STRATEGIES IN CHEMISTRY Problem Solving

Let s examine this question using the problem-solving steps in the accompanying Strategies in Chemistry Problem Solving essay. 

Analyze We are given a chemical formula and asked to calculate the percentage by mass of each element. 

Plan We use Equation 3.10, obtaining our atomic weights from a periodic table. We know the denominator in Equation 3.10, the formula weight of C12H22O11, from Sample Exercise 3.5. We must use that value in three calculations, one for each element 

Even the smallest samples we deal with in the laboratory contain enormous numbers of atoms, ions, or molecules. For example, a teaspoon of water (about 5 mL) contains 2 X 10 water molecules, a number so large it almost defies comprehension. Chemists therefore have devised a counting unit for describing such large numbers of atoms or molecules. 

In everyday life we use such familiar counting units as dozen (12 objects) and gross (144 objects). In chemistry the counting unit for numbers of atoms, ions, or molecules in a laboratory-size sample is the mole, abbreviated mol. One mole is the amount of matter that contains as many objects (atoms, molecules, or diatever other objects we are considering) as the number of atoms in exactly 12 g of isotopicaUy pure C. From experiments, scientists have determined this number to be 6.0221421 X 10, diich we will usually round to 6.02 X 10. Scientists call this value Avogadro s number, N, in honor 

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Strategies in Chemistry teach ways to analyze information and oiganize thoughts, helping to improve your problem-solving and critical-thinking abilities. 

We provide a valuable overview of each chapter under the What s Ahead banner. Concept links (cro) continue to provide easy-to-see cross-references to pertinent material covered earlier in the text. The essays titled Strategies in Chemistry, which provide advice to students on problem solving cuid thinking like a chemist, continue to be eui importeuit feature. For example, the new Strategies in Chemistry essay at the end of Chapter 3 introduces the new Design an Experiment feature cuid provides a worked out example as guidance. 

Chemistry is full of calculations. Our basic goal is to help you develop the knowledge and strategies you need to solve these problems. In this chapter, you will review the Metric system and basic problem solving techniques, such as the Unit Conversion Method. Your textbook or instructor may call this problem solving method by a different name, such as the Factor-Label Method and Dimensional Analysis. Check with your instructor or textbook as to for which SI (Metric) prefixes and SI-English relationships will you be responsible. Finally, be familiar with the operation of your calculator. (A scientific calculator will be the best for chemistry purposes.) Be sure that you can correctly enter a number in scientific notation. It would also help if you set your calculator to display in scientific notation. Refer to your calculator s manual for information about your specific brand and model. Chemistry is not a spectator sport, so you will need to Practice, Practice, Practice. 

Solved Problems in Chemistry is written by David E. Goldberg. This Schaum s solved problem manual provides 3000 solved problems. It provides problem-solving strategies and helpful hints in studying. 

Niaz, M. (1995). Cognitive conflict as a teaching strategy in solving chemistry problems A dialectic-constructivist perspective. Journal of Research in Science Teaching, 32, 959-970. 

Practice Problems Students need ample opportunities to practice and apply their new found strategies for solving organic chemistry problems. We ve added to our rich array of in-text Practice Problems to provide students with even more opportunities to check their progress as they study If they can work the practice problem, they should move on. If not, they should review the preceding presentation. 

Example Problem 1.4 shows how this type of manipulation fits into a problem solving strategy with non-chemistry examples before we look at it in a chemistry context. 

Calculations in chemistry use ratios very often. Example Problem 1.6 also shows how they are used in combinations. Learning how to carry out these sequential manipulations will be a key part of solving many of the problems we encounter in chemistry. One guide that often helps to determine how to construct the appropriate ratio is to note the units used. For example, the equality between 1000 mL and 1 L leads to two ways to express the ratio, 1000 mL/1 L or 1 L/1000 mL. Which ratio did we need Because we started with liters, we required the former ratio, with 1 L in the denominator. We will often include discussions about the ratios we form in the strategy part of the example problems. 

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