AP Chemistry
Chapter 3
Concepts
Details
Atomic
Mass
A. C-12, the Relative Standard



B. Atomic Mass (Average atomic mass, atomic weight)



The average Mass of an Element
When a sample of natural copper is vaporized and injected
into a mass spectrometer, the results shown are obtained.
Use these data to compute the average mass of natural copper.
(The mass values for 63Cu and 65Cu are 62.93 amu and 64.93
amu.)
The Mole
A. Avagadro’s number


Measuring moles

Compute both number of moles and number of atoms in a 10.0gram sample of Aluminum.
A silicon chip used in an integrated circuit of a
microcomputer has a mass of 5.68 mg. How many (Si) atoms are
present in the chip.
Cobalt (Co) is a metal that is added to steel to improve its
resistance to corrosion. Calculate both the number of moles
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AP Chemistry
Chapter 3
in a sample of cobalt contained 5.00 x 1020 atoms and the
mass of the sample.
Molar
Mass
A. Molar Mass (Gram Molecular Weight)


Juglone, a dye known for centuries, is produced from the
husks of black walnuts. It is also a natural herbicide (weed
killer) that kills of competitive plants around the black
walnut tree but does not affect grass or other noncompetitive plants. The formula of Juglone is C10H6O3.
 Calculate the molar mass of juglone
 A sample of 1.56 x 10-2 grams of pure juglone was
extracted from the black walnut husks. How many moles
does this represent?
Calcium carbonate (CaCO3), also called calcite, is the
principal mineral found is limestone, marble, chalk, pearls,
and the shells of marine animals such as clams.
 Calculate the molar mass of calcium carbonate.
 A certain sample of calcium carbonate contains 4.86
moles. What is the mass in grams of this sample? What
is the mass of the CO32- ions present?
Percent
Composi
tion
A. Calculating any percentage –
B. Percentage Composition –
Carvone is a substance that occurs in two forms having
different arrangements of the atoms but the same molecular
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AP Chemistry
Chapter 3
formula (C10H14O) and mass. One type of carvone gives caraway
seeds their characteristic smell, and the other type is
responsible for the smell of spearmint oil. Compute the mass
percent in each element in carvone.
Determini
ng the
formula
of a
compoun
d
A. Determining the empirical formula




B. Determining the molecular formula



Determine the empirical and molecular formulas for a compound
that gives the following percentages upon analysis (in mass
percents).
71.65% Cl, 24.27% C, 4.07% H
The molar mass is known to be 98.96 g/mol.
A white powder is analyzed and found the contain 43.64%
phosphorous and 56.36% oxygen my mass. The compound has a
molar mass of 283.88 g/mol. What are the compound’s
empirical and molecular formulas?
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AP Chemistry
Chapter 3
Chemical
Equatio
ns
A. Chemical Reactions



B. The meaning of a Chemical Reaction

a)
b)
c)
d)
Blancing
Chemica
l
Equatio
ns

A. Dtermine what reaction is happening

B. Write the unbalanced equation

C. Balance the equation by inspection

D. Include phase formation

At 1000C, ammonia gas, NH3 (g), reacts with
form gaseous nitric oxide, NO (g), and water
reaction is the first step in the commercial
nitric acid by the Ostwald process. Balance
this reaction.
Stoichiom
etric
Calcula
tions:
Amounts
of
Reactan
oxygen gas to
vapor. This
production of
the equation for
Steps
 Write a balanced equation
 Set up a BCA table
 If necessary, change grams to moles
 Fill in BCA Table
 If necessary, change moles to grams to obtain final
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AP Chemistry
Chapter 3
ts and
Product
s
answer.
Solid Lithium hydroxide is used in space vehicles to remove
exhaled carbon dioxide from the living environment by forming
solid lithium carbonate and liquid water. What mass of
gaseous carbon dioxide can be absorbed by 1.00 kg of lithium
hydroxide?
Baking Soda (NaHCO3) is often used as an antacid. It
neutralizes excess hydrochloric acid secreted by the stomach:
NaHCO3 (s) + HCl (aq)  NaCl (aq) + H2O (l) + CO2 (aq)
Milk of magnesia, which is an aqueous suspension of magnesium
hydroxide, is also used as an antacid:
Mg(OH)2 (s) + HCl (aq)  2 H2O (l)
+ MgCl2 (aq)
Which is a more effective antacid per gram, NaHCO3 or Mg(OH)2?
Calculati
ons
involvi
ng a
Limitin
A. Concept of Limiting Reactant

–
B. Solving Limiting Reactant Problems

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AP Chemistry
Chapter 3
g
Reactan
t


C. Calculating Percent Yield


Nitrogen gas can be prepared by passing gaseous ammonia over
solid copper (II) oxide at high temperatures. The other
products of the reaction are solid copper and water vapor.
If a sample containing 18.1 grams of NH3 is reacted with 90.4
grams of CuO, which is the limiting reactant? How many grams
of N2 will be formed?
Percent
Yield
Actual Yield –
Theoretical Yield –
Equation:
Methanol (CH3OH) is the simplest alcohol. It is used as fuel
in racecars and is a potential replacement for gasoline.
Methanol can be manufactured by combination of gaseous carbon
monoxide and hydrogen. Suppose 68.5 kg of CO(g) is reacted
with 8.60 kg of H2(g). Calculate the theoretical yield of
methanol. If 3.57 x 104 g CH3OH is actually produced, what
is the percent yield of methanol?
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AP Chemistry
Chapter 3
Challengin
g
Empirical
Formula
Problem
When hydrocarbons are burned in a limited amount of
oxygen, both CO and CO2 form. When .450 grams of a
particular hydrocarbon was burned in air, 0.467 g of
CO2, and .450 g of H2O were formed.
 What is the empirical formula of the compound?
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