Chemistry
HS/Science
Unit: 08
Lesson: 01
Suggested Duration: 12 days
Stoichiometric Calculations
Lesson Synopsis:
After completing the previous unit on chemical reactions, students are ready to apply the law of conservation of mass to
stoichiometric calculations. Students first explore uncertainty, the importance of measuring with accuracy and precision,
and the need for rules pertaining to significant figures. Then, using Avogadro’s number, balanced equations, and molar
masses, they learn to do mole-mole, mole-mass, and mass-mass calculations, in which they must express chemical
quantities using significant figures and scientific notation. Next, students apply problem solving steps of stoichiometry to
real world problems. Finally, through laboratory investigations, they explore relationships between reactants and products
in order to determine limiting reactants/reagents and percent yield from a reaction.
TEKS:
C.8
C.8E
The student can quantify the changes that occur during chemical reactions. The student is expected to:
Perform stoichiometric calculations, including determination of mass relationships between reactants and products,
calculation of limiting reagents, and percent yield. Supporting Standard
Scientific Process TEKS:
C.1
C.1A
C.1B
C.1C
C.2
C.2E
C.2F
C.2G
C.2H
C.2I
The student, for at least 40% of instructional time, conducts field and laboratory investigations using safe,
environmentally appropriate, and ethical practices. The student is expected to:
Demonstrate safe practices during field and laboratory investigations.
Know specific hazards of chemical substances such as flammability, corrosiveness, and radioactivity as
summarized on the Material Safety Data Sheets (MSDS)
Demonstrate an understanding of the use and conservation of resources and the proper disposal or recycling of
materials.
The student uses scientific methods to solve investigative questions. The student is expected to:
Plan and implement investigative procedures, including asking questions, formulating testable hypotheses, and
selecting equipment and technology, including graphing calculators, computers and probes, sufficient scientific
glassware such as beakers, Erlenmeyer flasks, pipettes, graduated cylinders, volumetric flasks, safety goggles, and
burettes, electronic balances, and an adequate supply of consumable chemicals.
Collect data and make measurements with accuracy and precision.
Express and manipulate chemical quantities using scientific conventions and mathematical procedures, including
dimensional analysis, scientific notation, and significant figures.
Organize, analyze, evaluate, make inferences, and predict trends from data.
Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings,
graphs, journals, summaries, oral reports, and technology-based reports.
GETTING READY FOR INSTRUCTION
Performance Indicator(s):
•
Write a summary of an investigation to find the optimum combination of two reacting substances to obtain the
greatest percent yield of product. Describe the results of each of the trials, and show all calculations including the
amount of product for each trial, the limiting reagent, and percent yield. Discuss how the best combination was
determined. (C.2G, C.2H, C.2I; C.8E)
3E; 5B, 5G
Key Understandings and Guiding Questions:
•
•
The law of conservation of matter governs chemical reactions.
— What is the mathematical relationship between the reactants and the products?
— What is the mathematical process involved in the calculation of the amount of products produced in a
chemical reaction?
The mathematical calculations used in chemical stoichiometry involve the correct use of moles, dimensional
analysis, scientific notation, and significant figures.
— How can measured quantities be manipulated using conversion factors derived from balanced chemical
equations?
— How can very large or very small measured quantities be expressed with accuracy?
©2012, TESCCC
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Chemistry
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Unit: 08 Lesson: 01
—
•
How can dimensional analysis be used to calculate quantities of reactants or products involved in chemical
reactions?
The amount of products in a chemical reaction is determined by the amount of the reactants.
— How can a limiting reactant be determined?
— How are limiting reactants used to calculate the amount of products produced in a chemical reaction?
Vocabulary of Instruction:
•
•
•
stoichiometry
stoichiometric calculations
limiting reactant (reagent)
• percent yield
• accuracy
•
•
precision
uncertainty
Materials:
Refer to Notes for Teacher section for materials.
