1. Moles Mass
There is also a connection between 1 mole of a substance and mass of any element or compound.
Use Molar Mass to convert between moles
& mass.
Mass Unit = grams

2. Moles
Mass
Conversion Factor:
1 mol = molar mass (grams)

3. EXAMPLES: Moles to Mass
1. How many grams are in 5.42 moles of NaCl?
2. How many moles are in 83.6 grams of H2O?

4. EXAMPLES: Mass to Moles
3. How many grams of tin are in 7.9 moles of tin?
4. How many grams are in 3.34 moles of Na2CO3?

5. Percent Composition
The purpose of percent composition is to allow a scientist to determine the percent of mass an element contributes to a whole compound.

6. Example #1 chlorine in KCl?  What is the percent composition of
 Step 1:
 Find the weight of the compound by using the molar mass
 (1 x ) + (1 x )
 Molar Mass of KCl = g

7. Example #1 Continue in KCl?  Step 2:
 What is the percent composition of chlorine
in KCl?
 Step 2:
 Find the weight of the PART you want by using the molar mass.
 Cl =

8. Example #1 Continue KCl?  Step 3:
 What is the percent composition of chlorine in
KCl?
 Step 3:
 Use the percent composition formula (MEMORIZE) & round answer to 3 significant figures.
 Formula: (Part/Whole) x 100
 Work: %Cl = ( / ) x 100
 Answer with correct sig figs: %Cl = 47.6%

9. Example #2
 What is the percent composition of
oxygen in KMnO4?

10. Example #3
 Find the Percent Composition of Mg in
MgCl2?

11. Example #4 element in Fe(NO3)3?
 What is the percent composition of each
element in Fe(NO3)3?