1. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 2.5 Writing Conversion Factors In the United States, the contents of many packaged foods are listed in both U.S. and metric units. Learning Goal Write a conversion factor for two units that describe the same quantity.

2. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Equalities use two different units to describe the same measured amount. are written for relationships between units of the metric system, U.S. units, or between metric and U.S. units. For example, 1 m = 1000 mm (10 3 mm) 1 lb = 16 oz 2.20 lb = 1 kg Core Chemistry Skill Writing Conversion Factors from Equalities

3. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Equalities: Conversion Factors Any equality can be written as conversion factors. Conversion Factors for the Equality 60 min = 1 h Conversion Factors for the Metric Equality 1 m = 100 cm

4. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Equalities: Conversion Factors and SF The numbers in any equality between two metric units between two U.S. system units are obtained by definition and are, therefore, exact numbers. a definition are exact and are not used to determine significant figures. an equality between metric and U.S. units contain one number obtained by measurement and count toward the significant figures. Exception: The equality 1 in. = 2.54 cm has been defined as an exact relationship. Therefore, 2.54 is an exact number.

5. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Some Common Equalities

6. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Metric Conversion Factors We can write metric conversion factors. Both are proper conversion factors for the relationship; on is just the inverse of the other.

7. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Metric–U.S. System Conversion Factors We can write metric–U.S. system conversion factors. In the United States, the contents of many packaged foods are listed in both U.S. and metric units.

8. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Write conversion factors from the equality for each of the following: A. liters and milliliters B. meters and inches C. meters and kilometers

9. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Write conversion factors from the equality for each of the following: A. B. C.

10. Equalities and Conversion Factors Within a Problem An equality may also be stated within a problem that applies only to that problem. The car was traveling at a speed of 85 km/h. One tablet contains 500 mg of vitamin C. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

11. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Equalities stated within dosage problems for medication can also be written as conversion factors. Keflex (Cephalexin), an antibiotic used for respiratory and ear infections, is available in 250-mg capsules. Conversion Factors: Dosage Problems

12. Conversion Factors: Percentage, ppm, ppb A percentage (%) is written as a conversion factor by choosing a unit and expressing the numerical relationship of the parts of this unit to 100 parts of the whole. A person might have 18% body fat by mass. To indicate very small ratios, we use parts per million (ppm) and parts per billion (ppb). General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.

13. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Write the equality and its corresponding conversion factors. Identify each number as exact, or give its significant figures in the following statement: Salmon contains 1.9% omega-3 fatty acids.

14. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Write the equality and its corresponding conversion factors. Identify each number as exact, or give its significant figures in the following statement: Salmon contains 1.9% omega-3 fatty acids. ExactTwo SFs

15. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Write the equality and conversion factor for each of the following: A. Meters and centimeters (length) B. Jewelry that contains 18% gold (percentage) C. One gallon of gas is $3.40.

16. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Write the equality and conversion factor for each of the following: A. Meters and centimeters B. Jewelry that contains 18% gold C. One gallon of gas is $3.40.