Transcript The Mole

The Mole
Chemistry’s Unit of Convenience
Calling particles by the right name
Particles of a type of a(n)…
 ion……………………
 element………………..
 diatomic compounds….
 covalent compound……
 ionic compound……….
are called…
ions
atoms
molecules
molecules
formula units
(f.u.)
Revisiting Chemical Reactions

A typical synthesis reaction:
2 Mg + O2  2 MgO

now balance it…
•What does this mean?
* Two _____
atoms of Mg react with one ________
molecule
of O2 to produce two ___________
formula units of MgO
Ratios in Chemical reactions
The chemicals involved in this reaction some
together in a specific ratio:
2 Mg + O2  2 MgO
2 : 1 :
2
The ratio comes from the coefficients.
What if I “doubled” the “recipe”--what would
the equation mean then?
4 atoms : 2 molecule : 4 formula units
Those are not convenient amounts!
Atoms are so small that it is hard to work
with chemical equations on the atomic scale.
 If I did the recipe 12 times over,
then the ratio would be from 2 : 1 : 2 to

24 atoms : 12 molecules : 24 f.u.

Simplifying in “dozens:”
2 doz atoms : 1 doz molec : 2 doz f.u.
Convenient units… like dozen
“Dozen” is convenient because we all know
that “one doz = 12” of whatever…
 In chemistry we have a convenient unit
called the MOLE.

1 mol = 6.02 x 1023 particles
• In other words:
1 mol = 602000000000000000000000
Mole Facts
One mole of rice grains is more than all the
rice that has been grown since the beginning
of time!
 One mole of hockey pucks would be equal
in mass to the mass of the moon!
 Assuming the human body has 60 trillion
cells (6 X1013) and there are 6 billion people
(6 X109) on earth, the total number of human
cells on earth is about ½ a mole!

Things to know:
The mole is a constant number.
 The number for the mole is also called
Avogadro’s number.
 Factoring comes in handy when dealing
with the mole!
 Conversion factors:

Practice (using factoring!):
How many atoms are in 5 moles of Lithium?
 How many molecules are in 4.5 moles of chlorine gas?
 How many f.u. are in 6 mol of potassium chloride?
 How many moles are there in 5.66 X1023 atoms of
neon?
 How many moles are there in 2.888 X1015 formula units
of sodium iodide?
 How many moles are there in 4.6 X1045 molecules of
carbon tetrachloride?

Back to the Equation:
2 Mg + O2  2 MgO
This can be interpreted several ways--
2 atoms Mg : 1 molec O2 : 2 f.u. MgO
2 doz of atoms Mg : 1 doz of molec O2 :
2 doz of f.u. MgO
2 mol of atoms Mg : 1 mol of molec O2 :
2 mol of f.u. MgO
MOST SIMPLY PUT:
2 mol Mg : 1 mol O2 : 2 mol MgO
More examples:
2 H2 + O2  2 H2O
6 CO2 + 6 H2O  C6H12O6 + 6 O2
CH4 + 2 O2  CO2 + 2 H2O
H2 + Cl2  2HCl
How is this helpful?

The mole is connected to the Periodic Table!
“The mass of one mole of atoms of a pure
element in grams is numerically equal to the
atomic weight of that element in amu. This is also
called the “molar mass.” The SI unit is g/ mol.

We already know the molar mass of
EVERYTHING in Chemistry!
Atomic mass: amu :: molar mass : grams
How is this helpful?
 Atomic
mass of Mg:
24 amu
 Therefore, the molar mass Mg:
I
24 g
can’t say, “go get 2 atoms of Mg…”
I CAN say, “go get 2 mol Mg”
because I know that 1 mol of Mg = 24 g Mg
But
More practice with molar mass:

Find the molar mass of the following:
63.5 g/mol
Cu =
Au = 197.0 g/mol
Pb = 207.2 g/mol
He = 4.0 g/mol
Ca =
Na =
C=
Xe =
40.1 g/mol
23.0 g/mol
12.0 g/mol
131.3 g/mol
Those were all elements...
 If
I have one mol oxygen gas, how
can I know the molar mass?
 Oxygen
 One
gas = O2
[remember diatomic!]
mol O2 = two mol O atoms
 molar
mass O = 16 g
 molar mass O2 = 2(16g) = 32.0 g
Molar Mass of Molecules

Find the molar mass of these molecules:
CO =
28.0 g/mol
32.0 g/mol
CO2 =
44.0 g/mol
N2 = 28.0 g/mol
CH4 =
16.0 g/mol
Cl2 =
NH3 =
17.0 g/mol
H2=
2.0 g/mol
O2 =
71.0 g/mol
Try these chemical compounds:
CaCl2
= [one mol Ca + two mol Cl]
1(40.1 g) + 2(35.5 g) = 111.1 g
 Al2(SO4)3 =
2 (27.0 g Al) + 3 (32.1 g S) + 12 ( 16.0 g O) =
54.0 g + 96.3 g + 192.0 g = 342.3 g/mol
For an extra challenge:
 “TNT”
[C7H5(NO2)3]
• 7 (12 g C) = 84.0 g
• 5 (1.0 g H) =
5.0 g
•3 (14.0 g N) = 42.0 g
•6 (16.0 g O) = 96.0 g
227.0 g; TNT is 227 g/mol
Molar mass as a conversion factor
The molar mass is a connection between g and mol
What is the mass in grams of 3.5 mol of copper?
 What is the mass in grams of 7 moles of PbSO4?
 How many moles are there in 38 g of Mg?
 How many moles are there in 339 g of KCl?

Another mole conversion factor
•
1 mol of a gas = 22.4 L @ STP
• STP = Standard Temperature and Pressure
Now you can convert moles into particles,
grams, and liters.
•
•
•
How many moles are in 47 L of hydrogen gas at
STP?
If I have 4.5 moles of oxygen gas at STP, how
many Liters do I have?
How many moles are in 100 L of methane?
Percent composition
Calculate the formula (or molar) mass
 Calculate the formula mass for the element or
elements in question
 Divide the total mass of EACH element by the
formula mass of the compound and multiply
times 100.
Examples: Find the percent comp for--Al2O3
-HgO
-Fe2O3
-H2SO4

Mole Road Map
Particles
Grams
MOLES
Liters