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General Chemistry

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Question
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Which of the following best represents the total number of ions present in a sample of NaCl weighing 102 g?

A 6.0 x 1023 ions
B 10.5 x 1023 ions
C 12.0 x 1023 ions
D 21 x 1023 ions
Ans. D The sample weighs 56 g. The formula weight of O2 is 32 g/mol. So the number of moles of oxygen present is roughly 1.75. Remember that 1 mol contains Avogadro number of particles. Since 1.75 moles of oxygenis present, there are 1.75 x 6.0 x 1023 molecules of oxygen. Are we done at this point? No! The question asks for the total number of ions present in the sample. Since each oxygenmolecule is composed of oxygen atoms, the total number of atoms in this sample equals 2 x 1.75 x 6.0 x 1023 = 21 x 1023.

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