Attachments:
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Teacher Resource: Dart Game (1 for projection)
Teacher Resource: Measure With Meaning Station Cards (see Advance Preparation, 1 card per station)
Teacher Resource: PowerPoint: The Mathematics of Chemistry: Significant Figures
Handout: Unit 08 Practice Problems (1 per student)
Teacher Resource: Unit 08 Practice Problems KEY
Teacher Resource: PowerPoint: The Mathematics of Chemistry: Stoichiometry/Dimensional Analysis
Handout: Stoichiometric Calculations: The Plan (1 per student)
Handout: Start by Measuring in Moles (1 per student)
Teacher Resource: Start by Measuring in Moles KEY
Handout: The Mathematics of Chemistry Format: Guided Practice (1 per student)
Teacher Resource: The Mathematics of Chemistry Format: Guided Practice KEY
Handout: Chart It! (1 per student and 1 for projection)
Teacher Resource: Chart It! KEY
Teacher Resource: The Chemistry of Latent Fingerprints (1 for projection)
Teacher Resource: The Chemistry of Latent Fingerprints KEY
Handout: The Mathematics of the Combustion Reaction (1 per student for half the class)
Teacher Resource: The Mathematics of the Combustion Reaction KEY
Handout: The Mathematics of the Carbon Dioxide Scrubber (1 per student for half the class)
Teacher Resource: The Mathematics of the Carbon Dioxide Scrubber KEY
Handout: Calculate the Cake (1 per pair of students)
Teacher Resource: Calculate the Cake KEY
Handout: Stoichiometry in the Real World: Limiting Reactants (1 per student)
Teacher Resource: Stoichiometry in the Real World: Limiting Reactants KEY
Handout: Limiting Reactants Practice
Teacher Resource: Limiting Reactants Practice KEY
Handout: Limiting Reactants and Percent Yield (1 per student)
Handout: Reaction to Perfection PI (1 per student)
Teacher Resource: Performance Indicator Instructions KEY
Advance Preparation:
1. Throughout this lesson, it may be helpful to have molecular model sets available to model reactions.
2. Create a griddable template for students to practice using with their calculations.
3. If you have not already had your students affix a copy of the STAAR Chemistry Reference Materials in their
science notebooks, you will need to provide copies of the Reference Materials for their use in the lesson.
4. Prior to Day 1:
• Prior to the Dart Game activity, read the Background Information section, as well as other resources, to
refine your understanding of precision, accuracy, and random measurements.
©2012 TESCCC
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Chemistry
HS/Science
Unit: 08 Lesson: 01
•
•
Print and laminate Measure with Meaning Station Cards. You will need one card for each station.
Cut strips of paper or cardstock to the same length for the Explore: Measure with Meaning Length Stations.
•
5.
6.
7.
8.
Place 22 mL of water in various types of containers, such as graduated cylinders, beakers, and Erlenmeyer
flasks, for the Explore: Measure with Meaning volume stations.
• Set up stations using the Teacher Resource: Measure with Meaning Station Cards and the materials list in
the Notes for Teacher section as a reference. Note: There are three stations for the Explore activity, but it
may be helpful to set up multiple stations to accommodate class size.
• Prepare a large data table for students to contribute class data for observations and discussion.
Prior to Day 6, determine what format will be used for presentation of solutions from the Handouts: The
Mathematics of the Combustion Reaction and The Mathematics of the Carbon Dioxide Scrubber.
Prior to Day 8, consider bringing copies of recipes and cookbooks to use as examples with the Calculate the
Cake activity and also to provide cooking equivalents that could be used to model additional limiting reactant
simulations or stoichiometry practice.
For Days 9–12 (Explore/Explain, Elaborate, and Evaluate):
• Select and organize measuring equipment (balances, glassware) for the investigations. The greater the
variety of measuring equipment you provide, the more choices will be offered to students for planning and
conducting their Elaborate investigations.
• Note: The Explore/Explain investigation is designed to provide less than precise or accurate results by using
7 grams of copper (II) sulfate and 2 grams of iron.
• In the Elaborate that follows, students will plan and implement improvements to get better yield (accuracy)
and better class consistency (precision).
• Equipment examples include:
—
electronic balance, triple beam balance, analytical balance
—
graduated cylinders of different sizes and graduations/uncertainty
• Obtain and put out MSDS sheets for safety. It may be helpful to laminate the sheets for durability.
• Prepare a method for class sharing of data.
Prepare attachment(s) as necessary.
Background Information:
Every measurement in science has a degree of uncertainty associated with it. There are two components to uncertainty:
limitations to accuracy and limitations to precision.
Accuracy refers to how closely a measurement comes to the accepted or true value. A measurement may be very
reproducible but not be very accurate, that is, not measure what it is supposed to measure. Finding the source of
inaccuracy may require measuring with different tools or methods; it may not be easy to specify the source and limitations
of the uncertainty.
Precision refers to reproducibility and relates to the variations found when the same measurement process is used
repeatedly. All measurements have this type of uncertainty related to both the nature of the instrument and the
investigator’s abilities to use the instrument (but not improper use).
