Lec-08-Chap-03-3 - CHE 131 Lecture 8, 2/8/2006 Ionic...

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CHE 131 Lecture 8, 2/8/2006 Ionic Compounds and Compositions Lecture eight (Chapter three) Benjamin S. Hsiao Department of Chemistry Stony Brook University Simplest (Empirical) Formula • formula describing a substance based on the smallest set of subscripts EXAMPLE: Phosphorus burns in air to produce a white compound that is 43.7% P and 56.3% O by mass. What is the empirical formula of the compound? % 43.7% P 56.3% O Relative Number of Atoms (%/gaw) 43.7/30.97 = 1.41 56.3/15.9994 = 3.52 Divide by Smaller 1.41/1.41 = 1.00 3.52/1.41 = 2.50 Multiply by Integer 2 × 1.00 2 2 × 2.50 5 Empirical Formula P 2 O 5 EXAMPLE: The burning of fossil fuels in air produces a brown-colored gas, a major air pollutant, that contains 2.34 g of N and 5.34 g of O . What is the empirical formula of the compound? 2.34 %N = × 100 = 30.5% N 2.34 + 5.34 5.34 %O = × 100 = 69.5% O 2.34 + 5.34
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CHE 131 Lecture 8, 2/8/2006 EXAMPLE: The burning of fossil fuels in air produces a brown-colored gas, a major air pollutant, that contains 2.34 g of N and 5.34 g of O . What is the empirical formula of the compound? %N = 30.5% N %O = 69.5% O Relative # Atoms Multiply % (%/gaw) Divide by Smaller by Integer N 30.5 30.5/14.0067 = 2.18 2.18/2.18 = 1.00 1 × 1.00 1 O 69.5 69.5/15.9994 = 4.34 4.34/2.18 = 1.99 1 × 1.99 2 Empirical Formula N O 2 Molecular Formula • the exact proportions of the elements that
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Lec-08-Chap-03-3 - CHE 131 Lecture 8, 2/8/2006 Ionic...

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