The Mole’s Unit NOTES
Name________________________ Period__
The Mole
We cannot see one atom. We cannot see one molecule… they are just too small! So,
Avogadro came up with the idea of “moles”. The number 6.02 x 1023 is called Avogadro’s number.
ONE MOLE OF ANY MATERIAL IS MADE OF 6.02 x 1023 PIECES 1 mole of pencils… 6.02 x
1023 pencils
So if you had one mole of M&M’s that would be equal to 6.02 x 1023 M&M’s!
602,000,000,000,000,000,000,000.0 pieces of anything
If you had a mole of cars, how many would you have? __6.02 x 1023 cars_____
The mole (also abbreviated as mol) is the SI unit of measure for the amount of a substance. The mole
is based on the number of representative particles in 12 g of C-12.
A representative particle is any kind of particle, atoms, molecules, formula units,
electrons or ions.
Molar Mass of an ELEMENT
>The mass in grams of one mole of any pure substance is called its molar mass.
>The molar mass of any element is equal to its atomic mass and has the unit of g/mol.
*Remember, find atomic mass (average atomic mass) by looking elements up on the periodic table!
CLASS EXAMPLES… TO HELP YOU ON THE HOMEWORK:
The atomic mass of Cu is 63.546… The molar mass of Cu is 63.546 g/mol… one mole of Cu = 63.546 g
Gold’s atomic mass is…196.967
Gold’s molar mass is 196.967 g/mol
Zinc’s atomic mass is…_______
Zinc’s molar mass of is ________ g/mol
one mol Au = 196.967 g
one mol Zn = _______ g
Molar Mass of a COMPOUND
To determine the molar mass of a compound, you need to calculate the molar mass of each element is in
the compound, multiply by how many of that element is in the formula, and then add them all together.
The units for molar mass are always g/mol (grams / mole)
*Remember that the molar mass of each element is its atomic mass on the periodic table.
To find mass of each element in the compound
Element 1 =(molar mass) x (# of moles as told by the subscript) = mass in grams
Element 2 =(molar mass) x (# of moles as told by the subscript) = mass in grams
Then you add up all of your answers.
(Element 1 mass in g) + (Element 2 mass in g) = TOTAL Molar Mass for the Compound
Examples: H2O (Water)
Mass of H= (2 moles) x (1.008g) = 2.016g
Mass of O= (1 mole) x (15.999) = 15.999g
TOTAL Molar Mass of H2O = 2.016g + 15.999g =
NOTES PAGE 1
REQUIRED WORK: at least show:
1.008 x 2
+ 15.999 x 1
=
18.015 g/mol
18.015g/mol
Find the molar mass of the following compound:
Calcium Phosphide (Ca3P2)
Mass of Ca= (40.078g) x (3 moles) = 120.234g
Ca+2 P-3
x3 x2
Ca3P2
REQUIRED WORK: at least show:
40.078 x 3
+ 30.974 =
180.382 g/mol
Mass of P =(30.974g) x (2 moles) = 60.148g
TOTAL Molar Mass of Ca3P2= 120.234 + 60.148g = 180.382g/mol
Aluminum Sulfate [Al2(SO4)3]
Al+3 (SO4)-2
X2 x3
Mass of Al = (26.982g) x (2 moles) = 53.964g
Mass of S =(32.066g) x (3 moles) = 96.198g
Al2(SO4)3
Mass of O = (15.999g) x (12 moles) = 191.988g
TOTAL Molar Mass of Al2(SO4)3 = 53.964g + 96.198g + 191.988g = 342.150 g/mol
*Remember, find oxidation numbers of elements when they’re ions then write the formulas
See your Ionic Compounds Unit Homework Packet for how to write formulas!!
THEN you will be able to calculate the molar mass (just like the previous examples).
CLASS EXAMPLES… TO HELP YOU ON THE HOMEWORK:
What is the molar mass of
Beryllium ?
What is the molar mass of
Strontium carbonate ?
One mole of beryllium nitride
what have what mass ?
NOTES PAGE 2
What is the mass of one mole of
Strontium nitrite?
Percent Composition
When we talk about compounds it can be useful to know what elements are in the compound, and
relatively how much of each element there is in the compound.
