A Systematic Approach to Solving Chemistry Problems

The approach we use in this text provides a systematic way to work through a problem. It emphasizes reasoning, not memorizing, and is based on a very simple idea plan how to solve the problem before you go on to solve it, and then check your answer. Try to develop a similar approach on homework and exams. In general, the sample problems consist of several parts  

Problem. This part states all the information you need to solve the problem (usually framed in some interesting context). 

The overall solution is broken up into two parts, plan and solution, to make a point think about how to solve the problem before juggling numbers. There is often more than one way to solve a problem, and the plan shown in a given problem is just one possibility develop a plan that suits you best. The plan will 

Solution. In this part, the steps appear in the same order as in the plan. 

In most cases, a quick check is provided to see if the results make sense Are the units correct Does the answer seem to be the right size Did the change occur in the expected direction Is it reasonable chemically We often do a rough calculation to see if the answer is in the same ballpark as the calculated result, just to make sure we didn t make a large error. Here s a typical ballpark calculation. You are at the music store and buy three CDs at 14.97 each. With a 5% sales tax, the bill comes to 47.16. In your mind, you quickly check that 3 times approximately 15 is 45, and, given the sales tax, the cost should be a bit more. So, the amount of the bill is in the right ballpark. Always check your answers, especially in a multipart problem, where an error in an early step can affect all later steps. 

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Units and Conversion Factors in Calculations 10 A Systematic Approach to Solving Chemistry Problems 12... 

Generally, we can calculate the hydrogen ion concentration or pH of an acid solution at equilibrium, given the initial concentration of the acid and its value. Alternatively, if we know the pH of a weak acid solution and its initial concentration, we can determine its K. The basic approach for solving these problems, which deal with equilibrium concentrations, is the same one outlined in Chapter 14. However, because acid ionization represents a major category of chemical equilibrium in aqueous solution, we will develop a systematic procedure for solving this type of problem that will also help us to understand the chemistry involved. 

However, as new approaches or new theories are developed, the solution of problems insoluble within the framework of traditional concepts is accompanied by appearance of new problems and enigmas. This approach is not an exception. In particular, the mechanism of the transfer of the condensation energy of the low-volatility product to the reactant and the effect of the S3mi-metry of the reactant crystal-lattice on the composition of the gaseous decomposition products remain unclear. To solve these problems on the basis of the new mechanistic and kinetic concepts discussed in this book, it would be appropriate to use the experience accumulated in solid-state physical chemistry and in crystal chemistry. The systematic differences between the enthalpies measured by the third-law method and those measured by the second-law and Arrhenius plot methods undoubtedly deserves a more thorough study. This problem is especially important for successful application to reactions involving the formation of solid products. 

Questions like these were raised explicitly and systematically in 1812 by Berzelius, and a few years later by the French chemist Michel Eugene Chevreul (we will discuss their approaches later in the chapter). As Berzelius pointed out shortly afterward, a solution for these problems could not be expected from quantitative elemental analysis alone. In their attempts to solve taxonomic problems, both Berzelius and Chevreul pointed to the limits of quantitative elemental analysis and the theoretical underpinnings of the Lavoisierian analytical program for plant and animal chemistry-limits that some twenty years earlier had been invisible. 

Emil Ott was a firm believer in the team approach to research and he used this organization to solve an enormous number of industrial problems for Hercules. His approach to science was systematic and comprehensive. He adopted a complete structural description, like Haworth. He considered the detailed chemical analysis of his macromolecules. If the chemistry was wrong, the structure was wrong He was an expert in X-ray analysis. The unit cell of crystalline cellulose can be constructed in two different ways, with two cellobiose units. Hydrogen bonding plays an important role in crystalline cellulose. 

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