Scan_Doc0089 - The number of atoms in 10.0 g (0.371 mol) of...

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3.3 The Mole 83 EXAMPLE 3.3 (left) Pure aluminum. (right) Aluminum alloys are used for many high-quality bicycle components, such as this chain wheel. EXAMPLE 3.4 Always check to see if your answer is sensible. Paying careful attention to units and making sure the answer is reasonable can help you detect an inverted conversion factor or a number that was incorrectly entered in your calculator. Aluminum (AI) is a metal with a high strength-to-mass ratio and a high resistance to cor- rosion; thus it is often used for structural purposes. Compute both the number of moles of atoms and the number of atoms in a 1O.0-g sample of aluminum. Solution The mass of 1 mole (6.022 X 10 23 atoms) of aluminum is 26.98 g. The sample we are considering has a mass of 10.0 g. Since the mass is less than 26.98 g, this sample con- tains less than 1 mole of aluminum atoms. We can calculate the number of moles of alu- minum atoms in 10.0 g as follows: 1 mol Al 10.0 g.-M X 26.98 g.-M = 0.371 mol Al atoms
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Unformatted text preview: The number of atoms in 10.0 g (0.371 mol) of aluminum is 6.022 X 10 23 atoms 0.371 mel--Pd X 1 mel--Pd = 2.23 X 10 23 atoms Reality Check: One mole of Al has a mass of 26.98 g and contains 6.022 X 1023atoms. Our sample is 10.0 g, which is roughly 1/3 of 26.98. Thus the calculated amount should be on the order of 1/3 of 6 X 10 23 ,which it is. SEE EXERCISE 3.42 A silicon chip used in an integrated circuit of a microcomputer has a mass of 5.68 mg. How many silicon (Si) atoms are present in the chip? Solution The strategy for doing this problem is to convert from milligrams of silicon to grams of silicon, then to moles of silicon, and finally to atoms of silicon: 1 Si 5.68 mg-st X g = 5.68 X 10-3 g Si 1000 mg-st 1 mol Si 5.68 X 10-3 g--8t X = 2.02 X 10-4 mol Si 28.09 g--8t 6.022 X 10 23 atoms 10-4 mel-8t X = 1.22 X 10 20 atoms 1 mel-8t 2.02 X...
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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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