1. Percentage Composition
An Analytical Chemistry Technique

2. I CAN calculate the PERCENTAGE COMPOSITION of a compound from Formula Weight data.

3. Percentage Composition
An analytical chemistry technique used in studying composition of substance is Percentage Composition.
In Percentage Composition, Formula Weight (Molar Mass) data is used to determine the overall contribution the mass of each element makes to the mass of a compound.

4. Calculating Percentage Composition
Determine the FW (MM) of the compound.
Divide the TOTAL MASS of each element by the FW for the compound.
Multiply the results by 100 to convert to a percentage.
Add all percentages to check the answer…it should be VERY CLOSE to 100% (may be slightly off due to rounding).

5. Practice Problem
What is the percentage composition of Magnesium Hydroxide, Mg(OH)2 ?
STEP 1. Calculate the FW:
1 mole Mg X g = g/mole
2 moles O X g = g/mole
2 moles H X g = g/mole
+ _____________
g/mole
(Since this isn’t the last step, don’t round to SF here)

6. STEP 3. Add all the %s to check answer:
STEP 2. Divide EACH ELEMENT’S TOTAL MASS by the FW:
Mg = g X = % g
O = g X = %
H = g X = %
STEP 3. Add all the %s to check answer:
= % = 100%
STEP 4. Report the final answer:
Mg = % O=54.867% H=3.4565%

7. ASSIGNMENT
For each of the following, calculate the PERCENTAGE COMPOSITION of each element!
1. Aluminum Sulfate
2. Sucrose (C12H22O11)
3. Potassium Permangante Tetrahydrate
4. Ammonium Phosphate Dihydrate