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The mole concept involves the concept of the weights of substances.

The mole concept involves the concept of the weights of substances. We must first understand the meaning of the terms "atomic weight," and "molecular weight,". Atomic weights represent the relative weights of different atoms. Atomic, and molecular weights are expressed in atomic mass units.

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The mole concept involves the concept of the weights of substances.

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  1. The mole concept involves the concept of the weights of substances.

  2. We must first understand the meaning of the terms "atomic weight," and "molecular weight,"

  3. Atomic weights represent the relative weights of different atoms.

  4. Atomic, and molecular weights are expressed in atomic mass units.

  5. Chemists invented the concept of the mole because they needed a way to ''count" atoms and molecules.

  6. Since atoms and molecules are far too small and far too numerous to actually count,

  7. we must be able to achieve this "counting" by some indirect method.

  8. Take Ba + I2 >> Ba I2 We can see that if we add one atom of Ba and one molecule of I2 it will form the desired product

  9. Well we could just count out the atoms that we need to the exact amount then do the reaction so there is no waste

  10. It would take the entire population of the world a gazillion years to count the atoms in the smallest piece of matter.

  11. The problem is we can’t see them and the numbers are unbelievably large.

  12. Ba = 137.3 amu and I2 = 2(126.9) = 253.8amu

  13. well we can see that I2 is heavier than Ba. How much heavier?

  14. 253.8/137.3 = 1.85 it is 1.85 times heavier.

  15. If you had a football player and a cheer leader. Say the football player weighed 253.8lb and the cheerleader weighed 137.3lb

  16. the football player would be 1.85 times heavier than the cheerleader

  17. What if the cheerleader and football player had Identical twins

  18. 2football player/ 2cheerleader = ?

  19. 1.85 What about 10football player/ 10cheerleader?

  20. 100000football player/ 100000cheerleader? Equal 1.85

  21. So (X) football player/ (X) cheerleader = 1.85

  22. 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.

  23. 1( gazillion) / 2 ( gazillion) = 1/ 2 =.5

  24. Your in the lab and you want to run an experiment and don’t want to waste anything

  25. With great skill you do the following

  26. you reach in and pull out exactly 253.8 grams of I2 and 137.3 grams of Ba

  27. So if I’m holding a sample of I2 that is 1.85 times heavier than my sample of Ba. I can say something very important

  28. THE POINT! At this point we know that the number of I2 molecules and the number of Ba molecules are the same.

  29. Just as 10 football players weighed 1.85 times more than 10 cheerleaders

  30. 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.

  31. 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.

  32. A mole of any substance contains the same number of "particles" as a mole of any other substance.

  33. Ba =137.3 amu A mole of Ba = 137.3 grams

  34. I2 = 253.8 amu A mole of I2 =253.8 grams

  35. 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

  36. A dozen eggs = 12 eggs, but how many people in a dozen people?

  37. What a dozen or a mole of something weighs, depends upon what it is.

  38. Well if there are 12 in a dozen than how many are there in a mole? A LOT!!

  39. The number of particles in a mole is equal to 6.02 E23, an unimaginably large number.

  40. 6.02E23 = 6.02 X1023

  41. 602,000,000,000,000,000,000,000 of something

  42. When the molecular weight of a substance is expressed in grams, it is referred to as the molar mass of the substance.

  43. Find the molar mass of H2O • 2H = 2(1) = 2 grams • 1O = 1(16) =16 grams • H2O = 18 grams

  44. Calculate the molar mass of HNO3 • H = 1(1) = 1 grams • N = 1(14) = 14 grams • O = 3(16) = 48grams • HNO3 = 63 grams

  45. Calculate the molar mass of HC2H3O2 • H = 1(4) = 4 grams • C = 2(12) = 24 grams • O = 2(16) = 32 grams • HC2H3O2 = 60 grams

  46. Practice • 1) Na2S • 2) Al(OH)3 • 3) (NH4)2SO4 • 4) C6H12O6

  47. Answer

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