CHAPTER 7 THE MOLE

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CHAPTER 7THE MOLE
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The mole (mol) is one of the seven base units in
the SI system. It measures the amount of
substance.
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The form in which a substance exists is its
representative particle.Representative
particles can be atoms, ions, molecules, formula
units, or anything else.
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Just as one dozen is 12 representative
particles, a mole is 6.02 x 1023 representative
particles.
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602,000,000,000,000,000,000,000!!!!!
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Examples1 mole Fe 6.02 x 1023 atoms of
Fe 1 mole H2O molecules 6.02 x 1023 molecules
of water1 mole Na ions 6.02 x 1023 Na
ions1 mole eggs 6.02 x 1023 eggs
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6.02 X 1023 Watermelon Seeds Would be found
inside a melon slightly larger than the
moon. 6.02 X 1023 Donut Holes Would cover the
earth and be 5 miles (8 km) deep. 6.02 X 1023
Pennies Would make at least 7 stacks that would
reach the moon. 6.02 X 1023 Grains of Sand
Would be more than all of the sand on Miami
Beach. 6.02 X 1023 Blood Cells Would be more
than the total number of blood cells found in
every human on earth.
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Diatomic ElementsCertain elements are only
stable in pairs or with other elements in a
compound. These elements are called the diatomic
elements.
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There are 7 diatomic elementsHydrogen,
bromine, oxygen, nitrogen, chlorine, iodine, and
fluorine(Memory trick H. BrONClIF or 7th
Heaven)
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Avogadros Number6.02 x 1023 is called
Avogadros number. It is named after Amadeo
Avogadro who did work in the 1800s that allowed
6.02 x 1023 to be calculated.
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The mole is the chemists dozen. It is a
convenient way to count extremely large numbers
of atoms, molecules or ions.
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New Conversion Factor! 1 mole 6.02 x 1023
representative particlesWe
work these problems using dimensional analysis.
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1. How many moles are 1.20 x 1025 atoms of
phosphorous?

• 1.20 x 1025 atoms P 1 mol P
  6.02 x 1023 atoms
• 19.9 mol P

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2. How many atoms are in 0.750 mol of Zn?

• 0.750 mol Zn 6.02 x 1023 atoms Zn
  1 mol Zn
• 4.52 x 1023 atoms Zn

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Q What did Avogadro teach his students in math
class? A Moletiplication
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3. How many molecules are in 0.400 mol N2O5?

• 0.400 mol N2O5 6.02 x 1023molecules
  1 mole N2O
• 2.41 x 1023 molecules

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4. How many moles are contained in 1.20 x 1024
molecules CO2?

• 1.20 x 1024 molec CO2 1 mol CO2
  6.02 x 1023
  molecules
• 1.99 moles CO2

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5. How many ammonium ions are in 0.036 mol
ammonium phosphate?

• 0.036 mol (NH4)3PO4 6.02 x 1023 f. u. (NH4)3PO4
  1 mole (NH4)3PO43
  NH4
• 1 f.u. (NH4)3PO4
• 6.5x 1022 NH4

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6. How many total carbon atoms are in a mixture
of 3.00 mol acetylene (C2H2) and 0.700 mol carbon
monoxide?

• 3.00 mol C2H2 6.02 x 1023 molec C2H2 2 C
  atoms 1 mol C2H2
  1 molec C2H2
• 3.61 x 1024 atoms C

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0.700 mol CO 6.02 x 1023 molec CO 1 C atom
1 mol CO
1 molec CO 4.21 x 1023 atoms C 3.61 x 1024
atoms 4.21 x 1023 atoms 4.03 x 1024 atoms C
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Gram atomic mass (gam) -atomic mass of an
element in grams-mass of one mole of atoms of a
monatomic element-use the periodic table and
take masses to 0.1 g
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Example C 12.0 g mass of 6.02 x 1023atoms
12.0 g/mol is the gram atomic mass of carbon

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Gram molecular mass (gmm) -mass of one mole of
a molecule-sum of the atomic masses of each atom
in the molecule
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1 mol H2O 2 mol H 1 mol O
2 x 1.0 g H/mol 2.0 g 1 x
16.0 g O/mol 16.0 g
18.0 g H2O
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7. What is the gram molecular mass of CH3OH?

• C 1 x 12.0 12.0
• H 4 x 1.0 4.0
• O 1 x 16.0 16.0
• 32.0 g

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Gram formula mass (gfm)-mass of one mole of an
ionic compound-sum of the atomic masses of each
atom in a formula unit
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8. What is the gfm of magnesium
phosphate?

