Calculations with Molar Mass of Compounds
MOLE ROAD
MASS
MOLES
Molar Mass
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 (𝑔)
1 𝑚𝑜𝑙
𝑜𝑟
1 𝑚𝑜𝑙
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 (𝑔)
-
Avogadro’s #
PARTICLES
6.02 × 10!" 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
1 𝑚𝑜𝑙𝑒
𝑜𝑟
1 𝑚𝑜𝑙
6.02 × 10!" 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠
conversion factor between mass and mole calculations just like w/elements
o calculate the molar mass of the compound first
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 (𝑔)
1 𝑚𝑜𝑙𝑒
𝑜𝑟
1 𝑚𝑜𝑙𝑒
𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑 (𝑔)
Example #1: Moles
Mass
How many moles PCl3 are in 85.9g PCl3?
Calculate MM of PCl3 **Show your work!!**
P = 1 mol x 30.97 g/mol = 30.97 g/mol
Cl = 3 mol x 35.45 g/mol = 106.35 g/mol
+ ---------------------------------------137.32 g/mol
? mol PCl3 = 85.9 g PCl3
1 mol PCl3
----------------------------------------------- = 0.626 mol PCl3
137.32 g PCl3
mole
Example #2: Mass
Particles
How many g PCl3 in 5.23 x 1024 mlcl PCl3??
MM PCl3 = 137.32 g/mol *from previous problem
? 𝑔 𝑃𝐶𝑙! =
5.23×10!" 𝑚𝑙𝑐𝑙 𝑃𝐶𝑙!
×
1 𝑚𝑜𝑙 𝑃𝐶𝑙!
137.32 𝑔 𝑃𝐶𝑙!
×
= 1.19 × 10! 𝑔 𝑃𝐶𝑙! 𝑜𝑟 1190 𝑔 𝑃𝐶𝑙!
6.022×10!" 𝑚𝑙𝑐𝑙 𝑃𝐶𝑙!
1 𝑚𝑜𝑙 𝑃𝐶𝑙!
Moles and Mass of the Compound and Element
Mass Compound
Moles Compound subscripts
Moles Element
Example:
How many grams of H are there in 75.4 g CH4 (methane)?
g CH4 àmol CH4 àmol H à g H
- 4 mol H/1 mol CH4
- MM CH4 = 16.05 g/mol
Mass Element
MM CH4
1 mol C x 12.01 g/mol
4 mol H x 1.008 g/mol
+_______________________
16. 04 g/mol
? g H= 75.4 g CH4
1 mol CH4
4 mol H
1.008 g H
------------------------------------------------------------------------------------------------- = 19.0 g H
16.04 g CH4
1 mol CH4
1 mol H
4.70 mol CH4
18.8 mol H