General, Organic, and Biological Chemistry

Fourth EditionKaren Timberlake

1.9Problem Solving

Chapter 1Chemistry and Measurements

© 2013 Pearson Education, Inc.Lectures

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There are 4 steps to solving problems with conversion

factors.

Guide to Problem Solving Using Conversion Factors

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If a person weighs 164 lb, what is the body mass inkilograms?

Step 1 State the given and needed quantities. Analyze the Problem

Step 2 Write a plan to convert the given unit to the needed unit.

lb US–Metric kilograms Factor

Steps to Solving the Problem

Given Need

164 lb kilograms

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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.

Steps to Solving the Problem

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Learning Check

How many minutes are 2.5 h?

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Solution

How many minutes are 2.5 h?

Step 1 State the given and needed quantities.

Analyze the Problem.

Step 2 Write a plan to convert the given unit to the needed unit.

Given Need

2.5 h minutes

hour minutestimefactor

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Solution

How many minutes are 2.5 h?

Step 3 State the equalities and conversion factors.

Step 4 Set up problem to cancel units and calculate answer.

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A rattlesnake is 2.44 m long. How many centimeters long is the snake?

A. 2440 cm

B. 244 cm

C. 24.4 cm

Learning Check

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A rattlesnake is 2.44 m long. How many centimeterslong is the snake?

Step 1 Analyze the Problem.

Step 2 Write a plan to convert the given unit to the needed unit. meters metric centimeters

conversion

Solution

Given Need

2.44 m centimeters

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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

3 SF 3 SFExactAnswer: B

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Often, two or more conversion factors are required to obtain the unit needed for the answer.

Unit 1 Unit 2 Unit 3

Additional conversion factors are placed in the setupto cancel each preceding unit.

Using Two or More Factors

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How many minutes are in 1.6 days?

Step 1 State the given and needed quantities.

Analyze the Problem.

Step 2 Write a plan to convert the given unit to the needed unit.

days time time min factor 1 factor 2

Example: Problem Solving

Given Need

1.6 days minutes

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How many minutes are in 1.6 days?

Step 3 State the equalities and conversion factors.

Step 4 Set up problem to cancel units and calculate answer.

Example: Problem Solving

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Learning Check

An injured person loses 0.300 pints of blood. How many milliliters of blood would that be?

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Solution

An injured person loses 0.300 pints of blood. How many milliliters of blood would that be?

Step 1 State the given and needed quantities. Analyze the Problem.

Step 2 Write a plan to convert the given unit to the needed unit.

pints factor 1 factor 2 milliliters

Given Need

0.300 pints milliliters

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SolutionAn injured person loses 0.300 pints of blood. How many milliliters of blood would that be?

Step 3 State the equalities and conversion factors.

Step 4 Set up problem to cancel units and calculate answer.