Solving Chemical Problems

An experiment typically contains at least two variables, quantities that can have more than a single value. A well-designed experiment is controlled in that it measures the effect of one variable on another while keeping all others constant. For experimental results to be accepted, they must be reproducible, not only by the person who designed the experiment, but also by others. Both skill and creativity play a part in experimental design. 

In an informal way, we often use a scientific approach in daily life. Consider this familiar scenario. While listening to an FM broadcast on your stereo system, you notice the sound is garbled (observation) and assume it is caused by poor reception (hypothesis). To isolate this variable, you play a CD (experiment) the sound is still garbled. If the problem is not poor reception, perhaps the speakers are at fault (new hypothesis). To isolate this variable, you play the CD and listen with headphones (experiment) the sound is clear. You conclude that the speakers need to be repaired (model). The repair shop says the speakers check out fine (new observation), but the power amplifier may be at fault (new hypothesis). Replacing a transistor in the amplifier corrects the garbled sound (new experiment), so the power amplifier was the problem (revised model). Approaching a problem scientifically is a common practice, even if you re not aware of it. 

The scientific method is not a rigid sequence of steps, but rather a dynamic process designed to expiain and predict reai phenomena. Observations (sometimes expressed as natural laws) lead to hypotheses about how or why something occurs. Hypotheses are tested in controlled experiments and adjusted if necessary. If all the data collected support a hypothesis, a model (theory) can be developed to explain the observations. A good model is useful in predicting related phenomena but must be refined if conflicting data appear. 

In many ways, learning chemistry is learning how to solve chemistry problems, not only those in exams or homework, but also more complex ones in professional life and society. In this section, we discuss the problem-solving approach. Most problems include calculations, so let s first go over some important ideas about measured quantities. 

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This short book is intended for students who lack confidence and/or competency in the essential mathematical skills necessary to survive in general chemistry. Each chapter focuses on a specific type of skill and has worked-out examples to show how these skills translate to chemical problem solving. 

Motes occupy the centrai position of this flowchart because the mote is the unit that chemists use in almost all chemical calculations. When you set out to solve a chemical problem, first interpret the question on the atomic/molecular level. The second part of chemical problem solving often involves quantitative calculations, which usually require working with moles. 

How does this understanding of molecular mechanisms of nitrosamlne formation help us solve the practical problem of controlling any contamination associated with the production, storage, or use of pesticides Let us look at two excellent examples of relevant chemical problem-solving. 

Too much caffeine is harmful for many people, and even small amounts cannot be tolerated by some unlucky individuals. How much caffeine is in a chocolate bar How does that amount compare with the quantity in coffee or soft drinks At Bates College in Maine, Professor Tom Wenzel teaches his students chemical problem solving through questions such as these.4 But, how do you measure the caffeine content of a chocolate bar ... 

One common algebraic equation that is often applied in chemical problem solving is... 

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