Unit 8
Chemical Quantities
Chemistry I
Mr. Patel
SWHS
Topic Outline
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MUST have a scientific calculator (not graphing)!!!
Review of Factor-label Method
The Mole: Particle to Mole Conversion (10.1)
Molar Mass: Gram to Mole Conversion (10.2)
Molar Volume: Volume to Mole Conversion (10.2)
Chemical Formula as a Conversion Factor (N/A)
Percent Composition (10.3)
Empirical and Molecular Formulas (10.3)
Solution Concentration (16.2)
PART I:
CHEMICAL
CONVERSIONS
Conversion Factors
• Conversion factor – allows us to convert from
one unit to another unit
– Example: 1m = 1000mm, 1 dozen = 12 items
• We use the factor label method to convert
Given
New Unit
=
Old Unit
Desired
Quantity
Remember:
Multiply the top
Divide the bottom
Measuring by Count
• A count refers to a grouping or a word
representing a number
– Pair (2), Dozen (12), Ream (500)
• A count is a conversion factor – can convert
between a count unit and the number of
items
– Ex: 1 dozen egg is the same as 12 actual eggs
Ex: Convert 3 dozen apples to number of apples.
Use the factor-label method.
3 dozen apples
12
1
apples
dozen apples
=
36 apples
Representative Particle
• Representative Particle – species present in a
substance
– Atoms (elements; ex: Fe atom)
– Molecules (covalent compounds; ex: diatomics)
– Ions (species with a charge; ex: Na1+)
– Formula Units (ionic compounds; ex: NaCl)
The Mole
• The fundamental count in chemistry is the
mole – SI unit for amount
– Very similar to a dozen; represents a number
– Abbreviation: mol
– Contains an Avogadro’s Number of items
– Avogadro’s Number = 6.02 x 1023 (memorize this!)
Conversion Factor 1: 1 mole = 6.02 x 1023 items
The Mole
• It is not appropriate to consider only one atom
of an element or one formula unit of a
compound
– It is easier to group atoms using a large number
– NOTE: 1 mole contains the same number of
item…but does not necessarily have the same
mass!!!
The Mole
• Just like a dozen, the mole is a conversion
factor!
• We can convert between the unit (mole) and
the number of items
• Remember:
– 1 mole X = 6.02 x 1023 X
– You can substitute any item for the X
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units)
Ex: Convert 1 mole of Fe to number of Fe atoms.
Use the factor-label method.
1 mol Fe
6.02 x 1023 atoms Fe
= 6.02 x 1023 atoms Fe
1
mol Fe
Math: (1) x (6.02 x 1023) / (1) = 6.02 x 1023
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 7.8 mol of clipped fingernails to
number of clipped fingernails (CF).
Use the factor-label method.
7.8 mol CF
6.02 x 1023
CF
=
1
4.7 x 1024 CF
mol CF
Math: (7.8) x (6.02 x 1023) / (1) = 4.7 x 1024
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 2.1 x 109 atoms of Li to moles of Li.
Use the factor-label method.
2.1 x 109 atom Li
1
mol Li
=
3.49 x 10-15 mol Li
6.02 x 1023 atoms Li
Math: (2.1 x 109) x (1) / (6.02 x 1023) = 3.49 x 10-15
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Try the following conversions.
1) 1.75 molecules CHCl3
to mol CHCl3
1) 2.91 x 10-24 mol CHCl3
2) 1.7 x 1015 mol of H+
to ions H+
2) 1.0 x 1039 ions H+
3) 2.80 x 1024 atoms Si
to mol Si
3) 4.65 mol Si
Mass of an Element
• On the periodic table, the mass of an element
is given in units of atomic mass unit
– 1/12 the mass of a carbon-12 atom
• In the laboratory, we do not use amu. We
measure chemicals in grams.
• We can treat the amu as “grams per mole”.
– Carbon: 12 amu  12 grams in 1 mole
Mole-Atom-Mass Relationship
Element
Moles
# of Atoms
Mass
Molar Mass
Al
1 mol
6.02 x 1023
26.98g
26.98 g/mol
N
1 mol
6.02 x 1023
14.01g
14.01 g/mol
Pb
1 mol
6.02 x 1023
207.2g
207.2 g/mol
S
1 mol
6.02 x 1023
32.07g
32.07 g/mol
Molar Mass (MM)
• The mass of one mole of an element of
compound
– Units: grams/mole (g/mol)
– Can be called Molecular Weight (MW)
– For element, MM comes directly from mass on PT
– For compound, add the mass of each atom
• CO2 = Add (mass of C) and 2 x (mass of O)
Conversion Factor 2: 1 mole = Mass in Grams (from PT)
Ex: What is the molar mass of iron?
