Molar Mass, section 7.2

A. The Molar Mass of a Substance 1) Define Molar Mass = the mass (in grams) of one mole of any element or compound Generic for saying… –“atomic mass” –“formula mass” –“molecular mass”

Molar Mass 2) There are situations where “molar mass” doesn’t work well –For example, what is the molar mass of oxygen? DON’T KNOW (O or O 2 ?) –What is better? Asking for the gram atomic mass or the gram molecular mass –List the 7 diatomic molecules for review

Using Molar Mass to convert between moles and mass Sample Calculations on page 4

B. The Volume of a mole of gas 1. Unlike liquids and solids, the volumes of moles of gases are much more predictable under the same physical conditions of temperature and pressure. 2. We report standard conditions to report volumes of gases.

Standard Temperature and Pressure 3. STP is equal to … –0 o C (273 Kelvin) [standard temp] –101.3 kilopascals (kPa) [standard pressure] 4. ONE MOLE OF ANY GAS AT STANDARD CONDITIONS OCCUPIES A VOLUME OF 22.4 LITERS 5. This quantity is called the MOLAR VOLUME.