Day 1:
Moles
Molar Mass
What Are Some Typical Counting Numbers?
1 dozen eggs is how many eggs?
1 gross of pencils is how many pencils?
1 ream of paper is how many papers?
1 pair of socks is how many socks?
What is a Mole?
A mole is an amount or counting number
used in chemistry.
It is a BBBBIIIIIIGGGGGG number!
It helps us count things that are really small
(like atoms or molecules).
Video Clip
• https://www.youtube.com/watch?v=TEl4jeET
Vmg
• 1 mole = 6.02 x 1023 particles
• 1 mol of hockey pucks would equal
the weight of the moon!
• 1 mol of basketballs would fill a bag
the size of Earth
• 1 mol of soda cans would cover the
Earth’s surface 200 miles deep
The Chemist’s Counting Unit
• Reams, gross, pairs and dozens do not help
the chemist.
• What does? Something that allows you to
count something really small like atoms.
• The MOLE unit!!! A mole is 6.02 x 1023 of
something, like atoms or molecules.
Molar Mass
Molar Mass: the sum of all the atomic masses
of the elements in the compound or molecule
1 mole = MOLAR MASS of compound/element
Units for Molar Mass are g/mol
Demo
Practice
Find the Molar Mass for sodium chloride.
Formula: ________________
Na
Cl
Molar mass = ____________
Steps to Solve for Molar Mass
1) Write the formula for the compound
2) List all the elements in the compound
3) Write how many of each element is in the
compound
4) Write the average atomic mass of each
element from the periodic table
5) Multiply average atomic mass by how many
atoms are in the compound
6) Add all totals to get the total Molar Mass
7) Don’t forget the units!!! (grams/mole)
Practice
• Ba(NO3)2
• CuCl2
Practice
• N2O5
• CaN2
Practice
• Na2SO4
• MgS
Molar Mass
• Mass of 1 mole of an element or
compound.
• Atomic mass tells the...
– atomic mass units per atom (amu)
– grams per mole (g/mol)
• Round to 2 decimal places
Molar Mass Examples
• carbon
12.01 g/mol
• aluminum
26.98 g/mol
• zinc
65.39 g/mol
Molar Mass Examples
• water
 H2O
 2(1.01) + 16.00 = 18.02 g/mol
• sodium chloride
 NaCl
 22.99 + 35.45 = 58.44 g/mol
Demo
• Weigh 1 mole of water and
compare
• Weight 1 mole of NaCl (salt) and
compare
% Composition
A pure compound always consists of the same
elements combined in the same proportions by
weight.
Therefore, we can express molecular
composition as PERCENT BY WEIGHT.
MgCl2
25.53% Mg
74.46% Cl
How To Calculate % Composition
Examples and Practice from
Homework
Bell Work Problem:
Percent Composition
What is the percent carbon in C5H8NO4 (the
glutamic acid used to make MSG monosodium
glutamate), a compound used to flavor foods and
tenderize meats?
a) 8.22 %C
b) 24.3 %C
c) 41.1 %C
Empirical Formulas
And
Molecular Formulas
Timberlake LecturePLUS
21
Types of Formulas
The formulas for compounds can be expressed as an
empirical formula and as a molecular(true) formula.
Empirical
Molecular (true)
CH
C2H2
CH
C6H6
CO2
CO2
CH2O
C5H10O5
Timberlake LecturePLUS
22
Empirical Formulas
Write your own one-sentence definition for each of
the following:
Empirical formula
Molecular formula
Timberlake LecturePLUS
23
• An empirical formula represents the simplest
whole number ratio of the atoms in a
compound.
• The molecular formula is the true or actual
ratio of the atoms in a compound.
Timberlake LecturePLUS
24
Learning Check
A. What is the empirical formula for C4H8?
1) C2H4
2) CH2
3) CH
B. What is the empirical formula for C8H14?
1) C4H7
2) C6H12
3) C8H14
C. What is a molecular formula for CH2O?
1) CH2O
2) C2H4O2
Timberlake LecturePLUS
3) C3H6O3
25
Solution
A. What is the empirical formula for C4H8?
2) CH2
B. What is the empirical formula for C8H14?
1) C4H7
C. What is a molecular formula for CH2O?
1) CH2O
2) C2H4O2
Timberlake LecturePLUS
3) C3H6O3
26
Learning Check
If the molecular formula has 4 atoms of N,
what is the molecular formula if SN is the
empirical formula? Explain.
1) SN
2) SN4
3) S4N4
Timberlake LecturePLUS
27
Solution EF-2
If the molecular formula has 4 atoms of N,
what is the molecular formula if SN is the
empirical formula? Explain.
3) S4N4
If the actual formula has 4 atoms of N, and S is
related 1:1, then there must also be 4 atoms of
S.
Timberlake LecturePLUS
28
Stoichiometry Worksheet #3
• Complete questions 1-12 at this
time.
• Ask questions if you need
help!!!
How To Create Empirical Formula from
Molecular Formula and Vice Versa
C. Molar Conversion Examples
• How many moles of carbon are in
26 g of carbon?
26 g C 1 mol C
12.01 g C
= 2.2 mol C
C. Molar Conversion Examples
• How many molecules are in 2.50
moles of C12H22O11?
6.02  1023
2.50 mol molecules
1 mol
= 1.51  1024
molecules
C12H22O11
Examples from the Homework
(Stoichiometry Worksheet #4)