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Scan_Doc0091 - 3.4 Molar Mass 85 molecules we need a...

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EXAMPLE 3.6 Juglone 3.4 Molar Mass 85 molecules, we need a special name for the fundamental unit of these materials. Instead of molecule, we use the term formula unit. Thus CaC0 3 is the formula unit for calcium carbonate, and NaCl is the formula unit for sodium chloride. Juglone, a dye known for centuries, is produced from the husks of black walnuts. It is also a natural herbicide (weed killer) that kills off competitive plants around the black walnut tree but does not affect grass and other noncompetitive plants. The formula forjuglone isCjQH 6 0 3 a. Calculate the molar mass of juglone. b. A sample of 1.56 X 10- 2 g of pure juglone was extracted from black walnut husks. How many moles of juglone does this sample represent? Solution a. The molar mass is obtained by summing the masses of the component atoms. In 1 mole ofjuglone there are 10moles of carbon atoms, 6moles ofhydrogen atoms, and 3moles of oxygen atoms: 10C: 10 X 12.01 g = 120.1 g 6 H: 6 X 1.008 g = 6.048 g 3 0: 3 X 16.00 g = 48.00 g Mass of 1mol C lO H 6 0 3 = 174.1 g The mass of 1mole of juglone is 174.1 g, which is the molar mass. b. The mass of 1mole of this compound is 174.1 g; thus 1.56
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