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 H 1.0 C 12.0 O 16.0 Mg 24.3
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 H 1 Cl 1 ) 1* * 35.5 = 36.0 g/mol Al 2 O 3 2 * * 16.0 = 102 g/mol C 25 H * * 1.0 = 352 g/mol C 6 H 12 O 6 6 * * * 16.0 = 180 g/mol Mg(ClO 3 ) 2 1* * * 16.0 = g/mol
Calculate the molar mass K 3 PO g/mol Ca 3 (PO 4 ) g/mol H 2 SO g/mol (NH 4 ) 3 PO g/mol BaSO g/mol
Now we can use molar mass to convert between moles and grams Particles (atoms or molecules) Moles Avogadro’s Number 6.02 x 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 x 16.0 = 18.0 g/mol –Essentially what you have 27 ÷ 18 = 1.5 moles