Suppose that a student was using a balance that was not zeroed (tared) properly. The mass values from the balance could
be very precise (reproducible) but not accurate. Another balance would be necessary to check on the accuracy of the
original measurements.
There are three ways of expressing uncertainty in precision: +/-, %, and significant figures. Some typical +/- uncertainties
are shown below:
• platform balance +/- 0.5 g
• triple-beam (centigram) balance +/- 0.01 g
• electronic balance +/- 0.002 g
• 10 mL graduated cylinder +/- 0.1 mL
• 50 mL graduated cylinder +/- 0.2 mL
• -10oC to 110oC thermometer +/- 0.2oC
For example, suppose a student massed a piece of aluminum on a triple beam balance as 2.50 +/- 0.01 g. We would
©2012 TESCCC
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Chemistry
HS/Science
Unit: 08 Lesson: 01
expect that if the measurements were repeated many times, 2.50 g, 2.51 g, and 2.49 g would be the most common values.
The same uncertainties could be expressed as a % of the measurement. As a percent, the uncertainty would be:
(0.01g/2.50g) x 100% = +/- 0.4%.
The third way, using significant figures, expresses the number of digits that are certain and first uncertain digit. Obviously,
using significant figures does not give as much information as the previous two methods. However, for the purposes of this
course, indicating uncertainty by using significant figures is satisfactory.
As part of the Chemistry Scientific Process TEKS, students are required to collect data and make measurements with
accuracy and precision and to use significant figures. The Rules for Significant Figures is a section included on the STAAR
Chemistry Reference Materials.
Stoichiometry is the study of the quantitative relationships between reactants and products in chemical reactions. The
term is derived from two Greek root words: stoicheion, meaning "element", and metron, meaning "measure”. The
calculations of moles and masses of reactants and products are referred to as stoichiometric calculations. All
stoichiometric calculations begin with a balanced equation. The coefficients of a balanced equation show the relative
numbers of moles of reactants and products in a chemical process, the mole ratio of one reactant to the other(s), and of
the reactants to the products. These mole ratios are necessary for the calculation of amounts of reactants and products.
Dimensional (also called unit) analysis is the problem-solving strategy used to complete stoichiometric calculations. As
with any chemistry calculation, using units helps to correctly manipulate the quantities that are given and that are to be
found. It guides a student to determine the steps that should be followed in problem solving.
Here are the steps to be used to solve stoichiometry calculations using dimensional analysis. See the examples below.
1. Write the chemical equation.
2. Balance the chemical equation.
3. *Follow steps to dimensional analysis:
• Start with what is given.
• Set up a series of equivalent measures.
• End with your goal.
• Solve the problem by cancelling units.
• Record the appropriate answer with units.
Sample Mass-Mass Problem:
In a chemical reaction to produce copper (I) sulfide, how many grams of sulfur are required to react completely with 80.0
g of copper?
1. Write the chemical equation with reactants and products.
Cu + S ---- Cu2S
2. Balance the chemical equation.
2Cu + S ---- Cu2S
3. Start with what is given: g Cu = 80.0 g
Set up series of equivalent measures.
End with your goal: g S= ?
80.0 g Cu X 1 mol Cu X 1 mol S
63.5 g Cu
2 mol Cu
X 32.1g S
1 mol S
=?
gS
Solve the problem by cancelling units.
Record the appropriate answer with units and the correct number of significant digits.
80.0 g Cu X 1 mol Cu X 1 mol S
63.5 g Cu
2 mol Cu
©2012 TESCCC
X 32.1g S
1 mol S
= 20.2 g S
05/08/13
page 4 of 16
Chemistry
HS/Science
Unit: 08 Lesson: 01
The sample above is called a mass-mass problem. Other types of stoichiometric calculations are mole-mole, mass-mole,
and mole-mass problems.
In some chemical reactions, the proportion of reactants/reagents involved may not match the ratio indicated by the
balanced equation. In this situation, one or more reactants will be in excess and one will be used up. The reactant that is
used up is the limiting reactant and determines the quantity of product(s) that will be produced. Stoichiometric
calculations are used to determine the limiting reagent/reactant.
Example:
90.0 g of FeCl3 reacts with 52.0 g of H2S.
