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The Mole

The Mole. 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. I. Why the Mole?. B. Formula Mass

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The Mole

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  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. I.Why the Mole? B.Formula Mass • Total mass of the atoms in a given formula H2O = H + H + O = NaCl = Na + Cl = H3PO4 = H + H + H + P + O + O + O + O 1 + 1 + 16 amu = 18 amu 23 + 35 amu = 58 amu = 1 + 1 + 1 + 31 + 16 + 16 + 16 + 16 amu = 98 amu

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

  5. “Wouldn’t it be nice if we could keep using the formula mass number. Then I wouldn’t have to remember another number!” “We could just use grams, and use the same number.” “Well, let’s say that you have some carbon-12. It has a formula mass of 12 amu.” “Where 1 carbon atom has a mass of 12 amu, there must be some number of atoms that has a mass of 12 grams.” “Right.” “Right. And we’ll call that number of atoms ‘The Mole.’” “Or we could call it ‘Avogadro’s Number’ after the fellow that figured out what that number was.” “One mole is 6.02 x 1023” “We want to keep using that same number, 12, right? So let’s use proportionality.” “Huh?” “So 1 carbon atom is to 12 amu as some number of atoms is to 12 grams.” “What do you mean?” “Why?” “But amu are too small to measure – that’s what the teacher just said!” “So?” “So 1 mole of carbon is 12 grams, and 1 atom of carbon is 12 amu.” “What is that number?”

  6. I.Why the Mole? D. Calculating Molar Mass • When the mass in grams of a substance = the formula mass of that substance, you have 6.02 x 1023 units of that substance

  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 PbCl2 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. PbCl2 = 207 g/mol + 35 g/mol+ 35 g/mol = 277 g/mol

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