Key 1.19 JDL (1)

# Key 1.19 JDL (1) - 23 atoms in 1 mole Now we need to...

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Key for Micro Exam 1 Question 19 JDL edit Question 19: A 100 g sample of a material contains 12 grams of an ion of carbon with a charge of -2. How many moles of electrons are found in the carbon ions? Answers: (a) 1 (b) 2.4 x 10 24 (c) 4 (d) 8 (e) 4.8 x 10 24 (f) 6 The question is asking how many moles of electrons are found in 12 g of an ion of carbon with a -2 charge. First of all, recognize that the fact that the sample is 100 g is irrelevant. We are only concerned with the 12 g portion of this sample. Let’s start by converting the 12 g of C to moles of C. If we consult the periodic table we find that the atomic mass of C is 12 g/mol. This is convenient since the two combine to yield 1 mole of C. Now we need to convert moles of C to atoms of C using Avogadro’s number. Avogadro’s number states that there are 6 x 10
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Unformatted text preview: 23 atoms in 1 mole. Now we need to convert atoms of C to electrons. We need to consult the periodic table again in order to observe the atomic number of C. It is 6, so this means that C has 6 protons and also 6 electrons. However, this particular sample of C has a -2 charge which means that each atom has two additional electrons giving each atom a total of 8 electrons. Since the question requests for the answer to be given in moles, we need to convert the electrons back into moles by using Avogadro’s number. This number merely means that there are 6 x 10 23 items in a mole of that item. Here, the item is electrons. This gives us our final answer, answer (d). 12 g C | 1 mol C | 6 x 10 23 atoms of C | 8 electrons | 1 mol electrons = 8 mol electrons | 12 g C | 1 mol C | 1 atom of C | 6 x 10 23 atoms...
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## This document was uploaded on 11/04/2011 for the course CHEM 105 at BYU.

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