1. Notes #1: Formula Weight & % Composition
WCHS Chemistry
QUIZ FRIDAY!!!
NEED PERIODIC TABLES AND CALCULATOR!!!!

2. CLOSER LOOK: COMPOUNDS
NaHCO3 Na2SO Sr(NO3) Al2(SO4)3
Na =
H =
C =
O = 1
Na =
S =
O = 2
Sr =
N =
O = 1
Al =
S =
O = 2 1 1 2 3 1 4 6 12 3

3. = the total mass of the elements in a compound
FORMULA WEIGHT (FW)
= the total mass of the elements in a compound
Calculating Formula Weight
Find the mass of each individual element
Use whole numbers
Add all of the element masses together
Ex. H2O →
H = 1
O = 16
→ = 18!

4. MORE PRACTICE
NaHCO Sr(NO3)2
Na =
H =
C =
O = 1
Sr =
N =
O = 1 1 2 1 6 3

5. = the mass percent of each element in a compound
PERCENT COMPOSITON
= the mass percent of each element in a compound
To calculate % composition:
element mass x 100
Ex. H2O →
formula weight
H → 2/18 x 100% = 11.1% H
O → 16/18 x 100% = 88.9% O

6. 84 MORE PRACTICE NaHCO3 → 23/84 x 100% Na = H = C = O = 1 x 23
PERCENT COMPOSITIONS!
NaHCO3
→ 23/84 x 100%
Na =
H =
C =
O = 1
x 23
= 27.4% Na
= 23
→ 1/84 x 100%
= 1.2% H 1
x 1
= 1
= 14.3% C
→ 12/84 x 100% 1
x12
= 12
→ 48/84 x 100%
= 57.1% O 3
x16
= 48 + 84
FORMULA WEIGHT!