The Mole Road Map

Chemistry

Unit 6: Chemical Quantities

Lecture 6.4

Objectives

• Convert a quantity of a chemical between moles, mass (g), particles, and volume.

ALL About the Mole…

• We have now looked at the mole in terms of mass (g), particles, and volume.

• HOWEVER…in order to do these conversions, one of our units had to be the mole.

• What do you do, if you are asked to convert between two units and neither one is mole?

Everything Goes Through The Mole!

• To convert from one unit to another, you must use the mole as an intermediate step.

• In other words…you might need a “two-step” conversion problem.

What is a “Two-Step” Conversion Problem?

• Two conversion factors– One to convert from given unit to moles– One to convert from moles to wanted unit

Mole Road Map

Mass

Representative Particles

Mole

22.4 L

1 mol

1 m

ol

22.4

L

1 mol

6.02x10 23 particles

Molar mass

1 mol

1 m

ol

Mola

r mas

s

6.02x1023 particles

1 mol

(grams) (atoms, molecules, or formula units)

Volume

of gas

(STP)

Here’s An Example

Calculate the number of molecules in 60.0 g NO2.

Given: 60.0 g NO2

1st Equality: Molar Mass Equality

molar mass NO2 : 46.01 g46.01 g = 1 mol

2nd Equality: Definition of Mole Equality1 mol = 6.02 x 1023 molecules

So here’s the equation:

60.0 g NO2 x 1 mol x 6.02 x 1023 molecules =

1 46.01 g NO2 1 mol

7.85 x 1023 molecules NO2

Another Example

Calculate the volume, in liters, of 3.24 x 1022 molecules of Cl2 (STP).

1.21 L Cl2

3.24 x 1022 molecules Cl2 x 1 mol x 22.4 L Cl2 = 1 6.022 x 1023 molecules 1 mol

What Now?

• You will NOT be allowed to use your “Road Map” on the test, so you need to practice enough that you no longer rely on it to help you through solving these problems.