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Percent Yield and Percent Purity Q: If 5.0 g of potassium metal is burned in air what mass of potassium oxide is expected as a product? What if this experiment was done and only 5.5 g of K2O was produced? Actual Yield: The mass of product that you actually collected/observed Theoretical Yield: The mass of product that you should have obtained (calculated via stoichiometry) Percent yield: The percentage of the maximum amount of product possible that you actually obtained. Practice: a) If 15.5g of Fe(s) are reacted with excess nitric acid, what is the theoretical yield of hydrogen gas? b) What is the percent yield if only 0.473g of H2 were obtained? What are some possible reasons for the theoretical yield not being obtained in a chemical reaction? → Impurities in the reactants → Other unexpected reactions occurring (competing reactions) → Products being converted back into reactants → Loss of material during transfers Percent Purity: Most samples of compounds are not found on their own, they are often mixed together with other compounds and elements. For example, most metals are found in ores which contain the elemental metal along with metal oxides and many other minerals. Percent purity: The percent purity is the percentage of the mass of a sample that is due to a certain element of compound. Example: Iron metal is mined as ores, some of which are magnetite (Fe3O4) and hematite (Fe2O3). If a 50.0g sample of iron ore contains 65.0% Fe, what mass of Fe is actually present in the sample? Example: If a 13.5g sample of sulfur that is 45.0% pure is reacted with excess iron, what mass of iron (II) sulfide would you expect to obtain?
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