Chemistry: Matter and Change

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Chapter Menu
The Mole
Section 10.1 Measuring Matter Section 10.2 Mass
and the Mole Section 10.3 Moles of
Compounds Section 10.4 Empirical and Molecular
Formulas Section 10.5 Formulas of Hydrates
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Section 10-1
Section 10.1 Measuring Matter

• Explain how a mole is used to indirectly count
  the number of particles of matter.

molecule two or more atoms that covalently bond
together to form a unit

• Relate the mole to a common everyday counting
  unit.
• Convert between moles and number of
  representative particles.

mole Avogadros number
Chemists use the mole to count atoms, molecules,
ions, and formula units.
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Section 10-1
Counting Particles

• Chemists need a convenient method for accurately
  counting the number of atoms, molecules, or
  formula units of a substance.

• The mole is the SI base unit used to measure the
  amount of a substance.
• 1 mole is the amount of atoms in 12 g of pure
  carbon-12, or 6.02 ? 1023 atoms.
• The number is called Avogadros number.

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Section 10-1
Converting Between Moles and Particles

• Conversion factors must be used.

• Moles to particles

Number of molecules in 3.50 mol of sucrose
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Section 10-1
Converting Between Moles and Particles (cont.)

• Particles to moles

• Use the inverse of Avogadros number as the
  conversion factor.

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Section 10-1
Section 10.1 Assessment
What does the mole measure? A. mass of a
substance B. amount of a substance C. volume of
a gas D. density of a gas

1. A
2. B
3. C
4. D

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Section 10-1
Section 10.1 Assessment

1. A
2. B
3. C
4. D

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End of Section 10-1
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Section 10-2
Section 10.2 Mass and the Mole

• Relate the mass of an atom to the mass of a mole
  of atoms.

conversion factor a ratio of equivalent values
used to express the same quantity in different
units

• Convert between number of moles and the mass of
  an element.
• Convert between number of moles and number of
  atoms of an element.

molar mass
A mole always contains the same number of
particles however, moles of different substances
have different masses.
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Section 10-2
The Mass of a Mole

• 1 mol of copper and 1 mol of carbon have
  different masses.

• One copper atom has a different mass than 1
  carbon atom.

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Section 10-2
The Mass of a Mole (cont.)

• Molar mass is the mass in grams of one mole of
  any pure substance.

• The molar mass of any element is numerically
  equivalent to its atomic mass and has the units
  g/mol.

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Section 10-2
Using Molar Mass

• Moles to mass

3.00 moles of copper has a mass of 191 g.
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Section 10-2
Using Molar Mass (cont.)

• Convert mass to moles with the inverse molar mass
  conversion factor.

• Convert moles to atoms with Avogadros number as
  the conversion factor.

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Section 10-2
Using Molar Mass (cont.)

• This figure shows the steps to complete
  conversions between mass and atoms.

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Section 10-2
Section 10.2 Assessment
The mass in grams of 1 mol of any pure substance
is A. molar mass B. Avogadros number
C. atomic mass D. 1 g/mol

1. A
2. B
3. C
4. D

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Section 10-2
Section 10.2 Assessment
Molar mass is used to convert what? A. mass to
moles B. moles to mass C. atomic weight
D. particles

1. A
2. B
3. C
4. D

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End of Section 10-2
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Section 10-3
Section 10.3 Moles of Compounds

• Recognize the mole relationships shown by a
  chemical formula.

• Calculate the molar mass of a compound.
• Convert between the number of moles and mass of a
  compound.
• Apply conversion factors to determine the number
  of atoms or ions in a known mass of a compound.

representative particle an atom, molecule,
formula unit, or ion
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Section 10-3
Section 10.3 Moles of Compounds (cont.)
The molar mass of a compound can be calculated
from its chemical formula and can be used to
convert from mass to moles of that compound.
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Section 10-3
Chemical Formulas and the Mole

• Chemical formulas indicate the numbers and types
  of atoms contained in one unit of the compound.

• One mole of CCl2F2 contains one mole of C atoms,
  two moles of Cl atoms, and two moles of F atoms.

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Section 10-3
The Molar Mass of Compounds

• The molar mass of a compound equals the molar
  mass of each element, multiplied by the moles of
  that element in the chemical formula, added
  together.

• The molar mass of a compound demonstrates the law
  of conservation of mass.

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Section 10-3
Converting Moles of a Compound to Mass

• For elements, the conversion factor is the molar
  mass of the compound.

• The procedure is the same for compounds, except
  that you must first calculate the molar mass of
  the compound.

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Section 10-3
Converting the Mass of a Compound to Moles

• The conversion factor is the inverse of the molar
  mass of the compound.