• Mg3(PO4)2
• 3 mol Mg 3 x 24.3 g 72.9 g
• 2 mol P 2 x 31.0 g 62.0 g
• 8 mol O 8 x 16.0 g 128.0 g
• 262.9 g

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Gram formula mass is a generic term and can be
used for either ionic or molecular compounds.
Molar mass or molecular weight are terms also
used to mean the same thing.
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9. What is the molar mass of ammonium
sulfate?

• (NH4)2SO4
• 2 mol N 2 x 14.0 28.0
• 8 mol H 8 x 1.0 8.0
• 1 mol S 1 x 32.1 32.1
• 4 mol O 4 x 16.0 64.0
• 132.1 g

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Mole Mass ConversionsNew Conversion factor!
1 mol gfm
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10. Find the mass in grams of 3.32 mol of K.

• 3.32 mol K 39.1 g K 1 mol K
• 1.30 x 102 g K

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11. Find the mass in grams of 15.0 mol of
sulfuric acid.

• H2SO4
• H 2 x 1.0 2.0S 1 x 32.1 32.1O 4
  x 16.0 64.0 98.1 g
• 15.0 mol H2SO4 98.1 g H2SO4
  1 mol H2SO4
• 1470 g H2SO4

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12. Find the number of moles in 187 g of
aluminum.

• 187g Al 1 mol Al 27.0 g Al
• 6.93 mol Al

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13. Find the number of moles in 11.0 g of
methane (CH4).

• CH4 (12.0 4.0 16.0 g)
• 11.0 g CH4 1 mol CH4 16.0 g
  CH4
• 0.688 mol CH4

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14. Calculate the number of molecules present
in 4.29 g of nitrogen dioxide.

• 4.29g NO2 1 mol NO2 6.02 x 1023 NO2 molec
  46.0g NO2 1 mol NO2
• 5.61 x 1022 molecules NO2

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15. Calculate the number of moles of sulfur
atoms present in 2.01g of sodium sulfide.

• 2.01g Na2S 1mol Na2S 1 mol S atoms
  78.1g Na2S 1 mol Na2S
• 0.0257 mol S atoms

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16. Calculate the mass in grams of 2.49 x 1020
carbon dioxide molecules.2.49 x 1020 CO2 molec
1 mol CO2
6.02 x 1023 CO2 molec 44.0
g CO2 1mol CO2 0.0182 g CO2
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17. Calculate the grams of carbon in 12.2 mol of
sucrose, C12H22O11.12.2 mol C12H22O11 12 mol
C 12.0g C
1 mol C12H22O11 1 mol C1760 g C
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Molar Volume of a GasThe volume of a gas is
usually measured at 0oC and 1 atmosphere of
pressure. This is called standard temperature
and pressure (STP).
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-At STP, one mole of any gas has a volume of 22.4
L.-22.4 L is called the molar volume of a
gas.-22.4 L of a gas at STP contains 6.02 x
1023 particles of the gas.-22.4 L of a gas has
a mass equal to the gfm of the gas.
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New conversion factor! 1 mol of any gas at STP
22.4 L
(for gases only)
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18. What is the volume (liters) at STP of 0.960
mol of methane, CH4?

• 0.960 mol CH4 22.4 L CH4
  1 mol CH4
• 21.5 L CH4

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19. At STP, how many moles are in 0.542 mL of
neon gas?

• 0.542 mL Ne 1 L Ne 1 mol Ne
  1000 mL Ne 22.4 L Ne
• 2.42 x 10-5 mol Ne

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Gas DensityIf we know the density of a gas in
g/L at STP, we can calculate the gfm of the gas
(or visa versa)22.4 L/mol x density(g/L)
gfm
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20. The density of nitrogen gas at STP is 1.25
g/L. Find the gfm of nitrogen gas.

• 22.4 L 1.25 g
• 1 mol 1 L
• 28.0 g/mol N2

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21. Calculate the density of sulfur dioxide gas
at STP.

• SO2 64.1 g/mol
• 64.1gSO2 1 mol SO2
• 1 mol SO2 22.4 L SO2
• 2.86g/L

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Percent Composition(remember percent part
divided by total x 100)percent by mass of each
element in a compound of grams of the element
per 100 grams of the compound
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22. Find the composition for a compound that
is formed from 222.6 g of Na and 77.4 g O.

• 222.6g Na 77.4 g O 300.0 g total
• 222.6 g Na x 100 74.2 Na
• 300.0g total
• 77.4 g O x 100 25.8 O
• 300.0g total

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OR solve for percent composition from the
chemical formula mass grams of element in
1 mol of cmpd x 100
gfm of compound
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23. What is the percent composition of calcium
acetate?

