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Clicker #1 You have two beakers on your lab table. Beaker #1 contains g of sulfur and Beaker #2 contains g of arsenic (As). Which beaker contains the greatest number of atoms? Choose the best answer. A) Beaker #1 because one sulfur atom weighs less than one arsenic atom so you need more of the sulfur atoms to fill the beaker. B) Beaker #1 because it contains more moles of sulfur atoms versus the number of moles of arsenic atoms in Beaker #2. C) Beaker #2 because arsenic has a greater mass than sulfur. D) Beaker #2 because it contains more moles of arsenic atoms versus the number of moles of sulfur atoms in Beaker #1. E) Beakers #1 and #2 contain the same number of atoms because there is one mole in each.
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Example How many H2O molecules are contained in 50.0 g of water? How many hydrogen atoms are present in this sample?
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Clicker #2 Does a methane molecule (CH4) consist of more hydrogen or carbon? A) hydrogen B) carbon C) depends
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Clicker #3 What is the percent composition (by mass) of carbon in 2 moles of CH4? A) 2.00% C B) 37.45% C C) 74.9% C D) 149.8% C
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Another Example What is the percent mass of nitrogen in barium nitrate?
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One more… What is the percent mass of oxygen in each? H2O vs. H2O2
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New Example You have some “nitrogen oxide” compound and you want to figure out what it is (both the formula and the name). You know it’s 30.4% nitrogen by mass. NxOy = formula? name?
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Clicker #4 The molecular formula (actual formula) for water is H2O. What is its empirical formula? A) HO½ B) H2O C) H2O2 D) H4O2 E) Cannot be determined without knowing the percent mass of each.
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Consider the problem… If you have equal masses of each compound (H2SO4, C12H22O11, KClO3), which one has the greatest number of oxygen atoms?
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