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86 Chapter Three Stoichiometry Thus the mass of 1 mole of CaC0 3 (1 mol Ca 2 + plus 1 mol CO/-) is 100.09 g. This is the molar mass. b. The mass of 1 mole of CaC0 3 is 100.09 g. The sample contains nearly 5 moles, or close to 500 g. The exact amount is determined as follows: 100.09 g CaC0 3 4.86 ~ X = 486 g CaC0 3 1~ To find the mass of carbonate ions (CO/-) present in this sample, we must real- ize that 4.86 moles of CaC0 3 contains 4.86 moles of Ca2+ ions and 4.86 moles of CO/- ions. The mass of 1 mole of C0 3 2 - ions is 1 C: 1 X 12.01 = 12.01 g 30: 3 X 16.00 = 48.00 g Mass of 1 mol CO/- = 60.01 g Thus the mass of 4.86 moles of CO/- ions is 60.01 g C0 3 2 - 2- 4.86 ~ X 1111Ql. .-fB{~ = 292 g C0 3 SEE EXERCISES 3.51 THROUGH 3.54 EXAMPLE 3.8 j Isopentyl acetate is released when a bee stings. Isopentyl acetate Oxygen Carbon Hydrogen Isopentyl acetate (C 7 H I4 0 2 ) is the compound responsible for the scent of bananas. A mo- lecular model of isopentyl acetate is shown in the margin below. Interestingly, bees release about 1 ILg (1 X 10-6 g) of this compound when they sting. The resulting
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Unformatted text preview: scent attracts other bees to join the attack. How many molecules of isopentyl acetate are released in a typical bee sting? How many atoms of carbon are present? Solution Since we are given a mass of isopentyl acetate and want to find the number of molecules, we must first compute the molar mass: 7 mol C X 12.01!r = 84.07 g C 14 mol H X l.008!r = 14.11 g H 2 mol 0 X 16.00!r = 32.00 g 0 130.18 g This means that 1 mole of isopentyl acetate (6.022 X 10 23 molecules) has a mass of 130.18 g. To find the number of molecules released in a sting, we must first determine the num-ber of moles of isopentyl acetate in 1 X 10-6 g:-6 1 mol C 7 H 14 2-9 1 X 10 ~ X = 8 X 10 molC 7 H 14 2 130.18~ Since 1 mole is 6.022 X 10 23 units, we can determine the number of molecules: 6.022 X 10 23 molecules _ 8 X 10-9 ~ X = 5 X 10 1 ) molecules 1~...
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This note was uploaded on 12/13/2010 for the course CHEM 2301 taught by Professor Bill during the Spring '10 term at South Texas College.

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