Transcript Chapter 6

Chapter 6
Chemical Quantities
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How you measure how much?
You can measure mass,
 or volume,
 or you can count pieces.
 We measure mass in grams.
 We measure volume in liters.
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We count pieces in MOLES.
Moles
Defined as the number of carbon
atoms in exactly 12 grams of carbon12.
 1 mole is 6.02 x 1023 particles.
 Treat it like a very large dozen
 6.02 x 1023 is called Avogadro’s
number.
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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.
 For an element it is an atom.
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Types of questions

How many oxygen atoms in the
following?
– CaCO3
– Al2(SO4)3
 How many ions in the following?
– CaCl2
– NaOH
– Al2(SO4)3
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Types of questions
How many molecules of CO2 are the in
4.56 moles of CO2 ?
 How many moles of water is 5.87 x 1022
molecules?
 How many atoms of carbon are there in
1.23 moles of C6H12O6 ?
 How many moles is 7.78 x 1024 formula
units of MgCl2?
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Measuring Moles
Remember relative atomic mass?
 The amu was one twelfth the mass
of a carbon 12 atom.
 Since the mole is the number of
atoms in 12 grams of carbon-12,
 the decimal number on the periodic
table is also the mass of 1 mole of
those atoms in grams.
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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 1.008 grams of
hydrogen and 55.85 grams of iron.
 We can write this as
12.01 g C = 1 mole
 We can count things by weighing
them.
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Examples
How much would 2.34 moles of
carbon weigh?
 How many moles of magnesium in
24.31 g of Mg?
 How many atoms of lithium in 1.00 g
of Li?
 How much would 3.45 x 1022 atoms
of U weigh?
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What about compounds?
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in 1 mole of H2O molecules there are two
moles of H atoms and 1 mole of O atoms
To find the mass of one mole of a
compound
– determine the moles of the elements
they have
– Find out how much they would weigh
– add them up
What about compounds?
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 molecular mass of CH4 is 16.05g
 The mass of one mole of a molecular
compound.
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Gram Formula Mass
The mass of one mole of a compound.
 Calculated the same way.
 What is the GFM of Fe2O3?
 2 moles of Fe x 55.85 g = 111.70 g
 3 moles of O x 16.00 g = 48.00 g
 The GFM = 111.70 g + 48.00 g = 159.70g
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Molar Mass
The generic term for the mass of one
mole.
 The same as molecular mass, gram
formula mass, and gram atomic
mass.
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Examples
Calculate the molar mass of the
following and tell me what type it is.
 Na2S
 N2O4
C
 Ca(NO3)2
 C6H12O6
 (NH4)3PO4
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Using Molar Mass
Finding moles of compounds
Counting pieces by weighing
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Molar Mass
The number of grams of 1 mole of
atoms, ions, or molecules.
 We can make conversion factors
from these.
 To change grams of a compound to
moles of a compound.
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For example
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How many moles is 5.69 g of NaOH?
For example

How many moles is 5.69 g of NaOH?

5.69 g
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


For example

How many moles is 5.69 g of NaOH?
mole 

5.69 g


g 
 need to change grams to moles
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For example

How many moles is 5.69 g of NaOH?
mole 

5.69 g


g 
 need to change grams to moles
 for NaOH
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For example

How many moles is 5.69 g of NaOH?
mole 

5.69 g


g 
 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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For example
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How many moles is 5.69 g of NaOH?
mole 

5.69 g


g 
 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
For example
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How many moles is 5.69 g of NaOH?
1 mole 

5.69 g


40.00 g 
 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
For example

How many moles is 5.69 g of NaOH?

5.69 g

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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1 mole 
 = 0.142 mol NaOH
40.00 g 
Examples
How many moles is 4.56 g of CO2 ?
 How many grams is 9.87 moles of
H2O?
 How many molecules in 6.8 g of
CH4?
 49 molecules of C6H12O6 weighs how
much?
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