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Key 1.15 JDL

# Key 1.15 JDL - convert the number of moles of Si to atoms...

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Key for Micro Exam 1 Question 15 JDL edit Question 15: A 56 g sample of rock from the moon was found to contain 25% Si by weight. How many protons are contained in the silicon atoms in this sample? Answers: (a) 4.2 x 10 24 (b) 8.1 x 10 24 (c) 3.9 x 10 23 (d) 1.6 x 10 25 (e) 3 x 10 23 (f) 6 x 10 23 (g) None, there are no protons on the moon. First, divide the 56 g sample of rock by 4 in order to focus on the 25% portion that is Si: 56/4 = 14 g of Si. Now consult a periodic table to obtain the atomic mass of Si (28 g/mol). Now we can
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Unformatted text preview: convert the number of moles of Si to atoms of Si by using Avogadro’s number, which states that there are 6 x 10 23 atoms in one mole. Finally we must consult the periodic table again to find the atomic number of Si (14) in order to convert the atoms to protons—the atomic number is the number of protons in each atom. 14 g Si | 1 mol Si | 6 x 10 23 atoms of Si | 14 protons = 42 x 10 23 protons = 4.2 x 10 24 protons | 28 g Si | 1 mol Si | 1 atom Si...
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