3.3
Lesson 3.3 Solving Conversion Problems
Objectives
●
3.3.1 Explain what happens when a measurement is
multiplied by a conversion factor.
●
3.3.2 Describe the kinds of problems that can be easily
solved using dimensional analysis.
Lesson Links
Ch. 3 Core TR: Section 3 Review
3.3 Chemistry Tutorial: Using Dimensional Analysis
3.3 Lesson Overview (PowerPoint file)
3.3 Chemistry Tutorial: Using Density as a Conversion Factor
3.3 Kinetic Art: Conversion Factors
Chapter 3 Online Student Edition
Study WB Chapter 3 Lesson 3
Overview/Materials
Pacing
Overview
Standard
In this lesson you will cover how to use conversion factors and
dimensional analysis to solve problems in chemistry.
Classroom Materials
Conversion Factors: copies of a recipe, lists of equivalents and
conversions among the following measurements: teaspoon, tablespoon, 1
/4 cup, 1/2 cup, and 1 cup
Dimensional Analysis: Internet access or copies of media guides
containing vital statistics, such as heights and weights of players on a
sports team (These guides are available from local sports franchises.)
Standard
There are no items.
Chemistry & You
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2
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1
Description
Engage
Resources
Content
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Chapter 3 Online Student
Edition
Have students examine the Chemistry &
You feature on p. 84.
Ask Has anyone ever noticed a chart or
table in a bank or in the newspaper relating
the values of foreign currency to the U.S.
dollar? (yes or no) Explain that these tables
are called currency conversion tables.
These are the daily values that allow people
to relate one currency to another.
Ask How could you know for certain which
amount of money is worth more—75 euros
or 75 British pounds? (Convert these values
to a familiar currency—U.S. dollars.)
Activate Prior Knowledge
Description
Resources
Pacing
Resources
Pacing
Engage
Provide various types of measuring devices
to the class. Tell students to select one
device and record the length of their shoe.
Then ask them to create a chart and record
the length of their shoe in inches, feet, yards,
millimeters, centimeters, and meters. As
a class, discuss how students determined
the measurements. Begin a list of
conversion factors on the word wall.
Conversion Factors
Description
Explain
Have students inspect Figure 3.12.
Emphasize that a conversion factor relates
two equivalent measurements.
Ask What two parts does every
measurement have? (a number and a unit)
Point out that if this is so, then every
conversion factor must contain two numbers
and two units so that one number and its
unit equal another number and its unit.
Have students complete the 3.3 Kinetic Art:
Conversion Factors activity on
PearsonChem.com.
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Content
3.3 Kinetic Art: Conversion
Factors
Content
Figure 3.12
Conversion Factors
Description
Resources
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Resources
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Extend
The conversion of chemical units is similar
to the exchange of currency. Americans who
travel outside the United States must
exchange U.S. dollars for foreign currency
at a given rate of exchange. These
exchange rates vary from day to day. The
daily exchange rates affect all international
monetary transactions. Each time one type
of money is exchanged for another, the
current exchange rate serves as a
conversion factor. International currency
traders keep track of exchange rates 24
hours a day through a linked computer
network. Challenge students to choose a
country to which they would like to travel.
Have them research the exchange rate
and then estimate how much money they
would need, both in American dollars and
the foreign currency, to travel for a week in
that country. They might include things like
airfare, hotel costs, food, and entertainment.
Conversion Factors
Description
Explore
Use a short class activity to allow students
to use dimensional analysis to convert
common units.
Distribute copies of a recipe and a list of
conversion factors to pairs of students.
Explain that they must rewrite the recipe so
that it can feed six times the number of
serving sizes suggested by the recipe. Point
out that it would be tedious to have to
measure out a particular ingredient (pick
out one) in teaspoons or tablespoons six
times, so students must rewrite the recipe in
appropriately larger units. After students
have rewritten the recipe, have student
pairs exchange and compare recipes.
Materials: copies of a recipe, lists of
equivalents and conversions among the
following measurements: teaspoon,
tablespoon, 1/4 cup, 1/2 cup, and 1 cup
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Dimensional Analysis
Description
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Explain
Explain that dimensional analysis is an
extremely powerful problem-solving tool.
Learning this method requires extra effort on
the part of students. They must often use
multiple conversion factors. The extra effort
can be justified because the proper
manipulation of the units assures accurate
manipulation of the numbers.
Emphasize that students should use
dimensional analysis as a tool for solving all
of the problems they encounter in chemistry.
Their first question about any quantity
should be, "What are the units of this
quantity?" By comparing the units of
various quantities in a problem, students
can discover whether they need to perform
any unit conversions before proceeding.
