General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 2.6 Problem Solving Using Unit Conversion Exercising regularly helps reduce body fat. Learning Goal Use conversion factors to change from one unit to another.

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Problem Solving Using Unit Conversion The process of problem solving in chemistry often requires one or more conversion factors to change a given unit to the needed unit. Problem solving in chemistry requires identification of the given quantity units. determination of the units needed. identification of conversion factors that connect the given and needed units. Core Chemistry Skill Using Conversion Factors

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Problem Solving Using Unit Conversion Steps for solving problems that contain unit conversions include the following:

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solving Problems Using Unit Conversion Example: If a person weighs 164 lb, what is the body mass in kilograms? STEP 1 State the given and needed quantities. STEP 2 Write a plan to convert the given unit to the needed unit. poundskilograms

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solving Problems Using Unit Conversion Example: If a person weighs 164 lb, what is the body mass in kilograms? STEP 3 State the equalities and conversion factors. STEP 4 Set up the problem to cancel units and calculate the answer.

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check A rattlesnake is 2.44-m long. How many centimeters long is the snake?

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution A rattlesnake is 2.44-m long. How many centimeters long is the snake? STEP 1 State the given and needed quantities. STEP 2 Write a plan to convert the given unit to the needed unit. meters centimeters ANALYZE GIVEN NEED THE PROBLEM 2.44 m centimeters ANALYZE GIVEN NEED THE PROBLEM 2.44 m centimeters Metric Factor Metric Factor

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. A rattlesnake is 2.44-m long. How many centimeters long is the snake? STEP 3 State the equalities and conversion factors. STEP 4 Set up the problem to cancel units and calculate the answer. Solution

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Using Two or More Conversion Factors In problem solving, two or more conversion factors are often needed to complete the change of units. in setting up these problems, one factor follows the other. each factor is arranged to cancel the preceding unit until the needed unit is obtained.

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Using Two or More Conversion Factors Example: A doctor’s order prescribed a dosage of mg of Synthroid. If tablets contain 75 mcg of Synthroid, how many tablets are required to provide the prescribed medication? STEP 1 State the given and needed quantities. STEP 2 Write a plan to convert the given unit to the needed unit. milligrams micrograms ANALYZE GIVEN NEED THE PROBLEM mg Synthroid number of tablets ANALYZE GIVEN NEED THE PROBLEM mg Synthroid number of tablets Metric Factor Metric Factor Clinical Factor Clinical Factor number of tablets

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Example: A doctor’s order prescribed a dosage of mg of Synthroid. If tablets contain 75 mcg of Synthroid, how many tablets are required to provide the prescribed medication? STEP 3 State the equalities and conversion factors. STEP 4 Set up the problem to cancel units and calculate the answer. Using Two or More Conversion Factors

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check How many minutes are in 1.4 days?

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution How many minutes are in 1.4 days? STEP 1 State the given and needed quantities. STEP 2 Write a plan to convert the given unit to the needed unit. days hours minutes ANALYZE GIVEN NEED THE PROBLEM 1.4 days minutes ANALYZE GIVEN NEED THE PROBLEM 1.4 days minutes Time Factor Time Factor Time Factor Time Factor

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. How many minutes are in 1.4 days? STEP 3 State the equalities and conversion factors. STEP 4 Set up the problem to cancel units and calculate the answer. Solution

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7.5 kilometers?

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7.5 kilometers? STEP 1 State the given and needed quantities. STEP 2 Write a plan to convert the given unit to the needed unit. kilometers meters minutes Metric Factor Metric Factor Speed Factor Speed Factor ANALYZE GIVEN NEED THE PROBLEM 65 meters/min minutes 7.5 kilometers ANALYZE GIVEN NEED THE PROBLEM 65 meters/min minutes 7.5 kilometers

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. If your pace on a treadmill is 65 meters per minute, how many minutes will it take for you to walk a distance of 7.5 kilometers? STEP 3 State the equalities and conversion factors. STEP 4 Set up the problem to cancel units and calculate the answer. Solution

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Toxicology A basic concept of toxicology is the statement of Paracelsus that the dose is the difference between a poison and a cure. To evaluate the level of danger from various substances, natural or synthetic, a risk assessment is made by exposing laboratory animals to the substances and monitoring the health effects. One measure of toxicity is the LD 50, or lethal dose, which is the concentration of the substance that causes death in 50% of the test animals.

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Toxicology A dosage is typically measured in milligrams per kilogram (mg/kg) of body mass. micrograms per kilogram (mcg/kg) of body mass. The LD 50 of caffeine is 192 mg/kg.

General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Toxicology Other evaluations must be made, but it is easy to compare LD 50 values. Some LD 50 values for substances tested in rats are listed in order of increasing toxicity. Parathion, a pesticide, with an LD 50 of 3 mg/kg, would be highly toxic.