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“The Mole” and Avogadro’s Number 6.022 x 23 10 Avogadro's Mole Clip http://www.youtube.com/watch?v=gGRQaEsQb1I Avogadros’ Number Molecules and atoms are extremely small objects - both in size and mass. Consequently, working with them in the laboratory requires a large collection of them. How large does this collection need to be? Avogadros’ Number A standard needs to be introduced. This standard is the "mole". The mole is based upon the carbon-12 isotope. Carbon 12 is the most frequently occurring isotope of the element Carbon (98%). Avogadro's Number! We ask the following question: How many carbon-12 atoms are needed to have a mass of exactly 12 g? That number is NA - Avogadro's number. Careful measurements yield a value for NA = 6.0221367x10^+23. 1 mole = 6.022 x 1023 particles of any substance Say What??? EX: if we stack 1 mole of pennies on top of one another, how tall would the stack be? The answer is it would be so tall that the stack of pennies could reach the sun and back almost 500 million times! The mole concept is no more complicated than the more familiar concept of a dozen : 1 dozen = 12 objects. 1 dozen elephants = 12 elephants 1 dozen feathers = 12 feathers Remember???? Dimensional Analysis! 1 mole = 6.022x 1023 atoms of any element! More Examples….. 1 mole of gumballs is 6.022 x 1023 gumballs 1 mole of popcorn is 6.022 x 1023 kernels of popcorn Who weighs more??? Obviously the gumballs, but the quantity is the SAME for both! This much popcorn would cover the entire US 310 miles high! Whew, that’s a lot of poppin’! Moles and Grams The mass in grams of 1 mole of a substance is its “atomic mass”. What is 1 mole of oxygen??? 15.9994 grams (its atomic mass) What is 1 mole of calcium??? 40.08 grams (its atomic mass) Moles and Grams 1 mole of Carbon weighs 12 grams. In other words…6.022 x 1023 atoms of Carbon weighs 12 grams. 1 mole of Chlorine weighs 35.45 grams. In other words… 6.022 x 1023 atoms of Chlorine weighs 35.45 grams. NOTES! Copy these conversions. 1 mole = 6.022 x 1023 atoms 1 mole = molecular weight (in grams) Atomic Mass Unit (amu) This is a unit that describes the mass of a single atom! One single atom of Carbon has a mass of 12 atomic mass units. This is very small. One mole of Carbon (6.022 x 1023 atoms of Carbon) weighs 12 grams. This is very large. Lets remember D.A. What is the mass of exactly 150 gumballs? 10 gumballs = 21.4 g If you want 50 eggs, how many dozens must you buy? If a football player is tackled 1.7 ft short of the end zone, how many more yards does the team need to get a touchdown? 150 gumballs x 21.4 g 1 10 gumballs 50 eggs x 1 dozen 1 12 eggs 1.7 ft 1 x 1 yard 3 ft = = 321 grams 4.2 dozen = 0.57 yards Lets try one together! Determine the mass in grams of 5.50 moles if iron. Put the original number over 1. Decide where the unit needs to go in the next step to cancel out. Decide which conversion you will use, and plug in the numbers. The Answer 5.50 mol Fe x 55.85 g Fe 1 1 mol Fe = 307 g Fe Determine the amount of iron present in 352 grams of Fe. The Answer 352 grams Fe x 1 mole Fe = 6.30 mols Fe 1 55.85 grams Practice Problems How many grams are in 2.50 mols of S? 2. How many grams are in 3.20 mols of Cu? 3. How many mols are present in 11 grams of Si? 4. How many mols are present in 205 g of Hg? 5. What is the mass in grams of 0.48 mol of Pt? 1. Solutions! 1. 2. 3. 4. 5. 80.2 g S 203 g Cu 0.39 mol Si 3.1 mol Hg 94 g Pt