55.85 g/mol Fe (from Periodic Table)
Ex: What is the molar mass of boron?
10.81 g/mol B (from Periodic Table)
Ex: What is the molar mass of H2O?
H: 2 x 1.01g = 2.02g
O: 1 x 16.00g = 16.00g
18.02 g/mol H2O
Ex: What is the molar mass of C6H12O6?
C: 6 x 12.01g = 72.06g
H: 12 x 1.01g = 12.12g
O: 6 x 16.00g = 96.00g
180.18 g/mol C6H12O6
Molar Mass Conversions
• The molar mass is a conversion between the
mole and grams.
– Moles are used in theory
– Grams are used in lab/practice
• Molar Mass allows:
mole  grams
• Using 2 conversion factors: particle  grams
– We must go through the mole!!!
GRAMS
1 mole
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 2.00 mol Carbon to grams C.
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol C = 12.01 g C
2.0 mol C
12.01 g C
=
1
24.02 g C
mol C
GRAMS
1 mole
Math: (2.0) x (12.01) / (1) = 24.02
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 9.73 mol Fe to grams Fe.
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol Fe = 55.85 g Fe
9.73 mol Fe
55.85 g Fe
=
1
543 g Fe
mol Fe
GRAMS
1 mole
Math: (9.73) x (55.85) / (1) = 543
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 122 g Al to moles Al.
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol Al = 26.98 g Al
122 g Al
1 mol Al
= 4.52 mol Al
26.98 g Al
GRAMS
1 mole
Math: (122) x (1) / (26.98) = 4.52
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 413 g C6H12O6 to moles C6H12O6.
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol C6H12O6 = 180.18 g C6H12O6
413 g C6H12O6
1 mol C6H12O6
= 2.29 mol C6H12O6
180.18 g C6H12O6
GRAMS
1 mole
Math: (413) x (1) / (180.18) = 2.29
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 26 g He to atoms He.
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol He = 4.00 g He
26 g He
This is Avogadro’s Number
1 mol = 6.02 x 1023 atoms
1 mol He 6.02 x 1023 atom He
= 3.9 x 1024 atom He
4.00 g He
1
mol He
GRAMS
Math: (26) x (1) / (4.00) x (6.02 x 1023) / (1)
= 3.9 x 1024
1 mole
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Ex: Convert 345 g CO2 to molecule CO2.
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol CO2 = 44.01 g CO2
345 g CO2
This is Avogadro’s Number
1 mol = 6.02 x 1023 atoms
1 mol CO2 6.02 x
44.01 g CO2
1
1023
molec
CO2
mol CO2
=
4.72 x 1024
molecules CO2
GRAMS
Math: (345) x (1) / (44.01) x (6.02 x 1023) / (1)
= 4.72 x 1024
1 mole
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Try the following.
1) What is the Molar Mass
of Platinum (Pt)?
1) 195 g/mol
2) Convert: 652.7 g H2O
to molecules H2O
2) 2.18 x 1025 molec. H2O
GRAMS
1 mole
MM=P.T.
MOLES
1 mole
6.02x1023
PARTICLES
(atoms, molecules,
ions, formula units )
Mole to Volume Conversion
• Gases are often measured in volume rather
than grams
• A conversion is available between mole and
volume only at specific conditions
– Only for gases (ideal)
– Standard Temperature and Pressure (STP)
– 0oC and 1 atm
Conversion Factor 5: 1 mole = 22.4 L
LITERS
1 mole
Molar
Volume
MOLES
1 mole
1 mole
Avogadro
Number
Molar Mass
GRAMS
PARTICLES
(atoms, molecules,
ions, formula units)
Ex: Convert 5 mol N2 to liters of N2.
Use the factor-label method.
5 mol N2
22.4 L N2
1
mol N2
Math: (5) x (22.4) / (1) = 122
=
112 L N2
Ex: Convert 12.5 mol Ar to liters of Ar.
Use the factor-label method.
12.5 mol Ar
22.4 L Ar
=
1
mol Ar
Math: (12.5) x (22.4) / (1) = 280
280 L Ar
Ex: Convert 69.8 L Ne to mol of Ne.
Use the factor-label method.