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Section 10-3
Converting the Mass of a Compound to Number of
Particles

• Convert mass to moles of compound with the
  inverse of molar mass.

• Convert moles to particles with Avogadros number.

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Section 10-3
Converting the Mass of a Compound to Number of
Particles (cont.)

• This figure summarizes the conversions between
  mass, moles, and particles.

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Section 10-3
Section 10.3 Assessment
How many moles of OH ions are in 2.50 moles of
Ca(OH)2? A. 2.00 B. 2.50 C. 4.00 D. 5.00

1. A
2. B
3. C
4. D

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Section 10-3
Section 10.3 Assessment
How many particles of Mg are in 10 moles of
MgBr2? A. 6.02 ? 1023 B. 6.02 ? 1024 C. 1.20
? 1024 D. 1.20 ? 1025

1. A
2. B
3. C
4. D

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End of Section 10-3
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Section 10-4
Section 10.4 Empirical and Molecular Formulas

• Explain what is meant by the percent composition
  of a compound.

percent by mass the ratio of the mass of each
element to the total mass of the compound
expressed as a percent

• Determine the empirical and molecular formulas
  for a compound from mass percent and actual mass
  data.

percent composition empirical formula molecular
formula
A molecular formula of a compound is a
whole-number multiple of its empirical formula.
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Section 10-4
Percent Composition

• The percent by mass of any element in a compound
  can be found by dividing the mass of the element
  by the mass of the compound and multiplying by
  100.

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Section 10-4
Percent Composition (cont.)

• The percent by mass of each element in a compound
  is the percent composition of a compound.

• Percent composition of a compound can also be
  determined from its chemical formula.

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Section 10-4
Empirical Formula

• The empirical formula for a compound is the
  smallest whole-number mole ratio of the elements.

• You can calculate the empirical formula from
  percent by mass by assuming you have 100.00 g of
  the compound. Then, convert the mass of each
  element to moles.
• The empirical formula may or may not be the same
  as the molecular formula.
• Molecular formula of hydrogen peroxide H2O2
• Empirical formula of hydrogen peroxide HO

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Section 10-4
Molecular Formula

• The molecular formula specifies the actual number
  of atoms of each element in one molecule or
  formula unit of the substance.

• Molecular formula is always a whole-number
  multiple of the empirical formula.

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Section 10-4
Molecular Formula (cont.)
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Section 10-4
Section 10.4 Assessment
What is the empirical formula for the compound
C6H12O6? A. CHO B. C2H3O2 C. CH2O D. CH3O

1. A
2. B
3. C
4. D

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Section 10-4
Section 10.4 Assessment
Which is the empirical formula for hydrogen
peroxide? A. H2O2 B. H2O C. HO D. none of
the above

1. A
2. B
3. C
4. D

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End of Section 10-4
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Section 10-5
Section 10.5 Formulas of Hydrates

• Explain what a hydrate is and relate the name of
  the hydrate to its composition.

crystal lattice a three-dimensional geometric
arrangement of particles

• Determine the formula of a hydrate from
  laboratory data.

hydrate
Hydrates are solid ionic compounds in which water
molecules are trapped.
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Section 10-5
Naming Hydrates

• A hydrate is a compound that has a specific
  number of water molecules bound to its atoms.

• The number of water molecules associated with
  each formula unit of the compound is written
  following a dot.
• Sodium carbonate decahydrate Na2CO3 10H2O

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Section 10-5
Naming Hydrates (cont.)
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Section 10-5
Analyzing a Hydrate

• When heated, water molecules are released from a
  hydrate leaving an anhydrous compound.

• To determine the formula of a hydrate, find the
  number of moles of water associated with 1 mole
  of hydrate.

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Section 10-5
Analyzing a Hydrate (cont.)

• Weigh hydrate.

• Heat to drive off the water.
• Weigh the anhydrous compound.
• Subtract and convert the difference to moles.
• The ratio of moles of water to moles of anhydrous
  compound is the coefficient for water in the
  hydrate.

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Section 10-5
Use of Hydrates

• Anhydrous forms of hydrates are often used to
  absorb water, particularly during shipment of
  electronic and optical equipment.

• In chemistry labs, anhydrous forms of hydrates
  are used to remove moisture from the air and keep
  other substances dry.

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Section 10-5
Section 10.5 Assessment
Heating a hydrate causes what to happen?
A. Water is driven from the hydrate. B. The
hydrate melts. C. The hydrate conducts
electricity. D. There is no change in the
hydrate.