2FeCl3 + 3H2S  6HCl + Fe2S3
1. What is the limiting reactant? FeCl3
2. What is the actual mass of HCl produced? 60.8 g HCl
3. What mass of excess reactant remains after the reaction? 23.6 g H2S
90.0 g FeCl3 X 1 mol FeCl3 X 6 mol HCl
X 36.5 g HCl
162 g FeCl3
2 mol FeCl3
1 mol HCl
= 60.8 g HCl
52.0 g FeCl3 X 1 mol H2S X 6 mol HCl
34.1 g H2S
3 mol H2S
= 111 g HCl
X 36.5 g HCl
1 mol HCl
Limiting Reactant = FeCl3
90.0 g FeCl3 X 1 mol FeCl3 = 6 mol H2S
X 34.1 g H2S
162 g FeCl3
2 mol FeCl3
1 mol H2S
= 28.4 g H2S reacted
52.0 g H2S – 27.4 g H2S = 23.6 g H2S excess
Stoichiometric calculations give the expected or theoretical yield of products in a chemical reaction.
In the laboratory and in industry, chemical reactions do not always occur with 100% efficiency and the product(s) that
result may be less than predicted by the balanced equation. The percent yield is determined by comparing the actual
yield to the theoretical yield. As found in the STAAR Chemistry Reference Materials,
% yield = (actual yield / theoretical yield) x 100 %
Example:
In the above reaction, if the experiment was done in the lab and 55.9 g of HCl was produced, determine the percent yield.
% yield = 55.9 g HCl (actual) / 60.8 g HCl (theoretical) x 100% = 91.9%
GETTING READY FOR INSTRUCTION SUPPLEMENTAL PLANNING DOCUMENT
Instructors are encouraged to supplement and substitute resources, materials, and activities to differentiate instruction to address the needs of learners.
The Exemplar Lessons are one approach to teaching and reaching the Performance Indicators and Specificity in the Instructional Focus
Document for this unit. Instructors are encouraged to create original lessons using the Content Creator in the Tools Tab located at the top of the page.
All originally authored lessons can be saved in the “My CSCOPE” Tab within the “My Content” area.
INSTRUCTIONAL PROCEDURES
Instructional Procedures
Notes for Teacher
ENGAGE – The Dart Game
NOTE: 1 Day = 50 minutes
Suggested Day 1
©2012 TESCCC
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Chemistry
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
1. Project the Teacher Resource: Dart Board, a blank target
template. Ask students to draw it in their science notebook four
times.
Attachment:
•
Teacher Resource: Dart Game (1 for
projection)
2. Instruct students to label their targets as follows:
• random
• high precision and low accuracy
• high accuracy and low precision
• high precision and high accuracy
Instructional Note:
A model of a dartboard is an interactive way to
introduce students to differences among
accurate, precise, and random measurement
results. Suggested time is 10–15 minutes.
3. Pose the following question:
• What would dart holes patterns look like for each of
these patterns?
4. Instruct students to individually draw six small circles on each of
their targets to represent dart holes patterns.
Science Notebooks:
Students record observations and write tentative
definitions and illustrations of each of the four
target scenarios in their notebooks.
5. Allow a couple of minutes, and then instruct students to compare
and discuss their targets with a partner.
6. Project the four targets in the resource one at a time: random,
high precision and low accuracy, high accuracy and low
precision, and high precision and high accuracy.
7. For each target, ask students to compare their drawings with the
resource. Instruct students to correct or revise their targets as
needed.
8. In their notebooks, ask students to write definitions of accurate,
precise, and random, based on the examples just provided.
9. Ask several volunteers to share their definitions. Accept all
reasonable answers. Inform students you will return to these
definitions later in the lesson.
EXPLORE/EXPLAIN – Measuring with Meaning
Suggested Day 1 (continued)
1. Hold up a meter stick and strip of paper (see Advance
Preparation).
Pose the following question:
• If I try to measure this strip of paper with a meter stick
several times, will I get the same length measurement
each time? Why or why not? Accept all reasonable
answers.
2. Hold up a metric ruler and the same strip of paper. Continue the
discussion:
• If I try to measure this strip of paper with a metric ruler
several times, will I get the same length measurement
each time? Why or why not? Accept all reasonable
answers.
• How is measuring the strip with the metric ruler
different from measuring with the meter stick? Accept all
reasonable answers.
