Ch400Ch3LN5 - Chem 400 Chapter 3 Lecture Notes Part 5...

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Chem 400 Chapter 3 Lecture Notes Part 5 Finding %-Composition of a Compound • Say we have some methanol (CH 3 OH). What’s the %-composition by mass of methanol? • Just like finding the %-lefties in the class, it’s basically just part over whole. • So you need to find the mass of each element in the compound and the overall mass of the compound. So you do need to know the chemical formula (either empirical or molecular) for the compound. • To make the math easier, you just assume you have exactly 1 mole of the compound. So you have a molar mass of the compound overall. • Many times, the problem just asks for the %-composition of one element or the %-composition of an ion or the %-water in a hydrate: • What’s the %-P in phosphoric acid? • What’s the %-water in magnesium sulfate heptahydrate? Finding the Empirical Formula and Molecular Formula from the %-Composition • If you synthesize a compound in the lab, you obviously want to identify it. • So you want to find its chemical formula.
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Ch400Ch3LN5 - Chem 400 Chapter 3 Lecture Notes Part 5...

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