Warm-Up

Calculate Molar Mass1.K2O

2.PCl5

3.LiF

The Mole...J. McLeod

Objectives

• Describe methods of measuring the amount of something.• Define Avogadro’s number as it relates to a mole of a

substance.• Distinguish between the atomic mass of an element and its

molar mass.• Describe how the mass of a mole of a compound is

calculated.• Describe how to convert the mass of a substance to the

number of moles of a substance, and moles to mass.• Describe how to convert the volume of a substance to the

number of moles of a substance, and moles to volume.

The mole… Abbreviated (mol)

• It is an amount, such as…o Pair: 1 pair of shoelaces = 2 shoelaceso Dozen: 1 dozen oranges = 12 orangeso Gross: 1 gross of pencils = 144 pencilso Ream: 1 ream of paper = 500 sheets of paper

Definition

1 mole = 6.02 x 1023

That’s 602,000,000,000,000,000,000,000

We call this number Avogadro’s number after Amadeo Avogadro

(1766-1856)

Definition

Field Trip!!!!

Definition

= 1 mol C

= 12 grams C

= 6.02 x 1023 atoms C

Review

• Atomic Mass is the average of all isotopes of a given element.

• 1 amu = 1/12 of a C-12 atom.

Molar Mass

• Atomic Mass = Molar Mass for an element

• Molar mass is the mass of 1 mole of a compound.

• It is calculated by adding each of the atomic masses of the elements making up the compound.

• Units for molar mass are g/mol.

Diatomics

• Diatomics…. You need a highlighter!!

Calculating Molar Mass

Example #1: What is the molar mass of carbon (C)?

C: 1 x 12.00 = 12.00 g/mol1 mole of carbon = 12 grams of carbonExample #2: What is the molar mass of oxygen (O2)?

O: 2 x 15.99 = 31.98 g/mol1 mole of oxygen = 31.98 grams of oxygen.

Calculating Molar Mass

Example #3: What is the molar mass of Water (H2O)?

H: 2 x 1.008 = 2.016 g/molO: 1 x 15.99 = 15.99 g/mol

H2O = 18.006 g/mol1 mole of water = 18.006 grams of water

Calculating Molar Mass

Example #4: What is the molar mass of sodium chloride (NaCl)?Na: 1 x 22.99 = 22.99 g/molCl: 1 x 35.45 = 35.45 g/mol

NaCl = 58.44 g/mol1 mole of NaCl = 58.44 grams of NaCl

Your Turn

Calculate the molar mass for lithium dichromate: Li2Cr2O7

1 mole of Li2Cr2O7 = ___________ g of Li2Cr2O7

Conversion Road Map

Using the flowchart we can convert between moles, mass, molecules, or liters:

6.02x1023

Molar mass

22.4

Molecules, atoms, or ions

Moles

Grams

Liters

Rules For Conversion

1. Write Units Map2. Set Up Problem

a. Write Givenb. Use a T box for each step of the mapc. Make sure your units cancel!

3. Write your answer with correct units

Use Of Molar Mass

How many grams of nitrogen are in 1.25 moles of nitrogen (_______)?Units Map: mol (N2) grams (N2)

1.25 mol N2

mol N2

grams N2

128 = 35.0 g N2

What’s the formula for Nitrogen?

Use of Avogadro’s Number

How many atoms of iron are in 2.76 moles of the metal?Map: mol Fe atoms Fe

2.76 moles Fe

moles Fe1

6.022 x 1023= 1.61 x 1024 atoms Fe

atoms Fe

Use of Volume

How many moles of carbon monoxide are in 26.7L of carbon monoxide?Units Map L CO mol CO

26.7 L CO

L CO22.4

1 = 1.19 mol CO

mol CO

Use of Molar Mass & Avogadro’s #

How many molecules of Iodine are in 25g of Iodine (____)?Units g I2 mol I2 molecules I2

25 g I2

g I2253.81

1

=5.93x1022 molecules I2

mol I2

1 mol I2

6.022x1023 molecules I2

I2

Ticket Out The Door

• In your groups, compare and contrast the process to convert moles to grams and that to convert moles to atoms or particles.

• WHAT’S SIMILAR?• WHAT’S DIFFERENT?