Chapter 2
Unit Conversions
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ou may agree with Roger Bacon that mathematics is the easiest of sciences, but many beginning chemistry students would not. Because they have found mathematics challenging, they wish it were not so important for learning chemistry—or for answering so many of the questions that arise in everyday life. They can better relate to Fran Lebowitz’s advice in the second quotation. If you are one of the latter group, it will please you to know that even though there is some algebra in chemistry, this chapter teaches a technique for doing chemical calculations (and many other calculations) without it. Although this technique has several common names, it is called unit analysis in this text. You will be using it throughout the rest of this book, in future chemistry and science courses, and in fact, any time you want to calculate the number of nails you need to build a fence, or the number of rolls of paper you require to cover the kitchen shelves.
2.1 Unit Analysis
2.2 Rounding Off and Significant Figures
2.3 Density and Density Calculations
2.4 Percentage and Percentage Calculations
2.5 A Summary of the Unit Analysis Process
2.6 Temperature Conversions
List the metric units without prefixes and the corresponding abbreviations for length (meter, m), mass (gram, g), and volume (liter, L). (Section 1.4)
State the numbers or fractions represented by the following metric prefixes, and write their abbreviations: giga, mega, kilo, centi, milli, micro, nano, and pico. (Section 1.4)
Given a metric unit, write its abbreviation; given an abbreviation, write the full name of the unit. (Section 1.4)
Describe the relationships between the metric units that do not have prefixes (such as meter, gram, and liter) and units derived from them by the addition of prefixes—for example, 1 km = 103 m. (Section 1.4)
Describe the Celsius, Fahrenheit, and Kelvin scales used to report temperature values. (See Section 1.4)
Given a value derived from a measurement, identify the range of possible values it represents, on the basis of the assumption that its uncertainty is ±1 in the last position reported. (For example, 8.0 mL says the value could be from 7.9 mL to 8.1 mL.) (Section 1.5)
Unit analysis, the technique for doing unit conversions described in this chapter, can be used for a lot more than chemical calculations.
[M]athematics… is the easiest of sciences, a fact which is obvious in that no one’s brain rejects it….
Roger Bacon (c. 1214-c. 1294), English philosopher and scientist
Stand firm in your refusal to remain conscious during algebra. In real life, I assure you, there is no such thing as algebra.
Fran Lebowitz (b. 1951), American journalist
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.