1. A
2. B
3. C
4. D

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Section 10-5
Section 10.5 Assessment
A hydrate that has been heated and the water
driven off is called A. dehydrated compound
B. antihydrated compound C. anhydrous compound
D. hydrous compound

1. A
2. B
3. C
4. D

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End of Section 10-5
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Resources Menu
Chemistry Online Study Guide Chapter
Assessment Standardized Test Practice Image
Bank Concepts in Motion
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Study Guide 1
Section 10.1 Measuring Matter
Key Concepts

• The mole is a unit used to count particles of
  matter indirectly. One mole of a pure substance
  contains Avogadros number of particles.

• Representative particles include atoms, ions,
  molecules, formula units, electrons, and other
  similar particles.
• One mole of carbon-12 atoms has a mass of exactly
  12 g.
• Conversion factors written from Avogadros
  relationship can be used to convert between moles
  and number of representative particles.

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Study Guide 2
Section 10.2 Mass and the Mole
Key Concepts

• The mass in grams of 1 mol of any pure substance
  is called its molar mass.

• The molar mass of an element is numerically equal
  to its atomic mass.
• The molar mass of any substance is the mass in
  grams of Avogadros number of representative
  particles of the substance.
• Molar mass is used to convert from moles to mass.
  The inverse of molar mass is used to convert from
  mass to moles.

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Study Guide 3
Section 10.3 Moles of Compounds
Key Concepts

• Subscripts in a chemical formula indicate how
  many moles of each element are present in 1 mol
  of the compound.

• The molar mass of a compound is calculated from
  the molar masses of all of the elements in the
  compound.
• Conversion factors based on a compounds molar
  mass are used to convert between moles and mass
  of a compound.

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Study Guide 4
Section 10.4 Empirical and Molecular Formulas
Key Concepts

• The percent by mass of an element in a compound
  gives the percentage of the compounds total mass
  due to that element.

• The subscripts in an empirical formula give the
  smallest whole-number ratio of moles of elements
  in the compound.
• The molecular formula gives the actual number of
  atoms of each element in a molecule or formula
  unit of a substance.
• The molecular formula is a whole-number multiple
  of the empirical formula.

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Study Guide 5
Section 10.5 Formulas of Hydrates
Key Concepts

• The formula of a hydrate consists of the formula
  of the ionic compound and the number of water
  molecules associated with one formula unit.

• The name of a hydrate consists of the compound
  name and the word hydrate with a prefix
  indicating the number of water molecules in 1 mol
  of the compound.
• Anhydrous compounds are formed when hydrates are
  heated.

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Chapter Assessment 1
What does Avogadros number represent? A. the
number of atoms in 1 mol of an element B. the
number of molecules in 1 mol of a compound
C. the number of Na ions in 1 mol of NaCl (aq)
D. all of the above

1. A
2. B
3. C
4. D

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Chapter Assessment 2
The molar mass of an element is numerically
equivalent to what? A. 1 amu B. 1 mole C. its
atomic mass D. its atomic number

1. A
2. B
3. C
4. D

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Chapter Assessment 3
How many moles of hydrogen atoms are in one mole
of H2O2? A. 1 B. 2 C. 3 D. 0.5

1. A
2. B
3. C
4. D

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Chapter Assessment 4
What is the empirical formula of Al2Br3?
A. AlBr B. AlBr3 C. Al2Br D. Al2Br3

1. A
2. B
3. C
4. D

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Chapter Assessment 5
What is an ionic solid with trapped water
molecules called? A. aqueous solution
B. anhydrous compound C. hydrate D. solute

1. A
2. B
3. C
4. D

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STP 1
Two substances have the same percent by mass
composition, but very different properties. They
must have the same ____. A. density
B. empirical formula C. molecular formula
D. molar mass

1. A
2. B
3. C
4. D

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STP 2
How many moles of Al are in 2.0 mol of Al2Br3?
A. 2 B. 4 C. 6 D. 1

1. A
2. B
3. C
4. D

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STP 3
How many water molecules are associated with 3.0
mol of CoCl2 6H2O? A. 18 B. 1.1 ? 1025
C. 3.6 ? 1024 D. 1.8 ? 1024

1. A
2. B
3. C
4. D

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STP 4
How many atoms of hydrogen are in 3.5 mol of
H2S? A. 7.0 ? 1023 B. 2.1 ? 1023 C. 6.0 ?
1023 D. 4.2 ? 1024

1. A
2. B
3. C
4. D

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STP 5
Which is not the correct formula for an ionic
compound? A. CO2 B. NaCl C. Na2SO4 D. LiBr2

1. A
2. B
3. C
4. D

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IB 6
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IB 7
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CIM
Figure 10.6 Molar Mass Table 10.1 Formulas of
Hydrates
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