UNIT ANALYSIS 2 or more factors

UNIT ANALYSIS 2 or more factors - grams of Cu 1 mole Cu...

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UNIT ANALYSIS - 2 or more factors You learned in a previous assignment that unit analysis, or dimensional analysis, is a powerful technique for solving general chemistry problems. Some problems require the use of two or more conversion factors. Since each conversion factor is equal to "one", multiplying by many factors is equivalent to multiplying by "one" many times. This technique can be used to convert a quantity in one set of units, to another, where you do not have a direct relation. You must still include both the number and the unit for each conversion factor. Don't get sloppy about this or you will lose track of what you are doing. Converting from Mass to Number is an example of where more than one conversion factor is necessary: 15.0 grams copper = ? atoms of copper
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Unformatted text preview: grams of Cu 1 mole Cu 6.02 x 10 23 atoms Cu = atoms Cu (number) (unit) (number) (unit) 63.54 grams Cu 1 mole Cu (number) (unit) (number) (unit) There is no direct conversion between grams of copper and number of copper atoms. Here you must first use the atomic mass to convert to moles and then use Avogadro's number to convert to atoms. Note that the units grams Cu "cancel out" in the first conversion, leaving units of moles. Moles then cancel out in the second conversion, leaving units of atoms Cu . The value you are converting FROM always goes on the bottom of the first conversion factor. The value you are converting TO always goes on the top of the last conversion factor. Use two or more conversion factors whenever you do not have a direct relation between units....
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