1. Chapter 7 – Chemical Formulas and Chemical Compounds
7-3: Using Chemical Formulas

2. Formula Mass
The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula.
Ex. Glucose is C6H12O6
C is amu 6 X amu
H is 1.01 amu 12 X amu
O is amu 6 X amu
Formula Mass = amu

3. Formula Mass
H2SO4
Ca(NO3)2
PO43-

4. Molar Mass
The molar mass of a compound is numerically equal to its formula mass, but is expressed in units of g/mol
Molar mass of glucose is g/mol

5. Molar Mass as a Conversion Factor
Convert moles of compound to grams
Convert grams of a compound to moles

6. Molar Mass Practice Problems
How many moles of compound are there in 6.60 g (NH4)2SO4?
What is the mass in grams of 6.25 mol of copper (II) nitrate?
How many molecules are there in 25.0 g of H2SO4?

7. Percentage Composition
Percent, by mass, of each element in a compound.
Divide the mass of element by molar mass of compound and multiply by 100.

8. Percentage Composition
Find the percentage composition of copper (I) sulfide, Cu2S

9. Hydrates
Hydrates are crystalline compounds in which water molecules are bound in the crystal structure.
Na2CO3·10H2O
There are 10 water molecules for every formula unit of sodium carbonate in the crystal.
The dot means that the water is loosely attached in the crystal. It does NOT mean to multiply when determining the molar mass.

10. Hydrates/Percentage Composition
Find the mass percentage of water in ZnSO4·7H2O

11. Percentage Composition
Magnesium hydroxide is 54.87% oxygen by mass. How many grams of oxygen are in 175 g of the compound? How many moles of oxygen is this?