Dimensional Analysis
Description
Explain
Explain that measurements are often made
using one unit and then converted into a
related unit before being using in
calculations. For example, students might
measure volume in liters or milliliters in the
laboratory, but express it as cubic
centimeters in a calculation. Explain to the
students that conversions are done using
conversion factors. Emphasize that these
conversion factors are ratios of equivalent
physical quantities, such as 1 mL/1 cm3.
Reassure students that they are more
familiar with conversions than they may
realize. Point out examples of everyday
conversions, such as converting money
from cents to dollars and converting time
from minutes to hours. Start out by giving
them practice with everyday examples.
Ask A chicken needs to be cooked 20
minutes for each pound it weighs. How
long should the chicken be cooked if it
weighs 4.5 pounds? (4.5 lb × 20 min/lb = 90
min; 90 min × 1 h/60 min = 1.5 h. Most
students will automatically relate 90 minutes
to 1.5 hours. This may help them become
comfortable with the process.)
If students are having difficulty with
conversion factors, provide a more tactile
environment for students to discover these
relationships.
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Content
3.3 Chemistry Tutorial:
Using Density as a
Conversion Factor
Content
3.3 Chemistry Tutorial:
Converting Ratios of Units
Have students complete 3.3 Chemistry
Tutorial: Using Density as a Conversion
Factor and 3.3 Chemistry Tutorial:
Converting Ratios of Units on
PearsonChem.com.
Dimensional Analysis
Description
Resources
Pacing
Explore
Have students use dimensional analysis to
convert between English and metric units.
Distribute the media guides (if necessary)
and assign each group of students a set of
players. Ask the group to convert heights
and weights into heights and masses
expressed in meters and kilograms,
respectively. Have students document their
approach, including dimensional analysis
expressions, conversion factors, and
calculations.
Materials: Internet access or copies of
media guides containing vital statistics,
such as heights and weights of players on a
sports team (These guides are available
from local sports franchises.)
Assess and Remediate
Description
Evaluate
To determine students' grasp of conversion
factors, ask students to orally explain the
relationship between the numerator and the
denominator of any measurement
conversion factor. (They are equivalent so
that the ratio of numerator to denominator
equals 1.)
Then, have students complete the 3.3
Lesson Check.
Remediate
Model the conversion of 2 L to 2000 mL.
Suggest that students check the answer by
explaining that when using a conversion
factor, such as 1 L = 1000 mL, the
measurement expressed with the smaller
unit (mL) should have a larger number
associated with it than the measurement
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Resources
Content
Pacing
Chapter 3 Online Student
Edition
expressed with the larger unit (L).
Chapter 3 Review
Description
Resources
Choose from the chapter review and
assessment resources for Chapter 3:
Scientific Measurement listed at the right.
Pacing
Content
Ch. 3 Math Tutorial A:
Converting Units
Content
Ch. 3 Math Tutorial B:
Scientific Notation
Content
Ch. 3 Problem Set
Content
Ch. 3 Core TR: Chapter
Quiz
Content
Ch. 3 Core TR: Chapter
Test A
Content
Ch. 3 Core TR: Chapter
Test B
Differentiated Instruction
Description
Resources
Less Proficient Readers
Students may benefit from a reminder that
certain key words and phrases in each word
problem indicate the unknown quantity and
its units. Some of these phrases are: how
much, what is, how long, determine, and
find.
Struggling Students
When writing problems on the board,
assign a different color to each unique unit
of measurement in the problem. This will
assist students in understanding that a unit
in the numerator can only be cancelled by
an equivalent unit in the denominator.
Advanced Students
Direct students' attention to Tables 3.3, 3.4,
and 3.5. Have students express the ratio in
scientific notation between the largest and
smallest units listed in each table. (Table 3.3:
12
6
1 × 10 ; Table 3.4: 1 × 10 ; Table 3.5: 1 ×
109)
Focus on ELL
page 6 of 7
Pacing
Content
Table 3.3
Content
Table 3.4
Content
Table 3.5
Content
Study WB Chapter 3
Lesson 3
Content
Ch. 3 Core TR: Section 3
Review
Description
Content and Language
Present academic vocabulary for this lesson,
such as analyze, calculate, and evaluate.
Pronounce the words and have students
repeat them. Provide explanations,
examples, and visuals of each word so
students are aware of what tasks lie ahead
when they encounter these words.
My Notes
page 7 of 7
Resources
Pacing
Content
Study WB Chapter 3
Lesson 3
Content
Ch. 3 Core TR: Section 3
Review
Homework