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Avogadro and the Mole

Avogadro and the Mole. Amadeo Avogadro 1776-1856. Italian lawyer turned scientist Famous for proposing that equal volumes of gases held at same temperature and pressure must have the same number of gas particles (Avogadro’s Hypothesis-1811)

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Avogadro and the Mole

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  1. Avogadro and the Mole

  2. Amadeo Avogadro1776-1856 • Italian lawyer turned scientist • Famous for proposing that equal volumes of gases held at same temperature and pressure must have the same number of gas particles (Avogadro’s Hypothesis-1811) • Several scientist attempted to measure how many gas molecules are in a specific volume of gas • Robert Millikan determined the charge of the electron • When scientists divided the charge of a set amount of electrons by the charge of a single electron they calculated the number 6.022 x 10 23 aka Avogadro’s Number (NA)

  3. Scientist began relating the masses of different elements and set up a relative mass scale. They compared C-12 to H-1

  4. Relative Atomic Masses Were Formed • Chemists compared the common Carbon-12 isotope to the smallest element Hydrogen-1. • Carbon-12 was 12 times as “heavy” as Hydrogen-1, so chemists made it easy on themselves and said that Hydrogen = 1 atomic mass unit (amu) and Carbon = 12 amu • Some other comparisons to Hydrogen • Calcium = 40 amu (40x heavier than H-1) • Sulfur =32 amu (32 x heavier than H-1)

  5. Formula Masses Example of Formula Mass • Once Chemists had relative masses of all the elements they could determine how much molecules “weighed” by adding all the amu values for all the elements in a molecule-this is called formula mass. • H2O Formula Mass • 2 Hydrogen atoms x1 amu for each H atom = 2 amu • 1 Oxygen atom = 16 amu • 2 amu (from H) + 16 amu (from O) = 18 amu • 1 Water molecule has a mass of 18 amu

  6. Practice: Calculate the Formula Mass for CaSO4 • Ca = 40 amu • S = 32 amu • O=4 oxygen atoms x 16 amu each = 64 amu • 40 amu + 32 amu + 64 amu = 136 amu • 1 molecule of Calcium sulfate “weighs” 136 amu

  7. Chemists came up with a quantity for comparing the amounts of substances and called it “The Mole” • 1 Mole of any substance is called Avogadro’s Number 6.022 x 10 23. • Insanely huge Number!! • 1 mole of marshmallows would be enough marshmallows to make a 12 mile thick layer of marshmallows covering the entire face of the Earth!! • A pair = 2 things • A dozen = 12 things • A gross = 144 things • A mole = 6.022 x 10 23 things

  8. Molar Mass (MM) • The amu is far too small for chemists to measure in lab. • Since all element masses were relatively compared to each other, chemist use the mass unit gram to measure solids in the lab. • This is really convenient! Since Hydrogen is 1 amu and Carbon is 12 times as “heavy” at 12 amu, chemists changed the value of amu to gram so that they could measure in lab. • One mole of H = 1 gram (This is the molar mass of H) • One mole of C =12 grams (Carbon molar mass)

  9. Practice: Calculate the Molar Mass for CaSO4 • Ca = 40 grams • S = 32 grams • O=4 oxygen atoms x 16 grams each = 64 grams • 40 grams + 32 grams + 64 grams = 136 grams • Does this look familiar?? • 1 molecule of Calcium sulfate “weighs” 136 amu • 1 mole of Calcium sulfate “weighs” 136 grams

  10. Finally Over! Something to Think About. • If you had one dozen dump trucks, pencils, and babies (yeah babies why not?) you would have 12 of each type of thing, but what would be different about them? • Their Masses would be different. • If you had one mole dump trucks, pencils, and pickles, you would have 6.022x 10 23 of each but they would not “weigh” the same!! • Make Sense?! • Happy Mole Day to You • http://www.youtube.com/watch?v=ReMe348Im2w

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