The Mole Concept

Chemistry

What is a mole?

• The mole is a unit used to measure very small quantities– Such as atoms, particles, molecules,

ions, etc.– One mole = 6.022 x 1023

• The mole is similar to the concept of a dozen– One dozen = 12

? ?

=One Dozen

=One Mole 6.022 x 1023

12.00 g of Carbon!

One mole can represent many things!

One dozen would be…• 12 eggs• 12 atoms• 12 chemistry teachers

One mole would be…• 6.02 x 1023 eggs• 6.02 x 1023 atoms• 6.02 x 1023 chemistry

teachers!

Boy that’s a lot of bored students!

Amadeo Avogadro

• The concept of the mole is attributed to Avogadro, and is referred to as Avogadro’s number

A Mole Can Represent Anything

• Atoms• Molecules• Particles• Planets• Coins

Mole Conversions

• Example Problems1. If I have 3 moles of He gas, how many

particles is this?

2. If I have 8.0 x 1024 atoms of iron, Fe, how many moles is this?

1.81 x 1024 particles He

13.3 mol Fe

DOES EVERY MOLE HAVE THE SAME

MASS?

One Mole (6.02 x 1023) is…

Potassium dichromate

294 grams

Zinc metal

65.4 grams

Molar Mass

• The mass of one mole of a substance– Based on their atomic masses on the

periodic table– By convention, we will round atomic

masses to 3 sig figs–Molar masses can be used as a

conversion factor

• Molar Mass has units of grams per mole (or g/mol)

Molar Mass

• Example Problems1. What is the molar mass of iron?

2. How many grams of iron are there in 8.00 moles?

55.8 g/mol Fe

446 g Fe

Molar Mass

• Example Problems3. How many moles are in 10.0 grams of

magnesium?

4. How many moles are in 5.3 grams of boron?

0.412 mol Mg

0.491 mol B

Molar Mass

• Practice Problems1. How many grams of sulfur are there in

2.5 moles?

2. How many grams of aluminum are there in 2.00 moles?

80.3 g S

54 g Al

Molar Mass

• Practice Problems3. How many moles are there in 3.4

grams of carbon?

4. How many moles are there in 2.00 grams of neon?

0.283 mol C

0.099 mol Ne

Molar Mass of Molecules

• Using the molar mass for each element, find the total molar mass of a molecule

• Example Problems1. What is the molar mass of H2O?

2. What is the molar mass of CO2?

18.02 g/mol H2O

44 g/mol CO2

Molar Mass of Molecules

• Practice Problems1. What is the molar mass of C3H8?

2. What is the molar mass of CH3I?44.1 g/mol C3H8

142 g/mol CH3I

Molar Mass of Molecules

• Example Problems1. If I have 5.00 grams of NaCl, how many

moles is this?

2. If I have 4.50 moles of water, H2O, how many grams is this?

0.0901 mol NaCl

81.1 g H2O

Molar Mass of Molecules

• How many particles are there in 3.00 grams of ammonia (NH3)?

1.06 x 1023 particles NH3

Molar Mass of Molecules

• Practice Problems1. How many moles are in 1.2 grams of

methane gas (CH4)?

2. How many grams are in 4.3 moles of propane (C3H8)?

0.0665 mol CH4

189 g C3H8

Molar Mass of Molecules

• How much do 1.3 x 1024 atoms of H2O weigh (in grams)? (2 steps!)

0.389 g H2O