Chemistry Unit 6: Chemical Quantities Lecture 6.4 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 Mole Volume of gas (STP) Representative Particles Mass Objective: What do you do if you are asked to convert between two units, and neither one is the mole? When calculating chemical quantities, everything goes through the ________________________ If neither of your units is a mole, you will need a ____________-step conversion problem. One ________________ ______________ to go from the given units to __________________, and a second conversion factor to go from moles to the ______________________ units. You know we are talking about MASS if the units are _________________. You know we are talking about VOLUME if the units are ________________. You know we are talking about particles if the units are ________________, _________________, or _________________ ______________. Molar mass 1 mol Representative Particles 1 mol 6.02x1023 particles Mass 6.02x1023 particles 1 mol (atoms, molecules, or formula units) (grams) 1 mol Molar mass

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 g 46.01 g = 1 mol 2nd Equality: Definition of Mole Equality 1 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). 3.24 x 1022 molecules Cl2 x 1 mol x 22.4 L Cl2 = 1 6.022 x 1023 molecules 1 mol 1.21 L Cl2

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.