1. Percent Composition

2. Percent by mass of a particular element in a compound % Element = Mass of Element x 100 Mass of Compound

3. Example Find the percentage composition of copper (I) sulfide.

4. Practice 1)Find the percent of nitrogen in (NH 4 ) 2 CO 3 2)Find the percent composition of Ba(NO 3 ) 2

5. Hydrates Some salt crystals bind water molecules in their crystal structure – called hydrates The formula below shows a hydrate with a ratio of 10 water molecules per one salt molecule Na 2 CO 3 10 H 2 O

6. Example Find the percent of water in Na 2 CO 3 10 H 2 O

7. Practice Find the percent of water in ZnSO 4 7 H 2 O