1. The Mole

2. I. Why the Mole? A. Atomic Mass The mass of one atom of an element Measured in amu –1amu = mass of 1 proton = mass of 1 neutron amu is measured in comparison to carbon-12 average mass is listed on the periodic table

3. B. Formula Mass Total mass of the atoms in a given formula H 2 O = H + H + O = NaCl = Na + Cl = H 3 PO 4 = H + H + H + P + O + O + O + O I. Why the Mole? 1 + 1 + 16 amu = 18 amu 23 + 35 amu = 58 amu = 1 + 1 + 1 + 31 + 16 + 16 + 16 + 16 amu = 98 amu

4. C. How do we use this? We can’t measure amu on any scale: they’re too lightweight! For the lab, a mathematical tool I. Why the Mole?

5. “Wouldn’t it be nice if we could keep using the formula mass number. Then I wouldn’t have to remember another number!” “But amu are too small to measure – that’s what the teacher just said!” “We could just use grams, and use the same number.” “What do you mean?” “Well, let’s say that you have some carbon-12. It has a formula mass of 12 amu.” “So?” “We want to keep using that same number, 12, right? So let’s use proportionality.” “Huh?” “Where 1 carbon atom has a mass of 12 amu, there must be some number of atoms that has a mass of 12 grams.” “So 1 carbon atom is to 12 amu as some number of atoms is to 12 grams.” “Right. And we’ll call that number of atoms ‘The Mole.’” “Why?” “Or we could call it ‘Avogadro’s Number’ after the fellow that figured out what that number was.” “What is that number?” “One mole is 6.02 x 10 23 ” “So 1 mole of carbon is 12 grams, and 1 atom of carbon is 12 amu.” “Right.”

6. D. Calculating Molar Mass When the mass in grams of a substance = the formula mass of that substance, you have 6.02 x 10 23 units of that substance I. Why the Mole?

7. D. Calculating Molar Mass The molar mass is the mass of one mole of whatever it is. Calculate the molar mass of the following atoms, compounds and molecules:

8. D. Calculating Molar Mass NaOH Na – 23 amu for every atom, so 23 grams in every mole. O – 16 amu for every atom, so 16 grams in every mole. H – 1 amu for every atom, so 1 gram in every mole. NaOH = 23 g/mol + 16 g/mol+ 1 g/mol = 40 g/mol

9. D. Calculating Molar Mass PbCl 2 Pb – 207 amu for every atom, so 207 grams in every mole. Cl – 35 amu for every atom, so 35 grams in every mole. There’s 2 Cl in every formula, so we need two of them in the mass. PbCl 2 = 207 g/mol + 35 g/mol+ 35 g/mol = 277 g/mol