©2012 TESCCC
05/08/13
Materials:
•
meter stick (for demonstration, 1 per
teacher)
•
metric ruler (for demonstration, 1 per
teacher)
•
beaker with graduations (250 mL,
containing water, for demonstration, 1 per
teacher)
•
graduated cylinder (100 mL, for
demonstration, 1 per teacher)
•
pipette (for demonstration, 1 per teacher)
•
water (for demonstration)
•
metric rulers (variety of wooden, plastic,
metal, several per Length Station)
•
meter sticks (1 per Length Station)
page 6 of 16
Chemistry
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
3. Hold up a 250 mL beaker containing water.
• If I try to measure the volume of the liquid in the beaker
several times, will I get the same volume measurement
each time? Why or why not? Accept all reasonable
answers.
• What if I measure the volume of the liquid in the beaker
using this graduated cylinder? How will the
measurement be affected? Accept all reasonable answers.
4. Inform students you want to give them more experience with
measurement and uncertainty.
5. Divide the class into groups of 2–4. Instruct groups to rotate
through three stations (Length, Mass, and Volume), recording
measurements and observations in their science notebooks.
You may wish to give students a signal for rotation to the next
station.
6. Monitor students as they complete the station activities.
7. When students have finished measuring, instruct student groups
to average and then compare their measurements with their
other group members.
8. Ask representatives from groups to enter data into a cumulative
class data table for display for the class and discussion (see
Advance Preparation).
9. Ask students to respond to the following instructions and record
answers/notes in their science notebooks:
• Discuss with a partner what you experienced that
exemplified precision and accuracy.
• Summarize, in writing, what you observe about the class
data.
• Make adjustments to definitions and applications, as
necessary, from your experiences.
• Explain the differences in accuracy and precision. Record
an example of each.
10. Use a cooperative grouping or partner strategy, instruct students
to share their responses.
11. Using an exit ticket strategy (see Check for Understanding), ask
students to record their answer to the following:
• What makes a measurement more precise?
• Give an example.
•
•
•
•
•
•
•
strips of paper (of uniform length, see
Advance Preparation, several per Length
Station)
balances (variety such as electronic, triple
beam, analytical, if available, per Mass
Station)
objects (must be equal mass, such as 1 oz.
weights, 1 per Mass Station)
beakers (250 mL or Erlenmeyer flask, 2–3
per Volume Station, 1 containing 22 mL of
water)
graduated cylinder (100 mL, 2–3 per
Volume Station, 1 containing 22 mL of
water)
graduated cylinder (25 mL, 2–3 per Volume
Station, 1 containing 22 mL of water)
pipettes (several per Volume Station)
Attachment:
• Teacher Resource: Measure With
Meaning Station Cards (see Advance
Preparation, 1 card per station)
Instructional Notes:
Student groups will rotate through three different
stations for measurements. You may want to set
up three or more of each station to minimize
group size and waiting times.
Ensure strips of paper are the same length for a
meaningful discussion of accuracy and
precision.
Varieties of rulers, such as wooden, plastic,
metal, and meter sticks are necessary.
Check for Understanding:
An exit ticket strategy is a way to check for
student understanding. Students respond to
your question and turn it in to you prior to the
bell.
This provides an opportunity to review student
ideas and thinking to help direct the lesson that
follows.
Science Notebooks:
Students record data and make calculations in
their science notebooks.
©2012 TESCCC
05/08/13
page 7 of 16
Chemistry
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
EXPLAIN – Significant Figures
Suggested Day 2
1. Discuss students’ measurement results using various tools, and
relate this process to uncertainty, accuracy, and precision.
Revisit the example of throwing darts at a target, as necessary.
2. Discuss uncertainty and error, and introduce the use of
significant figures as a way to communicate the precision of
measurements. Distinguish between mistakes and error in
measurements.
3. Refer students to their STAAR Chemistry Reference Materials,
or distribute a copy to each student as needed (see Advance
Preparation). Instruct students to locate the Rules for Significant
Figures.
4. Project the Teacher Resource: PowerPoint: The Mathematics
of Chemistry: Significant Figures. Do this interactively,
pausing to discuss each slide and ask guiding questions of
students. Note: Information for the slides is located in the slide
notes of the presentation.
5. Instruct students to take notes in their science notebooks as the
information is discussed. Use a partner sharing strategy as
appropriate:
• For the appropriate slides, ask students to independently
and silently determine significant figures and to cite the
rule(s) from the STAAR reference chart.
• Then, instruct students to turn to a partner and discuss the
answer.
• Next, call on a group to share their consensus and the
supporting rule.
• Guide the discussion, and use questioning to keep students
engaged.
• Check for understanding and misconceptions frequently.
6. Inform students that the course requirement from now on will be
that students will always do calculations and report answers with
the correct number of significant figures.
