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

Mass (grams)

Mole Road Map

Volume of gas (STP) Mole Representative Particles (atoms, molecules, or formula units)

Here’s An Example

Calculate the number of molecules in 60.0 g NO 2 .

Given: 60.0 g NO 2 1 st Equality: Molar Mass Equality molar mass NO 2 : 46.01 g 46.01 g = 1 mol 2 nd Equality: Definition of Mole Equality 1 mol = 6.02 x 10 23 molecules

So here’s the equation: 60.0 g NO 2 x 1 mol 1 46.01 g NO 2 x 6.02 x 10 23 molecules 1 mol = 7.85 x 10 23 molecules NO 2

Another Example

Calculate the volume, in liters, of 3.24 x 10 22 molecules of Cl 2 (STP).

3.24 x 10 22 molecules Cl 2 1 x 1 mol 6.022 x 10 23 molecules x 22.4 L Cl 2 1 mol = 1.21 L Cl 2

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.