Chapter 7:
Chemical Quantities
• The Mole: A Measurement of Matter
• Mole-Mass and Mole-Volume
Relationships
• Percent Composition and Chemical
Formulas
Chapter 7: Chemical Quantities
The Mole:
A Measurement of Matter
Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- The Mole: A Measurement of Matter --
-- The Mole: A Measurement of Matter --
• Mass
– Amount of matter an object contains
– SI unit: kilogram (kg)
• Volume
– Space occupied by a sample of matter
– SI derived unit: cubic meter (m3)
• Measurements of matter
– Counting
– Mass or weight
– Volume
• Expressing larger quantities
– Dozen: 12 (used for eggs)
– Gross: 144 (used for pencils)
– Ream: 500 (used for sheets of paper)
– Mole: 6.022 x 1023 representative particles
• Avogadro’s number
– 6.022 x 1023
• Representative particle
– Smallest unit into which a substance can’t be
broken down without a change in composition
Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- The Mole: A Measurement of Matter --
-- The Mole: A Measurement of Matter --
– Can be an atom, ion, molecule, or formula unit
– Most elements, when not bonded with other
elements, exist alone as atoms.
– Diatomic molecules
» Elements that do not exist as single atoms
» Seven diatomic molecules
Seven Diatomic Molecules
(KNOW THESE FOR THE REST OF THE TERM.)
H2
N2
O2
F2
Cl2
Br2
– Molecules
» Nonmetals sharing electrons with nonmetals
» Examples: H2O, CH4
– Formula units
» Generally a metal/cation and a
nonmetal/anion
» Examples: NaCl, MgSO4, (NH4)2CO3
• Working with moles
– Doing calculations with moles involves the use of
conversion factors.
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Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- The Mole: A Measurement of Matter --
-- The Mole: A Measurement of Matter --
– Conversion factors
– Examples
• How many moles of sodium chloride is 2.86 x 1025
formula units of sodium chloride?
– Since formula units are involved, you will use
Avogadro’s number (6.022 x 1023).
– 6.022 x 1023 formula units = 1 mole
• How many molecules of water are in 2.5 moles of
water?
– Since molecules are involved, you will use
Avogadro’s number (6.022 x 1023).
– 6.022 x 1023 formula units = 1 mole
Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- The Mole: A Measurement of Matter --
-- The Mole: A Measurement of Matter --
• How many atoms are in 2.5 moles of water?
– Since atoms are involved, you will use
Avogadro’s number (6.022 x 1023).
– 6.022 x 1023 molecules = 1 mole
– There are 3 atoms in every molecule of water.
• Molar masses
– Gram atomic mass (gam)
• Mass, in grams, of one mole of atoms in a monatomic
element
• Same as average atomic mass for an element from the
periodic table of elements
• Examples
– Gram atomic mass of carbon: 12.011 g/mol
– Gram atomic mass of krypton: 83.80 g/mol
– Gram molecular mass (gmm)
• Mass, in grams, of one mole of a molecular substance
• To find, add up the molar masses of EACH atom in the
chemical formula
Chapter 7: Chemical Quantities
-- The Mole: A Measurement of Matter -• Examples
– H2O: 2(1.0079) + 15.999  18.015 g/mol
– C2H6: 2(12.011) + 6(1.0079)  30.069 g/mol
– Gram formula mass (gfm)
• Mass, in grams, of one mole of an ionic substance
• To find, add up the molar masses of EACH atom in the
chemical formula
• Examples
– NaCl: 1(22.990) + 1(35.453) = 58.443 g/mol
– Mg(NO3)2: 1(24.305) + 2(14.007) + 6(15.999) =
148.313 g/mol
Chapter 7: Chemical Quantities
Mole–Mass and Mole–Volume
Relationships
Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- Mole-Mass and Mole-Volume Relationships --
-- Mole-Mass and Mole-Volume Relationships --
• Molar mass
– Mass of one mole of ANY substance
– More general term than stating gram atomic mass, gram
formula mass, or gram molecular mass
– Does not show what type of compound is being
discussed
– Conversion factors for oxygen gas (O2)
• Molar mass of O2 = 2(15.999) = 31.998 g/mol
• Conversion factor examples
• Conversions among mass, volume, moles, and particles
– Moles will always come up in conversions.
– Always start with what you know.
– Cancel out units to get what you want for units.
– Examples
• Find the number of moles in 93.8 grams of ammonium
phosphate.
– (NH4)3PO4
– Since mass is involved, you will use molar mass.
– Molar mass
» 3 N + 12 H + 1 P + 4 O
» Molar mass = 3(14.007) + 12(1.0079) + 1(30.974)
+ 4(15.999)  149.086 g/mol
Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- Mole-Mass and Mole-Volume Relationships --
-- Mole-Mass and Mole-Volume Relationships --
• Find the mass of 22.8 moles of NaCl.
– Since mass is involved, you will use molar mass.
– Molar mass
» 1 Na + 1 Cl
» Molar mass = 1(22.990) + 1(35.453)  58.443
g/mol
• Find the mass of 2.80  1024 molecules of methane
(CH4).
– Since mass is involved, you will use molar mass.
– Since representative particles are involved, you will
use Avogadro’s number (6.022  1023).
– Molar mass
»1C+4H
» Molar mass = 1(12.011) + 4(1.0079)  16.043
g/mol
Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- Mole-Mass and Mole-Volume Relationships --
-- Mole-Mass and Mole-Volume Relationships --
• Molar volume
– Volume occupied by one mole of a gas at standard
temperature and pressure (STP)
– Molar volume at STP is 22.4 L/mol.
– Standard temperature and pressure
• A condition, NOT a value, of an environment
• Pressure: 1 atmosphere (atm)
• Temperature: 0C
– Measured at STP because of variation in volume among
gases
– Conversion factor examples for oxygen gas (O2) at STP
• Find the volume, at standard temperature and
pressure, of 54.2 grams of argon gas.
– Since mass is involved, you will use molar mass.
– Since volume at STP is involved, you will use molar
volume.
– Molar mass of Ar = 39.948 g/mol
– Molar volume at STP = 22.4 L/mol
Chapter 7: Chemical Quantities
Chapter 7: Chemical Quantities
-- Mole-Mass and Mole-Volume Relationships --
-- Mole-Mass and Mole-Volume Relationships --
• Find the number of atoms in 3.85 grams of propane
gas (C3H8).
– Since mass is involved, you will use molar mass.
– Since representative particles are involved, you will
use Avogadro’s number (6.022  1023).
– Molar mass of C3H8 = 3(12.011) + 8(1.0079)  44.096
g/mol
– 1 molecule of C3H8 = 11 atoms
• Density of a gas
– Density = mass / volume (g/L)
– Density = molar mass / molar volume (at STP)
– Examples
• What is the density of sulfur dioxide gas at standard
temperature and pressure?
– Density = molar mass / molar volume (at STP)
– Molar mass of SO2
»1S+2O
» Molar mass = 1(32.06) + 2(15.999)  64.06 g/mol
– Molar volume at STP = 22.4 L/mol
Chapter 7: Chemical Quantities
-- Mole-Mass and Mole-Volume Relationships -• A gaseous compound composed of sulfur and oxygen
that is linked to the formation of acid rain has a density
of 3.58 g/L at STP. What is the molar mass of this gas?
– Since molar mass is g/mol, you need to cancel out
“L” and replace with “mol”.
– Since, at STP, molar volume relates “L” and “mol”,
molar volume can be used.