Materials:
• glue or tape (per group)
Attachments:
• Teacher Resource: PowerPoint The
Mathematics of Chemistry: Significant
Figures
• Handout: Unit 08 Practice Problems (1 per
student)
• Teacher Resource: Unit 08 Practice
Problems KEY
Instructional Notes:
For additional information conduct an Internet
search for measurement and uncertainty in
science.
This activity provides practice with different
skills and will be revisited throughout the unit.
STAAR Note:
The STAAR Chemistry Reference Materials
include Rules for Significant Figures.
Science Notebooks:
Students take notes and affix practice problems
in their notebooks.
7. Present the Scientific Notation slide. Verify the significant figures
in the four examples.
Discuss the following:
• How can very large or very small measured quantities
be expressed with accuracy? Use scientific notation for
very large and very small numbers; the last digit in the
number is the uncertain digit.
8. Distribute the Handout: Unit 08 Practice Problems to each
student. Assign Sections A, B, and C on significant figures,
scientific notation, and calculations. Note: Students will complete
Section D later in the unit.
9. Circulate and provide assistance as needed. Instruct students to
verify their answers with a partner. Address any misconceptions.
©2012 TESCCC
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Chemistry
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
10. Instruct students to affix the handout in their science notebooks
for reference, but leaving additional room for problem solving of
Section D.
EXPLORE/EXPLAIN – Stoichiometry: Solving Problems
Suggested Day 3
1. Briefly review problems and concepts from the previous day’s
activity with students.
2. Write or project the terms Stoichiometry and Dimensional
Analysis on the board, and ask students to discuss the meaning
of these terms with partner.
3. Ask for comments, and then discuss as needed.
4. Present the Teacher Resource: PowerPoint: The Mathematics
of Chemistry: Stoichiometry/Dimensional Analysis . As you
show each slide, involve students with the guided practice.
5. Instruct students to take notes on the steps in their science
notebooks.
6. Distribute the Handout: Stoichiometric Calculations: The Plan
to each student. The purpose of the handout is to firmly
establish the dimensional analysis process. Instruct students to
affix the handout to their science notebooks.
7. Allow students a few moments to read the handout. Review the
steps again with students.
8. Facilitate a discussion in which students reflect on the following:
• How can dimensional analysis be used to calculate
quantities of reactants or products involved in chemical
reactions? Accept appropriate answers.
• Begin with what is to be found and what is given; stepby-step conversions are set-up as outlined in
Stoichiometric Calculations: The Plan.
• Each component must have the correct units.
• A check of the process is to determine that all units
cancel except units belonging to the quantity being
determined.
9. Distribute the Handout: Start by Measuring in Moles to each
student.
10. Remind students of the mole concept from Unit 06 and the
process of balancing equations from Unit 07.
11. You may wish to have molecular models available to support the
concept of conservation of mass.
12. When students have completed the handout:
Pose the following question:
• What is the mathematical relationship between the
reactants and the products? (Matter is conserved. There
are the same number and kinds of atoms in the products as
©2012 TESCCC
05/08/13
Materials:
• glue or tape (per group)
• molecular models (see Advance
Preparation, 1 set per teacher or group) –
Optional
Attachments:
• Teacher Resource: PowerPoint: The
Mathematics of Chemistry:
Stoichiometry/Dimensional Analysis
• Handout: Stoichiometric Calculations:
The Plan (1 per student)
• Handout: Start by Measuring Moles (1 per
student)
• Teacher Resource: Start by Measuring
Moles KEY
• Handout: The Mathematics of Chemistry
Format Guided Practice (1 per student)
• Teacher Resource: The Mathematics of
Chemistry Format Guided Practice KEY
Instructional Notes:
Use dimensional analysis to show students how
this technique will aid them in correctly solving
stoichiometric calculations.
The last slide of the PowerPoint provides an
optional opportunity for students to develop their
own basic stoichiometry calculations. This may
be early for some students, but while it may
prove to be challenging, it may help for students
to identify components of the problem. This may
be a good strategy to use throughout the unit.
Key Points:
• A balanced equation represents the
smallest whole number ratio of reactants
and products.
• A balanced equation represents atoms,
molecules, formula units, or moles.
• A balanced equation is always the starting
point in stoichiometry to determine the
amount of reactant and products in a
chemical reaction.
• Balanced equations can be applied to
chemical processes in the laboratory and in
the real world.
page 9 of 16
Chemistry
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
in the reactants.)