• Ca(C2H3O2)2
• Ca 1 x 40.1 40.1
• C 4 x 12.0 48.0
• H 6 x 1.0 6.0
• O 4 x 16.0 64.0
• 158.1 g

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Ca (40.1/158.1) x 100 25.4 Ca C
(48.0/158.1) x 100 30.4C H (6.0/158.1) x
100 3.8H O (64.0/158.1) x 100
40.5O
100.1
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CALCULATING EMPIRICAL FORMULASEmpirical
formula - lowest whole number ratio of the
elements in a compound- may or may not be the
same as the molecular formula.
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Ex. H2O is both the empirical molecular
formula. H2O2 is a molecular formula. HO is
the empirical formula for H2O2.
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Steps to calculate empirical formula1. Find
moles of each element.2. Set up mole ratio.
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3. Simplify mole ratio (divide by smallest). If
your answers are not in whole numbers, you
must multiply by 2,3,4,or 5 to get whole
numbers.4. Use mole ratio as subscripts in the
formula. If given composition, assume 100 g of
compound.
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24. A compound is 79.8 C and 20.2 H. Find
its empirical formula.

• 79.8gC 1mol C 6.65 mol C
• 12.0 g C
• 20.2 g H 1 mol H 20.0 mol H
• 1.01 g H
• CH 6.65 20.0 1 3.0 6.65
  6.65
• CH3

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25. An oxide of aluminum is formed by
the complete reaction of 4.151g of aluminum with
3.692 g of oxygen. Calculate the empirical
formula for this compound.

• 4.151g Al 1 mol Al 0.1537 mol Al
  27.0 g Al
• 3.692g O 1 mol O 0.23075 mol O
  16.0 g O
• AlO 0.1537 0.23075 1 1.5 2 3
  0.1537
  0.1537
• Al2O3

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Molecular formulas are the actual formulas.
They may be the same as the empirical formula or
a multiple of it.
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To find the multiple (n), take the gram formulas
mass (gfm) and divide by the empirical formula
mass (efm) n gfm efm
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Multiply each subscript in the empirical formula
by n to get the molecular formula.
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26. A white powder is analyzed and found to
have the empirical formula P2O5. The compound
has a molar mass of 283.9 g. What is the
compounds molecular formula?

• P2O5 142.0 g/mol
• gfm/efm
• 283.9/142.0 2
• 2(P2O5) P4O10

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Ex. Complete combustion (reaction with O2) of a
sample of propane gas (contains only C H)
produced 2.641 g of CO2 and 1.442 g of water as
the only products. Find the empirical formula
for propane.

• 2.641g CO2 1 mol CO2 1 mol C 0.0600
  mol C 44.0 g CO2 1 mol CO2
• 1.442g H2O 1 mol H2O 2 mol H 0.160 mol H
  
  18.0g H2O 1 mol H2O
• CH 0.0600 0.160 1 2.67 3 8
  0.0600 0.0600
• C3H8

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A Mole Is a Unit A
mole is an animal that burrows in the ground,Or
a spot on your chin that you gotta shave
around.But there's another kind of mole of
interest to me,That's the kind of mole they use
in chemistry. Chorus A mole is a unit, or have
you heard,Containing six times ten to the
twenty-third,That's a six with twenty-three
zero's at the end,Much too big a number to
comprehend.
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Say you had a mole of pennies to distribute
'round the world,Give to each of the five
billion grownups, boys, and girls,There wouldn't
be a single person down and out of luck,Cause
everybody in the world would get a trillion
bucks. Or say you had a mole of paper and
stacked it toward the sky,Paper's awful thin,
but that pile would get so high.It'd reach up
into outer space, in fact I think you'd
find,It'd go up to the moon and back, eighty
billion times.
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Chorus A mole is a unit, or have you
heard,Containing six times ten to the
twenty-third,That's a six with twenty-three
zero's at the end,Much too big a number to
comprehend. Suppose a mole of marshmallows fell
upon the planet,Over each square inch of land
and sea, think that you could stand it?That
layer would be twelve miles high and of course
block our sun,We're talking close to five
million trillion tons.
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Well, maybe we could save ourselves if we all
started eaten',One marshmallow each second, not
two 'cause that'd be cheatin',With forty five
billion people munching, how long do you think
it'd take?Forty million years, and that's
without a bathroom break. Chorus A mole is a
unit, or have you heard,Containing six times ten
to the twenty-third,That's a six with
twenty-three zero's at the end,Much too big a
number to comprehend.
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But say you had a mole of atoms, would the pile
be immense,Should I say the answer now or leave
you in suspense?Well, atoms are so very small,
very small, you understand,You could hold a mole
of atoms in the palm of your hand. So shake a
little sugar in the middle of your palm,Now you
don't want to spill it, so try and stay calm.You
hardly can imagine and barely realize,There're
more atoms in that sugar than stars up in the sky.
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Chorus A mole is a unit, or have you
heard,Containing six times ten to the
twenty-third,That's a six with twenty-three
zero's at the end,Much too big a number to
comprehend.