Challenge Problems

A mixture of NaCl and NaBr has a mass of 2.00 g and contains 0.75 g of Na. What is the mass of NaBr in the mixture  

Three pure compounds form when 1.00 g samples of element X combine with, respectively, 0.472 g, 0.630 g, and 0.789 g of element Z. The first compound has the formula X2Z3. Find the empirical formulas of the other two compounds. 

A mixture of CaC03 and (NH4)2C03 is 61.9% CO3 by mass. Find the mass percent of CaC03 in the mixture. 

A mixture of 50.0 g of S and 1.00 X 10 g of CI2 reacts completely to form S2CI2 and SCI2. Find the mass of S2CI2 formed. 

Because of increasing evidence of damage to the ozone layer, chlorofluorocarbon (CFC) production was banned in 1996. However, there are about 100 million auto air conditioners in operation that stdl use CFC-12 (CF2CI2). These air conditioners are recharged from stockpiled supplies of CFC-12. If each of the 100 milhon automobiles contains 1.1 kg of CFC-12 and leaks 25% of its CFC-12 into the atmosphere per year, how much chlorine, in kg, is added to the atmosphere each year due to auto air conditioners (Assume two significant figures in your calculations.) 

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We begin our discussion of nanocrystals in diis chapter widi die most challenging problem faced in die field die preparation and characterization of nanocrystals. These systems present challenging problems for inorganic and analytical chemists alike, and die success of any nanocrystal syndiesis plays a major role in die furdier quantitative study of nanocrystal properties. Next, we will address die unique size-dependent optical properties of bodi metal and semiconductor nanocrystals. Indeed, it is die striking size-dependent colours of nanocrystals diat first attracted... 

As we should remember now, we distribute the objects into subsets in accordance with some criterion, not having known even the number of subsets themselves. That is why the evaluation of data complexity is still a challenging problem. 

Clearly, the extraction of knowledge on chemical reactions from the information contained in reaction databases (see Section 5.12) is quite a challenging problem. The huge amount of information stored in reaction databases - the larger ones contain several million reactions - renders them quite attractive for knowledge extraction. However, only a few attempts have been made to extract knowledge automatically. 

Before concluding this section it should be emphasi/cd that knowledge extraction from reaction databases is still a challenging problem having many important applications. There is still room for new approaches to this task, Furthermore, groat efforts should be made to improve the depth of information stored in reaction databases. With the introduction of electronic lab journals, the primary information on a chemical reaction gained in the laboratoiy becomes directly available. 

A particularly challenging problem is the understanding and modeling of biochemical and metabolic reactions, and even more so of metabolic reaction networks. Much work will go into this field in the next few years. 

Problems in Strategy Our discussion on strategy was hmited to the more straightforward aspects. This section has some challenging problems without worked answers. These are more difficult than the revision problems. 

This is a very challenging problem indeed. You may find some solutions by setting up two substituents on tlie carbon atom. For example, how about a substituted Wittig reagent ... 

A more challenging problem is to find the pH of a solution prepared from a polyprotic acid or one of its conjugate species. As an example, we will use the amino acid alanine whose structure and acid dissociation constants are shown in Figure 6.11. 

This example demonstrates the most challenging problem of flavor chemistry, ie, each flavor problem may require its own analytical approach however, a sensory analysis is always required. The remaining unknown odorants demand the most sensitive and selective techniques, and methods of concentration and isolation that preserve the sensory properties of complex and often dehcate flavors. Furthermore, some of the subtle odors in one system will be first identified in very different systems, like o-amino acetophenone in weasels and fox grapes. 

Regioselective hydrolysis of diesters is a challenging problem ia synthetic chemistry because the side reactions always reduce the yield of desired product. Some Upases are well suited to perform this task. Lipase OF-360 (Meito Sangyo) hydrolyzes diester (55) ia 74% theoretical yield and 93% ee (70). Lipase from Pseudomonas cepacia suspended ia diisopropyl ether saturated with water hydrolyzes triester (56) with a remarkable efficiency and regio- and stereoselectivity (71). 

As the complete genomes of more and more species are sequenced, the determination of the function of previously unidentified open reading frames is becoming an increasing and challenging problem. The possibility of... 

The study on ring transformations of heterocycles is an attractive subject of research for many years. This great interest is due to the fact that these reactions are usually easily performed and that by these ring transformations heterocycles can be synthesized which are otherwise difficult to obtain. Moreover, unravelling the course of the ring transformation has always been a challenging problem and has attracted the interest of many chemists it requires studies on substituent and solvent effects, labeling and NMR studies, kinetic studies and quantum chemical calculations. In the course of... 

This manual includes complete solutions to all end-of-chapter Questions and Problems answered in Appendix 6, including the Challenge Problems. The author includes references to textbook sections and tables to help guide students to use the problem-solving techniques employed by the authors. Selected solutions from each chapter, identified by the web icon, are on the student companion site at academicxengagexom/chemistry/masterton. 

The section of challenge problems presents problems that may require extra skill and/or insight and effort. They are all answered in Appendix 6. 

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