13. Instruct students to complete the handout independently.
14. Monitor and assist as necessary.
15. Distribute the Handout: The Mathematics of Chemistry
Format Guided Practice to each student.
16. Model using dimensional analysis to solve each problem as
students take notes.
17. Discuss the following:
• What is the mathematical process involved in the
calculation of the amount of a product in a chemical
reaction? (Use dimensional analysis, starting with the
givens and the mole ratio, from the balanced equation.)
18. Monitor and assist as necessary.
This activity uses dimensional analysis to solve
mole-mole, mole-mass, and mass-mass
calculations where more than one reactant or
product is part of the calculation.
These calculations involve the use of
equivalents to solve the problem. Students need
to have a deep understanding of the concept of
equivalents and relate those to the units of
measurement common in stoichiometry- moles,
molar mass, and Avogadro’s number.
Prior to stoichiometry calculations, you may
choose to have students practice dimensional
analysis with common units to practice setting
up equivalents and solving the calculation while
using the correct number of significant digits.
Examples could be converting:
• centimeters to feet
• tablespoons to gallons
• years to hours
Science Notebooks:
Students work mole-mole problems in their
science notebooks.
EXPLORE/EXPLAIN – Chart It!
Suggested Days 4 and 5
1. Provide each student with the Handout: Chart It!.
2. Instruct students to work independently to complete the Chart It!
#1 using the Periodic Table and their notes for assistance.
3. Monitor and assist as needed.
4. After they have completed Chart It #1, pair the students and
instruct them discuss and come to agreement on their results.
5. Call on a several students to share calculations with the class.
Clarify misconceptions as necessary:
• What data on the chart is consistent with the law of
conservation of matter (mass)? The mass of the products
calculated does equal the mass of the reactants.
6. Working in pairs, instruct students to complete the other three
reactiontocharts.
14. Chart
InstructIt!students
complete Section D: Stoichiometry,
15. Monitor students as they work; answer questions, and assist as
needed.
16. A time allows, instruct students to work problems for the class to
model their thinking.
©2012 TESCCC
05/08/13
Materials:
• glue or tape (per group)
Attachments:
• Handout: Chart It! (1 per student and 1 for
projection)
• Teacher Resource: Chart it! KEY
• Handout: Unit 08 Practice Problems (from
previous activity)
• Teacher Resource: Unit 8 Practice
Problems KEY
Instructional Notes:
Remind students that significant figures should
be used in stoichiometric calculations.
Additionally, they may need to be reminded of
the diatomic elements and their significance in
calculations.
Point out to students that these calculations
provide what are known as “theoretical”, or
page 10 of 16
Chemistry
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Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
“expected” values, of products. When a reaction
is completed and the mass(es) of product(s) are
measured, these values are known as “actual.”
This understanding helps provide background
for percent yield: actual/theoretical.
STAAR NOTE:
Percent yield is a formula listed on the STAAR
Chemistry Reference Materials.
Science Notebooks:
Students take notes, affix handouts and work
problems in their notebooks.
Suggested Days 6 and 7
ELABORATE – Stoichiometry Applications
1. Project Teacher Resource: The Chemistry of Latent
Fingerprints (see Instructional Notes) to use as a focus to
review prior learning.
2. Instruct students to read and work independently for a short
period or use the resource as a focus question to connect to
prior learning. Students should record their work in their science
notebooks.
3. Divide the class into partners to discuss their steps to derive the
solution.
4. Select a team to share their solution process with the class.
Instruct other students to contribute as required. Ensure
dimensional analysis was done properly.
5. Provide half of the pair groups the Handout: The Mathematics
of the Combustion Reaction and other half the Handout: The
Mathematics of Carbon Dioxide Scrubbers.
6. Instruct students to read their handouts and solve the problem
showing the steps they use. Check for appropriate use of
dimensional analysis, scientific notation, and significant figures
appropriately.
7. Students should prepare an organized poster (or visual aid) to
present their solutions to the class. NOTE: If your technology
and user agreements allow, students could make a video of their
explanation and post it to an approved video podcast source.
8. Ask a selection of groups to present their solutions to the class.
Answer any questions that students have about calculations,
and encourage connections among the calculations.
9. If time is short, consider posting the solutions and conducting a
gallery walk with time for sharing.
