1. 7.3 Using Chemical Formulas  Review  Mole: SI unit for the amount of a substance (contains avogadro’s number of particles)  Avogadro’s Number: 6.022 x 10 23 particles/molecules/formulas units per 1 mol  Formula Unit: smallest ratio of cations to anions

2. 2) Formula Mass  Sum of the average atomic masses of all atoms represented in a formula (Units: amu)  Ex: What is the formula mass of Ca(NO 3 ) 2 ?

3. 3) Molar Mass  mass of one mole of any substance (contains avogadro’s number of particles) Units: g/mol  Ex: calculate the molar mass of Al 2 S 3

4. 4) Problem Solving Using Molar Mass  A) Mol to mass  Ex: What is the mass (grams) of 3.0 mol of NaOH?  1. determine molar mass of NaOH  2. # of moles of NaOH x molar mass

5.  B) mass to mol  How many moles are in 135 g of NaOH?  1. determine molar mass of NaOH  2. grams of NaOH / molar mass

6.  C) Moles to molecules / molecules to moles  How many molecules of H 2 0 are present in 1.5 mol?  1. mol NaOH x Avogadro’s #

7. 6. Determining % Composition  A) from chemical formula  Ex – Find the % composition of copper (II) sulfate?  Formula -> molar mass -> mass of each element as %  (disregard letter 6.B)

8. 6) Determing % Composition  B) from mass data