We talk about “how much” of each element in terms of percentages.
The percent composition then tells what percent of the whole compound is element 1,
what percent of the whole compound is element 2, and what percent of the whole compound is element 3.
If these 3 elements are the ONLY things in the compound, then the percentages should add up to 100%.
To calculate the % Composition:
% composition = (total mass of element/ mass of compound) x 100%
*Find the formula, then find Total mass of the compound before calculating the %composition
Let’s find the % composition of the elements in water H2O :
Mass of H
= 1.008 x 2 moles = 2.016g
1st
Mass of O
= 15.999 x 1 mole = 15.999g
molar
Mass of H2O = 2.016g + 15.999g = 18.015 g/mol of H2O
mass…
Now use the
percent
composition
formula…..
Mass of H =
2.016g
% H = (2.016 /18.015) x 100% = 11.19 % H
Mass of O = 15.999g
% O = (15.999/18.015) x 100% = 88.81% O
Total = 11.19% + 88.81% = 100% water
What is the percent composition of
each element making aluminum oxide?
Class practice
to help you
on the
homework!
NOTES PAGE 3
What is the percent composition of each
element making aluminum cyanide?
Moles to Grams
We are able to convert between number of moles and the mass (in grams) of a substance easily by using
the molar mass of the atom or compound!
We just use dimensional analysis to solve these!
Convert moles of a compound to mass:
Simply multiply the number of moles of the compound by the molar mass of the compound.
For example 0.755 moles of K2CrO4 would be calculated as follows:
2 mol K x 39.10 g/ mol = 78.20 g
Since we have the
formula… find the
molar mass of the
formula first
1 mol Cr x 52.00 g/ mol = 52.00 g
4 mol O x 16.00 g/ mol = 64.00 g
Molar mass K2CrO4 = 194.20 g/mol
Grams means mass right?!
SO, “Molar mass“ goes on “grams”…
NOW the
conversion….
0.755 mols of K2CrO4 x 194.20 g = 145.621
1
1 mole
with 3 sig.figs
or 146 g
A “mole” is bigger than a gram. Always put “1”
on moles UNLESS the “moles is the given.
CLASS EXAMPLES… TO HELP YOU ON THE HOMEWORK:
1.50 mol Potassium
= _________ g
0.750 mol Aluminum
= __________ g
3.850 mol Lithium phosphide
= __________ g
3.850 mol Lithium carbonate
= ___________ g
SUMMARY of how to set up & solve
mole conversions on the back page!
NOTES PAGE 4
Grams to Moles Going from mass to moles is the same process in reverse!
It is still just dimensional analysis.
For example 150 grams of K2CrO4 would be calculated as follows:
Molar mass K2CrO4 = 194.20 g/mol
First… find the formula &
molar mass of the formula
NOW the
conversion….
keep 2 sig figs..
150 g of K2CrO4 x 1 mole = 0.7723 rounds to.. 0.77 g
1
194.20 g
Grams to Moles Examples to help you on the homework!
148 g Argon
= _________ mol
78.3 g Rubidium oxide
= ___________ mol
65.7 g Titanium
= ___________ mol
75.3 g radium chloride
= __________ mol
SUMMARY of how to set up & solve
mole conversions on the back page!
WHAT ARE PARTICLES ?
1 mole is made of 6.02 x 1023 particles of any one thing.
**Particle is generic way of saying atom,
formula units, or molecule
Which particle is used and how to know when:
Atom: the smallest particle if the material is one pure element
(Ex. Al , Cu, C, Ne…1 element)
Molecule: the smallest particle of a covalent compounds (two or more nonmetals bonded)
Ex. CO2
Formula Unit: the smallest particle of an ionic compound (metal bonded with a nonmetal) Ex. NaCl
If you had 2 dozen eggs… wouldn’t you say 2 x 12 = 24 eggs.
NOTES PAGE 5
2 dozen
1
12 eggs = 24 eggs
1 dozen
A dozen is a number. Well, a “mole” is a number too…. a really, really BIG number.
