To Do…
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http://chem.illinois.edu
Lab tomorrow. Read Chapter 13.
Lon-Capa (HW2 Type 2 due
Wednesday, February 5 by 7 pm).
1
Polyatomic Ions
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Ammonium
Nitrate
Sulfate
Hydroxide
Phosphate
Carbonate
2
The Mole Concept: Why?
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We can count by weighing (relative
masses).
Reactions occur by number of particles,
we must deal with masses, so we must
have a way of converting between
number and mass.
Atoms/molecules are very small!
3
Calculate…
You have 50.0 g of water.
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How many moles of H2O molecules
do you have?
How many moles of hydrogen atoms
are present in this sample?
4
Consider This…
Does a methane molecule (CH4) contain more
hydrogen or more carbon?
5
Clicker Question
Determine the percent by mass of hydrogen in a
sample of 2 moles of methane (CH4).
a) 12.57% by mass hydrogen
b) 25.13% by mass hydrogen
c) 50.26% by mass hydrogen
d) I have no idea.
6
Clicker Question
Determine the percent by mass of hydrogen in a
sample of 2 moles of methane (CH4).
a) 12.57% by mass hydrogen
b) 25.13% by mass hydrogen
c) 50.26% by mass hydrogen
7
Calculate…
Determine the percent mass of oxygen in
each of the following substances:
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H2O (water)
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H2O2 (hydrogen peroxide)
8
Determining a Formula
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You have some “nitrogen oxide”
compound and you want to figure
out what it is (both the formula and
the name). You know it’s 30.4%
nitrogen by mass.
NxOy = formula?
name?
9
Calculate…
Determine the percent mass of nitrogen
in:
dinitrogen tetroxide
10
Calculate…
Octane (a constituent of gasoline) is a
hydrocarbon (consists only of carbon and
hydrogen). It has a molar mass of about
114 g/mol and is 84.12% carbon by
mass.
Determine the molecular formula for
octane.
11
Calculate…
You have equal masses of each of the
following compounds:
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Sulfuric acid: H2SO4
Sucrose (table sugar): C12H22O11
Potassium chlorate: KClO3
Which one has the greatest number of
oxygen atoms?
12
Formulas for Ionic Compounds
are Empirical Formulas
13