69.8 L Ne
1
mol Ne
= 3.17 mol Ne
22.4
L Ne
Math: (69.8) x (1) / (22.4) = 3.17
Ex: Convert 49.87 g NH3 to liters NH3 at STP.
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol NH3 = 17.04 g NH3
49.87 g NH3
1 mol NH3
17.04 g NH3
This is Molar Volume at STP
1 mol = 22.4 L
22.4 L NH3
1 mol NH3
Math: (49.87) x (1) / (17.04) x (22.4) / (1)
= 65.56
=
65.56 L NH3
Try the following.
1) What is the volume (L)
of 589 g N2O?
1) 300. L
2) Convert: 3.01 x 1023
molecules of SO2 to
liters.
2) 11.2 L H2O
Chemical Formula
• The chemical formula can act as a conversion
• Example: Fe2O3
– The subscripts tell us the number of atoms
– 2 atoms of Fe and 3 atoms of O in one formula
unit of Fe2O3
– Assume we have 6.02 x 1023 formula units then…
– Fe: 2 x (6.02 x 1023 atom Fe) = 2 mole Fe
in 1 mol
Fe2O3
– O: 3 x (6.02 x 1023 atom O) = 3 mole O
Chemical Formula
• The chemical formula is a mole ratio!!!
• If we have 1 mole C6H12O6 then…
1 mol C6H12O6 : 6 mol C : 12 mol H : 6 mol O
Colon (:) means chemically equivalent
Conversion Factor 3: Chemical Formula (mole to mole)
Chemical Formula
Conversion Factor 3: Chemical Formula (mole to mole)
• NOTE!!! When you are changing from one
chemical to another, you must do this through
the mole stage!
– Mole X  Mole Y
• This is strictly a mole to mole conversion.
– NOT GRAMS!!!
Chemical
Formula
LITERS
1 mole
22.4 L
MOLES
1 mole
1 mole
6.02x1023
Molar Mass
Periodic Table
GRAMS
PARTICLES
Ex: How many mol of N are in 1.00 mol NO3?
Use the factor-label method.
This is Mole ratio
from chemical formula
1 mol NO3 = 1 mol N
1.00 mol NO3
1
mol N
=
1 mol NO3
Math: (1.00) x (1) / (1) = 2.00
1.00 mol N
Ex: How many mol of P are in 1.00 mol P2O5?
Use the factor-label method.
This is Mole Ratio
from chemical formula
1 mol P2O5 = 2 mol P
1.00 mol P2O5
2
mol P
=
1 mol P2O5
Math: (1.00) x (2) / (1) = 2.00
2.00 mol P
Ex: How many mol of S are in 6.80 mol Pb2S3?
Use the factor-label method.
This is Mole Ratio
from chemical formula
1 mol Pb2S3 = 3 mol S
6.80 mol Pb2S3
3
mol S
=
1 mol Pb2S3
Math: (1.00) x (2) / (1) = 2.00
20.4 mol S
Ex: How many grams of Cl are in 8.00 mol CHCl3?
Use the factor-label method.
This is Mole Ratio
from chemical formula
1 mol CHCl3 = 3 mol Cl
8.00 mol CHCl3
This is Molar Mass
from periodic table
1 mol Cl = 35.45 g Cl
3
mol Cl
35.45
g Cl
=
1 mol CHCl3
1
mol Cl
Math: (8.00) x (3) / (1) x (35.45) / (1) = 851
851 g Cl
Ex: How many grams of O are in 15 mol NO2?
Use the factor-label method.
This is Mole Ratio
from chemical formula
1 mol NO2 = 2 mol O
15 mol NO2
This is Molar Mass
from periodic table
1 mol O = 16.00 g CO2
2
mol O
16.00
gO
=
1 mol NO2
1
mol O
Math: (15) x (2) / (1) x (16.00) / (1) = 480
480 g O
Ex: How many grams of F are in 10.2 g XeF6?
Use the factor-label method.
This is Molar Mass
from periodic table
1 mol XeF6 = 245.29 g XeF6
10.2 g XeF6
1
This is Mole Ratio
from chemical formula
1 mol XeF6 = 6 mol F
mol XeF6 6
245.29 g XeF6
mol F
This is Molar Mass
from periodic table
1 mol F = 19.00 g F
19.00 g F
1 mol XeF6 1 mol F
Math: (10.2) x (1) / (245.29) x (6) / (1) x (19.00) / (1)
= 4.74
=
4.74 g F
Try the following.
