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

• Molar Mass = atomic mass

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

isotopes

H1.0

C12.0

O16.0

Mg24.3

• Molecular mass = protons + neutrons = amu (amu = atomic mass units)

• Hydrogen atom has 1 proton = 1 amu

• Oxygen atom has 8 protons and 8 neutrons = 16 amu

Calculate the molar mass• HCl (think H1Cl1)

1* 1.0 + 1* 35.5 = 36.0 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* 24.3 + 2 * 35.5 + 6 * 16.0 = 191.3 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

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

Particles(atoms or

molecules)

MolesAvogadro’s Number

6.02 x 1023 particles/mole

÷

x

• How many grams are in 2 moles of carbon?– Molar mass of carbon = atomic mass = 12 g/mol

• How many moles are in 27 grams of water?– Molar mass of water = 2 x 1.0 + 1 x 16.0 = 18.0 g/mol

– Essentially what you have 27 ÷ 18 = 1.5 moles

gramsmolegramsxmoles 241122

waterofmolesgramsmolexgrams 5.1

18127