Chemical Quantities

1
Chapter 7

• Chemical Quantities

2
Representative Particles

• The smallest pieces of a substance.
• For a molecular compound it is a molecule.
• For an ionic compound it is a formula unit (a set
  of ions).
• For an element it is an atom.

3
Counting Ions

• How many ions in the following?
• 1) CaCl2
• 3 ions 1 Ca and 2 Cl
• 2) NaOH
• 2 ions 1 Na and 1 OH
• 3) Al2(SO4)3
• 5 ions 2 Al and 3 SO4

4
Counting Atoms

• How many oxygen atoms are in the following?
• 1) CaCO3
• 3 oxygen atoms
• 2) Al2(SO4)3
• 12 oxygen atoms

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Moles

• Defined as the number of carbon atoms in exactly
  12 grams of carbon-12.
• 1 mole is 6.02 x 1023 particles.
• Treat it like a very large dozen
• 6.02 x 1023 is called Avogadros number.

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Gram Atomic Mass

• The mass of 1 mole of an element in grams.
• 12.01 grams of carbon has the same number of
  pieces as 1.01 grams of hydrogen and 55.85 grams
  of iron.
• 12.01 g C 1 mole C
• Allows us to count things by weighing them.
• Atomic Masses found on Periodic Table

7
Gram Formula Mass

• The mass of one mole of an ionic compound.
• What is the GFM of Fe2O3?
• 2 atoms Fe x 55.85 g 111.70 g
• 3 atoms O x 16.00 g 48.00 g
• GFM 111.70 g 48.00 g 159.70g

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Gram Molecular Mass

• Finding the mass of a molecular compound.
• Calculated the same as GFM.
• What is the mass of one mole of CH4?
• 1 mole of C 12.01 g
• 4 mole of H x 1.01 g 4.04g
• 1 mole CH4 12.01 4.04 16.05g
• The Gram Molecular mass of CH4 is 16.05g

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Molar Mass

• The generic term for the mass of one mole.
• The same as gram molecular mass, gram formula
  mass, and gram atomic mass.
• DO NOT WRITE MOLAR MASSES IN SCIENTIFIC NOTATION!

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Examples 1 and 2

• Calculate the molar mass of the following.
• 1)Na2S
• Na 2 x 22.99 45.98
• S 1x 32.06 32.06
• Molar Mass 78.04 grams
• 2)N2O4 C
• N 2 x 14.01 28.02
• O 4 x 16.00 64.00
• C 1 x 12.01 12.01
• Molar Mass 104.03 grams

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Example 3

• Ca(NO3)2
• Ca 1 x 40.08 40.08
• N 2 x 14.01 28.02
• O 6 x 16.00 96.00
• Molar Mass 164.10 grams

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Example 4

• C6H12O6
• C 6 x 12.01 72.06
• H 12 x 1.01 12.12
• O 6 x 16.00 96.00
• Molar Mass 180.18 g

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Example 5

• (NH4)3PO4
• N 3 x 14.01 42.03
• H 12 x 1.01 12.12
• P 1 x 30.97 30.97
• O 4 x 16.00 64.00
• Molar Mass 149.12 g

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Converting to Mass from Moles

• One Step Problems

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Molar Mass

• The number of grams in 1 mole of atoms, ions, or
  molecules.
• We can make conversion factors from these.
• Use to change grams of a compound to moles of a
  compound.

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Example 1

• How many moles is 5.69 g of NaOH?

17
Example 1

• How many moles is 5.69 g of NaOH?

18
Example 1

• How many moles is 5.69 g of NaOH?

• need to change grams to moles

19
Example 1

• How many moles is 5.69 g of NaOH?

• need to change grams to moles
• for NaOH

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Example 1

• How many moles is 5.69 g of NaOH?

• need to change grams to moles
• for NaOH
• 1mole Na 22.99g 1 mol O 16.00 g 1 mole of
  H 1.01 g

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Example 1

• How many moles is 5.69 g of NaOH?

• need to change grams to moles
• for NaOH
• 1mole Na 22.99g 1 mol O 16.00 g 1 mole of
  H 1.01 g
• 1 mole NaOH 40.00 g

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Example 1

• How many moles is 5.69 g of NaOH?

• need to change grams to moles
• for NaOH
• 1mole Na 22.99g 1 mol O 16.00 g 1 mole of
  H 1.01 g
• 1 mole NaOH 40.00 g

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Example 1

• How many moles is 5.69 g of NaOH?

• need to change grams to moles
• for NaOH
• 1mole Na 22.99g 1 mol O 16.00 g 1 mole of
  H 1.01 g
• 1 mole NaOH 40.00 g

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Example 2

• How many grams is 9.87 moles of H2O?
• 9.87 mol H2O x 18.02 g H2O
• 1 mol H2O
• 1.78 x 102 g H2O

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Example 3

• How many moles of magnesium in 24.31 g of Mg?
• 24.31 g Mg x 1 mol Mg
• 24.31 g Mg
• 1 mol Mg

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Example 4

• How much would 2.34 moles of carbon weigh (in g)?
  
• 2.34 mol C x 12.01 g C
• 1 mol C
• 2.81 x 101 g C

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Converting to Atoms Molecules from Moles

• One step problems
• For elements
• 1 mole 6.02 x 1023 atoms
• For molecular compounds
• 1 mole 6.02 x 1023 molecules
• For ionic compounds
• 1 mole 6.02 x 1023 formula units

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Example 1

• 1) How many molecules of CO2 are there in 4.56
  moles of CO2 ?
• 4.56 moles x 6.02 x 1023 molecules
• 1 mole
• 2.75 x 1024 molecules CO2

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Example 2

• How many moles of water is 5.87 x 1022 molecules?
  
