The Mole
What's a mole?
In chemistry, a mole is a counting unit.
What does that mean?
– 1 dozen = 12 units(ie eggs,donuts)
– 1 mole = 6.02x1023 particles.
– That's 602,000,000,000,000,000,000,000 particles!
– 6.02x1023 is Avogadro's Number
A mole is used to represent lots of particles
– atoms
– molecules(covalent compounds)
– ions
– Forumula Units (ionic compounds)
The Mole
If you have 3 particles of water, what do you have?
You have 3 water molecules because H2O is molecular
Covalently bonded compounds are called molecules
If you have 4 particles of table salt, what do you have?
You have 4 NaCl formula units becauseNaCl is ionic
Ionic compounds are called formula units
If you have 5 particles of gold, what do you have?
You have 5 gold atoms because gold is an element
Atoms are the unit for elements
The Mole
How do you represent 6.02x1023 in a scientific calculator?
You can type 6.02x10^23 if you want...
but there's a better way!
-
For graphing calculators:
Type in 6.02 then the 2nd button, then the “,” button, then 23
The calculator will display 6.02E23
This means “6.02x1023” to the calculator.
- For other calculators there is usually a key marked “E”
or “EXP” that allows you to enter numbers in scientific
notation.
How BIG is Avagadro's Number?
➔6.02x1023 dollars would be enough to give every person
on Earth $87 trillion. That’s $1 million a second for the
next 2.8 years.
➔A modern computer that can make up to 100 million
counts per second would take almost 200 million years
to count to 6.02x1023
➔If 6.02x1023 snowflakes fell evenly across the United
States, the blanket of snow would cover every building
in the country, including the tallest skyscrapers.
➔If you could travel at the speed of light (186,000 mi/s in
a vacuum), it would take you more than 100 billion years
(longer than the Universe has been around) to travel
6.02x1023 miles.
Moles & Particles
o If 1 mole = 6.02 x 1023, then we can determine how many
atoms(or molecules) are in stuff.
o 1 mole : 6.02 x 1023
Or
1 mol
6.02 x 1023 particles
o How many silver atoms are in 3 moles of Ag?
(using dimensional analysis (factor method))
3 mol Ag x 6.02 x 1023 atoms Ag =
1mol Ag
Waitaminute… but why are moles on the bottom and Avogadro’s
number on the top?
Since 1mol = 6.02x1023, either one can be on top, we just choose
the one that will cancel out the original unit.
Mole to Particle Conversions
Examples:
How many molecules of methane are in 4.50 mol of methane?
4.50 mol CH4 x
6.02x1023 molecules CH4
1 mol CH4
= 2.71x1024 molecules CH4
How many moles of iron are in 2.39x1024 iron atoms?
1 mol Fe = 6.02x1023 Fe atoms
2.39x1024 atoms Fe
x
1 mol Fe
6.02x1023 atoms Fe
= 3.97 mol Fe
Molar Mass
•
•
•
•
•
•
Atomic measures the mass of atoms
• Really small!
Atomic Mass is based on Carbon-12 (12C)
• Very abundant, bonds with most everything
• 1 amu = 1/12 the mass of 12C
• Too small to count
Scientists decided that if 12C = 12 amu, then 12 grams of
carbon = 1 mole of carbon.
• Which is equal to 6.02x1023 atoms of carbon
• 1 mole of anything = its atomic mass in grams
1 atom of oxygen = 16.00 amu
•
1 molecule of H2O = 18.02 amu
•
1 formula unit of NaCl = 58.44amu •
1 mole of oxygen = 16.00 grams
1 mole of H2O = 18.02 grams
1 mole of NaCl = 58.44 grams
Moles & Particles
• Molar Mass = the mass in grams of 1 mole of any
substance.
• AKA gram-formula mass
• Unique for every substance
• Unit: grams per mole (g/mol)
Calculations with Molar Mass
• What is the mass in grams of 2 mole of iron?
• molar mass of Fe = 55.85 g/mol
2 mol Fe x 55.847grams Fe = 111.60 grams Fe
1 mol Fe
Mole/Mass Calculations
Examples:
1. What is the mass of 0.250 moles of magnesium?
Using Periodic Table: 1 mol Mg = 24.31g Mg
0.250 mol Mg x
24.305 g Mg
= 6.08 g Mg
1 mol Mg
2. What is the mass of 5.80 moles of carbon
monoxide? Molar mass of CO = 28.01g/mol
5.80 mol CO x
28.01 g CO
1 mol CO
= 162 g CO
Mole/Mass Calculations
Examples:
1. How many moles would 50.45 grams of neon be
equal to? 1 mol Ne = 20.18g Ne
50.45g Ne x
1 mol Ne
= 2.500 mol Ne
20.18g Ne
2. How many moles would 134.0 grams of
methane(CH4) be equal to? Molar mass of methane =
16.05 g/mol
134.0g CH4 x
1 mol CH4
16.05g CH4
= 8.349 mol CH4