol

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If we know that mass moles are related...

• Lets look at our mole maps again.
• Where would molar mass be added to our mole maps?
• Molar mass is a conversion factor (a
  relationship) between moles and mass.
• Molar mass can be used to convert units from
  moles to mass or vice versa.

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Example 6.6

• Calcium carbonate, CaCO3 (also called calcite),
  is the principal mineral found in limestone,
  marble, chalk, pearls, and the shells of marine
  animals.
• Calculate the molar mass of calcium carbonate.
• A certain sample of calcium carbonate contains
  4.86 mol. What is the mass in grams of this
  sample?
• How many calculations are we being asked to do?
• Follow the example on the board.

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Practice Problem 6.6

• Calculate the molar mass for sodium sulfate,
  Na2SO4. A sample of sodium sulfate with a mass
  of 300.0 g represents what number of moles of
  sodium sulfate?
• Identify the given and the unknown.
• What is the conversion factor on the mole map?
• Set up the calculation.

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Example 6.7

• Juglone, a dye known for centuries, is produced
  from the husks of black walnuts. It is also a
  natural herbicide that kills off competitive
  plants around the black walnut tree but does not
  affect grass and other noncompetitive plants.
  The formula for juglone is C10H6O3.
• Calculate the molar mass of juglone.
• A sample of 1.56 g of pure juglone was extracted
  from black walnut husks. How many moles of
  juglone does this sample represent?

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Partner Practice

• Pg 190-1
• Example 6.8
• Practice Problem 6.8

Independent Practice

• CH 6 Assessment (pg 211 21-23)

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Molar Volume

• If converting between the units of moles and
  liters of a gas, what conversion factor is
  needed?
• 1 mole ________________
• 1 mole 22.4 Liters
• Example During cellular respiration, a cell
  releases 2.1 mol of O2 gas. What volume is
  needed to hold that gas?

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Thinking Critically About Moles

• Knowledge Level Station
• Show your knowledge of the mole concept by
  labeling the Mole Map graphic organizer.
• Use the colored pencils to color-code your
  organizer.
• RED COUNTING PARTICLES
• BLUE WEIGHING SUBSTANCES
• GREEN AMOUNT OF SPACE TAKEN BY A GAS

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Thinking Critically About Moles

• Comprehension Level Station
• Explain the use of the mole map to your partner.
  Use the following calculation prompts in your
  explanation. Begin your explanation with I
  would use my mole map to solve this calculation
  by...
• Partner One How many grams of sucrose,
  C12H22O11 contain 0.79 moles?
• Partner Two The number of particles in 0.91
  moles of ammonia is _____.

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Thinking Critically About Moles

• Application Level Station
• Use the conversion factors illustrated and
  explained on the Mole Map to compute solutions to
  the following. Show all of your work.
• Calculate the number of grams of cobalt that
  contain the same number of atoms as 2.24 g of
  iron.
• Apply the concept of the mole in order to
  determine which of the following statements is
  the most accurate description of a mole.
• The number of atoms in 55.85 grams of iron.
• The mass of carbon in a measured sample of
  carbon.
• The number of atoms in any given mass of a
  molecule.
• 6.022 x1023 grams of a sample of any element.

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Thinking Critically About Moles

• Analysis Level Station
• Use the substances and instruments at the
  station. Which substance will create a taller
  column in the graduated cylinder 0.215 mol
  C12H22O11 or 0.972 mol NaHCO3? Measure and record
  the height of each in mL.
• Compare the molar masses of the two substances.
• If 7 balloons were filled with the 1 mole of each
  of the 7 diatomic gases, which balloon would
  weigh the most? The least?

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Thinking Critically About Moles

• Synthesis/Evaluation Level Station
• Evaluate the calculations shown. Is vital
  information missing? Is dimensional analysis set
  up correctly? Correct each incorrect
  calculation.
• See Ms. Moore for a Whats wrong here is...
  focus. On the poster paper provided, prepare a
  detailed description of the
• Mistake
• Correction
• Resulting answer

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Percent Composition

• The relative amounts of each element in a
  compound are expressed in percent composition.
  AKA percent by mass of each element
• of element grams of element X 100
• grams of compound

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Example 6.9

• Carvone is a substance that occurs in two forms,
  both of which have the same molecular formula
  (C10H14O) and molar mass. One type of carvone
  give caraway seeds their characteristic smell
  the other is responsible for the smell of
  spearmint oil. Compute the mass percent of each
  element in carvone.

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Percent by Mass Worksheet

• Individually, calculate the mass percents of the
  first three compounds on the worksheet.

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Connecting Moles Mass to Chemical Formulas

• Mass is easily related to chemical formulas
• The relationship of moles to chemical formulas
  requires a little more thought...

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Type of Chemical Formula Empirical Formula

• Empirical formula lowest whole number ratio of
  the atoms of the elements in a compound
• Ionic compounds are criss-crossed and then
  reduced. Ionic compound formulas are nearly
  always empirical formulas.
• Empirical formula doesnt have to be the same as
  the actual molecular formula of the compound.

33
Empirical Formula

• CH2O
• Calculate the mass percent of each element.
• C 40
• H 6.7
• O 53.3
• Isnt this the reduced formula for C3H6O3,
  C4H8O4, C5H10O5, C6H12O6
• The mass percent of each of these compounds is
  the same.

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Type of Chemical Formula Molecular Formula

• Molecular formula actual formula for the
  compound which gives the composition of the
  molecule
• Glucose shares an empirical formula with many
  compounds, but it has its molecular formula all
  to itself.
• 6(CH2O) glucose

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Calculating Empirical Formulas

• When an unknown compound is found, instruments
  can tell scientists the mass percent composition
  of the compound.
• Calculations are required to convert that series
  of percentages into a chemical formula.
• We start by converting to the empirical formula.

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Calculating Empirical Formula

• Use a simple rhyme!
• to gram
• Gram to mole
• Divide by the smallest
• Multiply til whole.

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Example 6.11

• An oxide of aluminum is formed by the reaction of
  4.151 g of aluminum with 3.692 g of oxygen.
  Calculate the empirical formula for this
  compound.
• to gram IS DONE FOR YOU
• Gram to mole dimensional analysis
• Lets carry out the calculation on the board.

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Example 6.13

• A sample of lead arsenate, an insecticide used
  against the potato beetle, contains 1.3813 g of
  lead, 0.00672 g of hydrogen, 0.4995 g of arsenic,
  and 0.4267 g of oxygen. Calculate the empirical
  formula for lead arsenate.

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Example 6.14

• The most common form of nylon is 63.68 carbon,
  12.38 nitrogen, 9.80 hydrogen, and 14.4
  oxygen. Calculate the empirical formula for
  nylon.

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Calculating Molecular Formula

• Molecular Formula n(empirical formula)
• (Remember 6(CH2O) glucose)
• We know how to calculate the empirical formula,
  but how do we know what number to multiply it by?
• n molecular formula mass/molar mass of empirical

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Example 6.15

• A white powder is analyzed and found to have an
  empirical formula of P2O5. The compound has a
  molar mass of 283.88 g/mol. What is the
  compounds molecular formula?

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Practice Problem 6.15

• A compound used as an additive for gasoline to
  help percent engine knock shows the following
  percentage composition
• 71.65 Cl
• 24.27 C
• 4.07 H
• The molar mass is known to be 98.96 g. Determine
  the empirical formula and the molecular formula
  for this compound.

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Individual Practice

• Page 208 4-6