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The mole concept involves the concept of the weights of substances.
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We must first understand the meaning of the terms "atomic weight," and "molecular weight,"
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Atomic weights represent the relative weights of different atoms.
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Atomic, and molecular weights are expressed in atomic mass units.
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Chemists invented the concept of the mole because they needed a way to ''count" atoms and molecules.
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Since atoms and molecules are far too small and far too numerous to actually count,
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we must be able to achieve this "counting" by some indirect method.
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Take Ba + I 2 >> Ba I 2 We can see that if we add one atom of Ba and one molecule of I 2 it will form the desired product
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Well we could just count out the atoms that we need to the exact amount then do the reaction so there is no waste
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It would take the entire population of the world a gazillion years to count the atoms in the smallest piece of matter.
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The problem is we can’t see them and the numbers are unbelievably large.
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Ba = 137.3 amu and I 2 = 2(126.9) = 253.8amu
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well we can see that I 2 is heavier than Ba. How much heavier?
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253.8/137.3 = 1.85 it is 1.85 times heavier.
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If you had a football player and a cheer leader. Say the football player weighed 253.8lb and the cheerleader weighed 137.3lb
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the football player would be 1.85 times heavier than the cheerleader
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What if the cheerleader and football player had Identical twins
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2football player/ 2cheerleader = ?
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1.85What about 10football player/ 10cheerleader?
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100000football player/ 100000cheerleader? Equal 1.85
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So (X) football player/ (X) cheerleader = 1.85
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The ratio of weights of a large but equal number of objects is the same as the ratio of weights of one of each of these objects.
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1( gazillion) / 2 ( gazillion) = 1/ 2 =.5
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Your in the lab and you want to run an experiment and don’t want to waste anything
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With great skill you do the following
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you reach in and pull out exactly 253.8 grams of I 2 and 137.3 grams of Ba
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So if I’m holding a sample of I 2 that is 1.85 times heavier than my sample of Ba. I can say something very important
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THE POINT! At this point we know that the number of I 2 molecules and the number of Ba molecules are the same.
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Just as 10 football players weighed 1.85 times more than 10 cheerleaders
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If I didn’t know how many football players and cheerleaders there were but, I knew the ratio was 1.85 then I would at least know they were equal.
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The mole is defined as a quantity of a substance whose mass is equal to its atomic or molecular weight expressed in grams instead of amu's.
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A mole of any substance contains the same number of "particles" as a mole of any other substance.
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Ba =137.3 amu A mole of Ba = 137.3 grams
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I 2 = 253.8 amu A mole of I 2 =253.8 grams
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A mole of anything has the same number of “things” as a mole of anything else. A mole of people or a mole of cars
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A dozen eggs = 12 eggs, but how many people in a dozen people?
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What a dozen or a mole of something weighs, depends upon what it is.
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Well if there are 12 in a dozen than how many are there in a mole? A LOT!!
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The number of particles in a mole is equal to 6.02 E 23, an unimaginably large number.
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6.02E 23 = 6.02 X10 23
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602,000,000,000,000, 000,000,000 of something
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When the molecular weight of a substance is expressed in grams, it is referred to as the molar mass of the substance.
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Find the molar mass of H 2 O 2H = 2(1) = 2 grams 1O = 1(16) =16 grams H 2 O = 18 grams
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Calculate the molar mass of HNO 3 H = 1(1) = 1 grams N = 1(14) = 14 grams O = 3(16) = 48 grams HNO 3 = 63 grams
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Calculate the molar mass of HC 2 H 3 O 2 H = 1(4) = 4 grams C = 2(12) = 24 grams O = 2(16) = 32 grams HC 2 H 3 O 2 = 60 grams
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Practice 1)Na 2 S 2)Al(OH) 3 3)(NH 4 ) 2 SO 4 4)C 6 H 12 O 6
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Answer
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Converting Set up to find the number of eggs in 4 dozen dozen eggs 4 dozen 1 dozen 48 eggs 12 eggs = =
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Converting Set up to find the number of Dozens in 43 eggs eggs dozen 1dozen 43 eggs 12 eggs 3.6 dozen 1 dozen = =
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Mols KCl Grams KCl 1. What is the mass of 2.0 moles of KCl ? 2 Mols KCl 1 Mols KCl 141 G KCl 75.5G KCl = =
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What is the mass of 0.75 moles of CuSO 4 ? Mols CuSO4 Grams CuSO4.75 Mols CuSO4 1 Mols CuSO4 119.7 G CuSO4 159.55G CuSO4 = =
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Calculate the number of mols in 30.2 grams of LiNO 3 One molar mass of LiNO 3 = 68.94g g LiNO 3 Mol LiNO 3 30.2 g LiNO 3 68.94 g LiNO 3.43 Mol LiNO 3 1 Mol LiNO 3 = =
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How many atoms are in a. 2.56 mols selenium Mols Se Atoms Se 2.56Mols Se 1 Mols Se 1.54E 24 Atoms Se 6.02E 23 Atoms Se = =
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