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Unformatted text preview: C HAPTER 9 C HEMICAL C ALCULATIONS AND C HEMICAL F ORMULAS 329 n order to explore and make use of the seemingly limitless changes that matter can undergo, chemists and chemistry students often need to answer questions that begin with, How much ? The research chemist who is developing a new cancer drug wants to know, How much radioactive boron10 do I need to make 5 g of the drug? At a chemical plant where the fat substitute Olestra is manufactured from white sugar and vegetable oil, a business manager asks a chemist, How much sucrose and cottonseed oil should I order if we need to produce 500 Mg of Olestra per day? In an experiment for a chemistry course you are taking, you might be asked, How much magnesium oxide can be formed from the reaction of your measured mass of magnesium with the oxygen in the air? This chapter and the chapters that follow provide you with the tools necessary to answer these questions and many others like them. 9.1 A Typical Problem 9.2 Relating Moles to Number of Particles 9.3 Molar Mass and Chemical Compounds 9.4 Relationships Between Masses of Elements and Compounds 9.5 Determination of Empirical and Molecular Formulas Write or recognize the definition of isotope. (Section 2.4) Describe the general structure of molecular and ionic compounds. (Sections 3.3 and 3.5) Convert between the names of compounds and their chemical formulas. (Section 5.3) Report the answers to calculations to the correct number of significant figures. (Section 8.2) Use percentages as conversion factors. (Section 8.4) Make unit conversions. (Section 8.5) All of these people ask questions that begin, How much...? Review Skills The presentation of information in this chapter assumes that you can already perform the tasks listed below. You can test your readiness to proceed by answering the Review Questions at the end of the chapter. This might also be a good time to read the Chapter Objectives, which precede the Review Questions. 9.1 A Typical Problem 1 To avoid potential confusion, the states( s ), ( l ), ( g ), and ( aq )are not mentioned in equations describing industrial reactions in Chapters 9 and 10. Many industrial reactions are run at temperatures and pressures under which the states of substances differ from what would be expected at room temperatures and pressures. For example, the Ca 3 (PO 4 ) 2 in the first equation on this page is a solid under normal conditions but a liquid at 2000 C; SiO 2 is also solid under normal conditions but a glass (or semisolid) at 2000 C. Imagine you are a chemist at a company that makes phosphoric acid, H 3 PO 4 , for use in the production of fertilizers, detergents, and pharmaceuticals. The goal for your department is to produce 84.0% H 3 PO 4 (and 16.0% water) in the last stage of a three step process known as the furnace method. (We will be using the furnace method as a source of practical examples throughout this chapter and in Chapter 10.) The first step in the furnace method is the extraction of phosphorus from phosphate...
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- Fall '06