• 5.87 x 1022 molecules x 1 mole
• 6.02 x 1023 molec
• 9.75 x 10-2 moles water

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Example 3

• How many moles is 7.78 x 1024 formula units of
  MgCl2?
• 7.78 x 1024 for. un. MgCl2 x 1 mole MgCl2
• 6.02 x 1023 for.un. MgCl2
• 1.29 x 101 mole MgCl2

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Watch out for this one!

• How many atoms of carbon are there in 1.23 moles
  of C6H12O6 ?
• 1.23 mol C6H12O6 x 6.02 x 1023 molec C6H12O6 x 6
  atoms C
• 1 mol C6H12O6 1 molec C6H12O6
• 4.44 x 1024 atoms C

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2 Step Problems

• Converting from
• Mass to atoms
• Molecules to mass
• Mass to molecules
• Atoms to mass
• Formula units to mass
• Mass to formula units

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Example 1

• How many atoms of lithium in 1.00 g of Li?
• 1.00 g Li x 1 mol Li x 6.02 x 1023 atoms Li
• 6.94g Li 1 mol Li
• 8.67 x 1022 atoms Li

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Example 2

• How much would 3.45 x 1022 atoms of U weigh in
  grams?
• 3.45 x 1022 atoms U x 1 mol U x 238.03 g U
• 6.02 x 1023 atoms U 1 mol U
• 1.36 x 101 g U

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Example 3

• How many molecules in 6.8 g of CH4?
• 6.8 g CH4 x 1 mol CH4 x 6.02 x 1023 molec CH4
• 16.05 g CH4 1 mol CH4
• 2.55 x 1023 molec CH4

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Example 4

• 49 molecules of C6H12O6 weighs how many grams?
• 49 molec C6H12O6 x 1 mol C6H12O6 x
  180.18 g C6H12O6
• 6.02 x 1023 molec C6H12O6
  1 mol C6H12O6
• 1.47 x 10-20 g C6H12O6

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Gases and the Mole
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Gases

• Many of the chemicals we deal with are gases.
• They are difficult to weigh.
• Need to know how many moles of gas we have.
• Two things effect the volume of a gas Temperature
  and pressure
• Compare at the same temp. and pressure.

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Standard Temperature and Pressure

• 25ºC and 1 atm pressure
• abbreviated STP
• At STP 1 mole of gas occupies 22.4 L
• Called the molar volume
• Avogadros Hypothesis - at the same temperature
  and pressure equal volumes of gas have the same
  number of particles.

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Example 1

• What is the volume of 4.59 mole of CO2 gas at
  STP?
• 4.59 mol CO2 x 22.4 L CO2
• 1 mol CO2
• 1.03 x 102 L CO2

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Example 2

• How many moles is 5.67 L of O2 at STP?
• 5.67 L O2 x 1 mol O2
• 22.4 L O2
• 2.53 x 10-1 mol O2

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Example 3

• What is the volume of 8.80g of CH4 gas at STP?
• 8.80 g CH4 x 1 mol CH4 x 22.4 L CH4
• 16.05 g CH4 1 mol CH4
• 1.23 x 101 L CH4

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Density of a Gas

• D m /V
• for a gas the units will be g / L
• We can determine the density of any gas at STP if
  we know its formula.
• To find the density we need the mass and the
  volume.
• If you assume you have 1 mole than the mass is
  the molar mass (PT)
• At STP the volume is 22.4 L.

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Examples

• 1) Find the density of CO2 at STP.
• D m/v
• D 44.01 g /22.4 L
• D 1.96 x 100 g/L
• 2) Find the density of CH4 at STP.
• D m/v
• D 16.05 g/22.4 L
• D 7.17 x 10-1 g/L

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The other way

• Given the density, we can find the molar mass of
  the gas.
• Again, pretend you have a mole at STP, so V
  22.4 L.
• m D x V
• m is the mass of 1 mole, since you have 22.4 L of
  the stuff.

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Examples

• 1)What is the molar mass of a gas with a density
  of 1.964 g/L?
• m d x v
• m 1.964 g/L x 22.4 L
• m 4.40 x 101 g
• 2) What is the molar mass of a gas with a
  density of 2.86 g/L?
• m d x v
• m 2.86 g/L x 22.4 L
• m 6.41 x 101 g

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We have learned how to change

• change moles to grams
• moles to atoms
• moles to formula units
• moles to molecules
• moles to liters
• molecules to atoms
• formula units to atoms
• formula units to ions

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Mass
Moles
49
Mass
PT
Moles
50
Mass
Volume
PT
Moles
51
Mass
Volume
22.4 L
PT
Moles
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Mass
Volume
22.4 L
PT
Moles
Representative Particles
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Mass
Volume
22.4 L
PT
Moles
6.02 x 1023
Representative Particles
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Mass
Volume
22.4 L
PT
Moles
6.02 x 1023
Representative Particles
Atoms
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Mass
Volume
22.4 L
PT
Moles
6.02 x 1023
Representative Particles
Molecules or Ions
Atoms
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Equivalencies

• 1 mole 6.02 x 1023 particles
• 1 mole molar mass (g)
• 1 mole 22.4 L (gas at STP)
• Since these are all equal, they can all be used
  as conversion factors.

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Good Luck!!!

• Youre gonna need it!!!?