Chapter 4 Notes

Chapter 4 Notes - September 10, 2007 Counting Tiny Things...

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September 10, 2007 Counting Tiny Things If you need to count a great many identical things, it’s usually easiest to count a subset of them and measure some bulk property of that subset of them, then measure the bulk property for the whole quantity. We can use the factor-label method to do this. 200 1$ bills make a stack approx. 1 in high. Id we have a stack 6 inches high we can calculate the approx. value. (200 bills/inch stack) x 6 inch stack = 1200 bills Another example: I’ve got jar with about 3.5 lbs of quarters in it. I weighed 20 quarters, and they weighed 2.5 oz. How much money is in my jar? We start with 3.5 lbs of quarters. We multiply y the conversion factor from pounds to ounces. We cancel the pounds. We multiply by a conversion factor from ounces to number of quarters. The ounces cancel. We multiply by the quarter to dollar conversion factor. The quarters cancel, giving us an answer. Counting Atoms Same thing. only now doing something chemical. How many atoms are there in a3.54 g of Nickel. Nickel has an atomic mass of 58.6934 amu and 1 amu = 1.6605 x 10^-24 g. We start with 2.54 grams of Nickel. We multiply by the conversion factor from grams to amu. We cancel the grams. We divide tbyt eh atomic mass of Nickel. 3.54 g x (1 amu/1.66 x 10^-24) x (1 atom/58.7 amu) = 2.62 x 10^22
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Chapter 4 Notes - September 10, 2007 Counting Tiny Things...

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