• Molar Mass = mass in grams of one mole– Units grams/mole

• For elements, molar mass = atomic mass

• Why aren’t all atomic masses whole numbers?– Remember that atomic masses are averages of all the

isotopes

H1

C12

O16

Mg24

Molar Mass of Compounds• Add up the molar masses of each individual element

in the compound

• Must multiply the atomic masses by the number of atoms for that element

• Example: BaCl2– Ba = 9.0 g/mol– Cl = 35 g/mol– So, MM = 1(9.0) + 2(35) = 79 g/mol

Calculate the molar mass

• HCl (think H1Cl1)

1* 1.0 + 1* 35 = 36 g/mol

• Al2O3

2 * 27.0 + 3 * 16.0 = 102 g/mol

• C25H52

25 * 12.0 + 52 * 1.0 = 352 g/mol

• C6H12O6

6 * 12.0 + 12 * 1.0 + 6 * 16.0 = 180 g/mol

• Mg(ClO3)2

1* 24 + 2 * 35 + 6 * 16 = 190 g/mol

Calculate the molar mass

• K3PO4

212.3 g/mol

• Ca3(PO4)2

310.3 g/mol

• H2SO4

98.1 g/mol

• (NH4)3PO4

149 g/mol

• BaSO4

233.4 g/mol

• (NH4)3Fe(CN)6

265.8 g/mol

Find the Molar Mass

• BeF2

47 g/mol

• K3P

148.3 g/mol

• (NH4)2O

52 g/mol

• Al(OH)3

78 g/mol

• Ca(NO3)2

164.1 g/mol

• LiNO3

68.9 g/mol

Now we can use molar mass to convert between moles and grams

MolesMass

(grams)

÷ molar mass

x molar mass

Moles to Grams Conversion Reminders

• MUST first calculate molar mass for any conversion involving mass

• Use factor label method to perform conversion

Factor Label Steps

Example Conversions

1) 2 moles C = ? Grams

2) 27 grams H20 = ? Moles

3) 0.75 moles Al(OH)3 = ? Grams

4) 475 grams Br2 = ? moles

Now you try…5) How many grams are in 2 moles of carbon?

6) How many moles are in 27 grams of water?

7) How many grams are in 0.75 moles of aluminum

hydroxide?

8) How many moles are in 475 grams of bromine?

Now we can put two steps together to change from grams particles

Particles (atoms or

molecules)Moles

Mass (grams)

÷ molar mass

x molar mass

x Avogadro’s #

÷ Avogadro’s #

Particles to Grams Conversions Reminders

• MUST first calculate molar mass for any conversion involving mass

• Use factor label method to perform conversion

Factor Label Steps

Example Conversions1) 8.3 grams Ca = ? Atoms

2) 23 grams NaCl = ? formula units

3) 3.01 x 1023 molecules Cl2 = ? Grams

4) 1.204 x 1024 formula units Al2O3 = ? Grams

5) 88 grams CO2 = ? Molecules

6) 4.32 x 1023 formula units BaO = ? grams

Try these…

7) How many atoms are in 8.3 grams of calcium?

8) How many molecules are in 23 grams of sodium chloride?

9) How many formula units are in 88 grams of carbon dioxide?

10) What is the mass in grams of 3.01 x 1023 atoms of chlorine?

11) What is the mass in grams of 1.204 x 1024 molecules of aluminum oxide?

12) What is the mass in grams of 4.32 x 1023 formula units of calcium oxide?

Complete in your notes showing your work!

• Determine the molar mass– K3PO4 – Ca3(PO4)2 – HCl– H2O– BaSO4

• Calculate the moles– 234 g NaCl– 572 g MgCl2– 23 g C6H12O6

• Calculate the mass– 3.45 mol K– 1.75 mol CO2

– 5.2 mol KNO3

– 4.48 mol Ca3(PO4)2

Don’t miss out on these easy

points!

Remember, there are no test

or quiz retakes!!!!