1) How many moles of
acetate are in 2.00 mol
Cr(C2H3O2)3?
1) 6 mol C2H3O21-
2) Convert: 121 g NaOH
to grams H.
2) 3.03 g H
PART II:
PERCENT
COMPOSITION
Percent Composition
• Describes the relative amounts of each
element in a compound
• The percent composition is always the same no matter the quantity of the sample
• Also called “Percent by Mass”
%X=
mass of X
mass of sample
x 100%
(X represents some element found in the sample)
Ex: When 13.60 g sample of MgO decomposes, it
produces 8.20 g Mg and 5.40 g O.
What is the % composition?
% Mg =
mass of Mg
mass of MgO
x 100% =
8.20 g Mg
13.60 g MgO
x 100%
% Mg = 60.3% Mg
%O =
mass of O
mass of MgO
x 100% =
5.40 g O
13.60 g MgO
% O = 39.7% O
Note: All percents should add up to about 100%
x 100%
Ex: When 89.1 g H2O decomposes, it produces
9.89 g H.What is the % composition?
%H =
mass of H
mass of H2O
x 100% =
9.89 g H
89.1 g H2O
x 100%
% H = 11.1% H
%O =
mass of O
mass of H2O
x 100% =
(13.60 – 9.89) g O
13.60 g H2O
x 100%
% O = 88.9% O
Total mass must equal the sum of its parts: mass H2O = mass H + mass O
Ex: What is the % composition of C3H8?
If we assume 1.00 mol of sample, then we can use periodic table for the mass!!!
• Mass of C:
3 mol x 12.01 g/mol = 36.03 g C
• Mass of H:
8 mol
• Mass of C3H8:
44.11 g/mol C3H8
%C =
%H =
36.03 g C
44.11 g C3H8
8.08 g H
44.11 g C3H8
x 1.01 g/mol
= 8.08 g H
x 100% = 81.68% C
x 100% = 18.32% H
Ex: What is the % composition of (NH4)2S?
If we assume 1.00 mol of sample, then we can use periodic table for the mass!!!
• Mass of N:
2 mol x 14.01 g/mol = 28.02 g N
• Mass of H:
8 mol
x 1.01 g/mol
• Mass of S:
1 mol
x 32.07 g/mol = 32.07 g S
• Mass of (NH4)2S:
%N =
%H =
%S =
= 8.08 g H
68.17 g/mol (NH4)2S
28.02 g N
68.17 g (NH4)2S
8.08 g H
68.17 g (NH4)2S
32.07 g S
68.17 g (NH4)2S
x 100% = 41.10% N
x 100% = 11.85% H
x 100% = 47.04% S
Try the following.
1) What is the percent
composition of NaOH?
1) 57.5% Na
40.0% O
2.5% H
2) What is the percent
composition of CH4?
2) 75.0% C
25.0% H
PART III:
EMPIRICAL & MOLECULAR
FORMULAS
Empirical and Molecular Formulas
• Each compound has a basic ratio of elements
• C6H6 , C8H8 , C10H10  multiples of CH
• Empirical Formula (EF)
– Lowest whole number ratio of elements
– Ex: CH, CH2O
• Molecular Formula (MF)
– Actual ratio of elements in a compound
– Can be the same or whole # multiple of empirical
– Ex: C6H6, C6H12O6
Empirical and Molecular Formulas
• To determine the empirical, you need % comp
– Assume 100g of compound to make math easier
• To determine the molecular, you need
1. Molar Mass of Compound (Mass Spec)
2. Calculate the Ratio of MF to EF
Ratio
=
Molecular Molar Mass
Empirical Molar Mass
Molecular Molar Mass is given in the problem.
Step to Solve EF/MF Problems
Ex: A molecule was determined to be 30.4% N and
69.6% O with a molar mass of 92.02 g/mol.
Determine the empirical & molecular formulas.
Ex: 40.0% C, 6.67% H, 53.3% O; MM=90.00 g/mol.
Determine the empirical & molecular formulas.
Ex: A 150g sample consists of 74.25g C, 7.725g H,
43.35g N, and 24.75g O - molar mass of 195 g/mol.
Determine the empirical and molecular formulas.
Answer:
Empirical: C4H5N2O
Molecular: C8H10N4O2
Try the following.
1) Find the EF & MF for:
75.69 % C, 8.80% H,
15.51% O
with MM = 206 g/mol
1) EF: C13H18O2
MF: C13H18O2
(Ibuprofen)