Moles to Particles Calculations
If you have 1 mole of Copper you have = 6.02 x 1023 atoms of Cu
If you have 1.75 moles of Copper you have = _?___ atoms of Cu
We need a HUGE amount of particles (like atoms) to make 1 mole…
…6.02 x 1023 particles here
1.75 moles x (6.02 x 1023 atoms ) = (1.05 x 1024) atoms of Cu
1 mole
A “mole” is bigger than any particle. Always put “1” on moles
UNLESS the “moles is the given.
TIPS: Write the units…. THEN put in the numbers. Moles is always “1” unless it’s given.
Number of “particles (any type)” is always 6.02 x 1023.
It’s easy with dimensional Analysis!
Moles to Particles EXAMPLES…
3.25 mol AgNO3
= __________________ formula units AgNO3
11.5 mol H2O
= __________________ molecules H2O
0.4 mol of Au
= ___________________ atoms Au
Particles to Moles Calculations :
If you have 6.02 x 1023 atoms of Lithium you have = 1 mol Li
EX. If you have 2.04x 1024 formula units of Lithium fluoride you have = ? mol LiF
A “mole” is bigger than any particle. Always put “1” on
moles UNLESS the “moles is the given.
2.04x 1024 formula units x (__1 mole__
6.02 x 1023
) = (1.05 x 1024) atoms of Cu
formula units
We need a HUGE amount of particles (like formula units) to
make 1 mole……6.02 x 1023 particles here
Particles to Moles Examples:
2.58 x 1024 atoms of Calcium
= __________ mol Ca
3.6 x 1023 molecules of CH4
= _________ mol CH4
SUMMARY of how to set up & solve
NOTES PAGE 6
mole conversions on the back page!
2.04 x 1022 formula units of KBr
= __________ mol KBr
Grams to Particles
We are able to go directly from mass (in grams) to number of particles (atoms, formula units, or
molecules) by using Avogadro’s number and the molar mass.
EX. If you have 35.7 grams of Lithium fluoride you have = ? mol LiF
We need a HUGE amount of particles (like formula units) to
make 1 mole……6.02 x 1023 particles here
35.7 grams x (__6.02 x 1023 formula units
25.939 grams LiF
Li F
6.941 + 18.998 =25.939 g/mol
) = 8.29 x 1023 formula units of LiF
“grams” reminds us to write the “molar mass” using the
atomic masses from the periodic table as the formula says to.
Grams to Particles Examples:
29 g Helium
= ___________ atoms He
36.08 g CO2
(44.009 g is molar mass)
= __________ molecules CO2
0.50 g ZnS
(97.386 is molar mass)
= ________ formula units ZnS
Particles to Grams
Going from particles to mass is the same process in reverse!
3.76 x 1023 formula units of LiF
x (__25.939 grams LiF
) = 35.7 grams
23
6.02 x 10 formula units
See how grams reminds of molar mass and where it belongs this
time…. And Avogadro’s number goes on the particles here.
Particles to Grams Examples:
1.98 x 1023 atoms Titanium
= ________ g Ti
8.500 x 1023 atoms Xe
= _______ g Xe
1.187 x 1024 molecules Cl2
= ________ g Cl2
NOTES PAGE 7
SUMMARY of MOLE CONVERSIONS: HOW TO SET UP & SOLVE any of them
You must write the units
# GIVEN UNIT _____MULTIPLY BY:_ ∎ What you’re “LOOKING FOR”
1
DIVIDE BY: ∎ (copy the GIVEN UNIT here)
∎ What number do I use there?
∎ IF this position says “grams”---write the molar mass with it (use atomic masses…)
∎ IF this position says “moles” WRITE “1” always!
∎ IF this position is particle “atoms, molecules, formula units” WRITE “6.02 x 1023” always!
Name the types of elements:
A) Group 1: _______________
B) Group 2
_______________
C) Groups 3 to 12: _______________
E) C, N, O, F, P, S, Cl, Se, Br, I = __________
F) Group 17 = ______________
G) Group 18 = ______________
D) B, Si, Ge, As, Sb, Te, Po = __________
H) Write the oxidation numbers for groups on this periodic table:
I) Draw a line “down” through symbols that do NOT need roman numerals.
NOTES PAGE 8