©2012 TESCCC
05/08/13
Materials:
• poster paper (1 per group)
• markers (per group)
Attachments:
• Teacher Resource: The Chemistry of
Latent Fingerprints (1 for projection)
• Teacher Resource: The Chemistry of
Latent Fingerprints KEY
• Handout: The Mathematics of the
Combustion Reaction (1 per student for
half the class)
• Teacher Resource: The Mathematics of
the Combustion Reaction KEY
• Handout: The Mathematics of the Carbon
Dioxide Scrubber (1 per student for half the
class)
• Teacher Resource: The Mathematics of
the Carbon Dioxide Scrubber KEY
Instructional Notes:
Consider printing student copies of the Teacher
Resource: The Chemistry of Latent
Fingerprints for all students or for vision
impaired students.
For practice, you may choose to instruct
students to record answers to these problems in
a griddable document following the TEA STAAR
guidelines. Copies could be made for
independent practice or led by students through
interaction with an electronic white board.
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Chemistry
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Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
By dividing the practice, all students get
applicable practice and yet will experience each
scenario as groups share out solutions to class.
If you feel your students need additional
practice, you could use one of the activities for
practice outside of class.
Science Notebooks:
Students work practice problems in their
science notebooks.
EXPLORE – Calculate the Cake
1. Pose the following:
• How is a recipe analogous to a chemical equation? (A
recipe shows the amount of each ingredient needed to
make the cake, and an equation shows the “chemical
recipe” for a reaction and gives information about the
amount of product(s) that can be made from the reactants
that are present.) Accept all reasonable answers.
2. Organize students into pairs. Provide each pair of students with
the Handout: Calculate the Cake.
3. Inform students they are going to investigate the similarity of a
recipe to a chemical equation.
4. Instruct students to read and complete the activity and record
their calculations in their science notebooks. Answer any
questions students may have about the handout.
5. After students have completed the activity, ask:
• How many cakes can your group make? (2)
• If you have 50 cups of flour and each cake takes 2 cups,
why can your group not make 25 cakes? The other
ingredients run out.
• Which ingredient limits the number of cakes your group
can make to 2? Why? (Butter. It is present in the least
amount compared to the other ingredients.)
• How is the cake recipe similar to a chemical reaction?
Just as with the cake, the amount of reactant(s) limits the
amount of product(s).
6. Now that the concept of limited reactant/reagent has been
introduced, distribute the Handout: Stoichiometry in the Real
World: Limiting Reactants to each student.
7. Instruct students to complete the handout. Instruct students to
compare results with a partner and discuss discrepancies, as
needed.
8. For additional practice, instruct students to complete problems
D5 and D6 on the Handout: Unit 08 Practice Problems located
©2012 TESCCC
05/08/13
Suggested Day 8
Attachments:
• Handout Calculate the Cake (1 per pair of
students)
• Teacher Resource: Calculate the Cake
KEY
• Handout: Stoichiometry in the Real
World: Limiting Reactants
• Teacher Resource: Stoichiometry in the
Real World: Limiting Reactants Key
• Handout: Unit 08 Practice Problems (from
previous activity)
• Teacher Resource: Unit 08 Practice
Problems KEY
• Handout: Limiting Reactants Practice
• Teacher Resource: Limiting Reactants
Practice KEY
Instructional Notes:
You may want to begin using the word reagent
interchangeably with reactant as the lesson
goes on in order that students become familiar
with both terms.
Consider instructing students to illustrate
vocabulary terms: limiting and excess reactants.
Misconception:
• Students may think chemical reactions use
up all the reactants.
Science Notebooks:
Students work limiting reactant and percent
yield problems in their science notebooks.
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Chemistry
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Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
in students’ science notebooks.
9. Distribute the Handout: Limiting Reactants Practice to each
student. Answer any questions students may have regarding the
handout.
10. Monitor and assist as students complete the handout.
Wrap up the class with discussing the following:
• How can a limiting reactant be determined? By
comparing actual moles of each reactant using the mole
ratios in the balanced equation
• How are limiting reactants used to calculate the amount
of products in a chemical reaction? Moles of the limiting
reactant produce moles of product based on the mole ratios
in the balanced equation.
EXPLORE/EXPLAIN – Limiting Reactants and Percent Yield
1. Review the Unit 08 Practice Problems from Day 8. Solicit
answers and explanations. Instruct students to assess their own
work to make corrections and connections.
2. Divide the class into groups of 2–4. Inform students that they are
going to investigate a chemical reaction in which one of the
reactants is limited, similar to the cake example.
3. Distribute copies of the Handout: Limiting Reactants and
Percent Yield to each student. Allow a few minutes for students
to read the handout. (See the Instructional Notes.)
4. As part of your pre-lab, instruct students to write a reflection on
what they have learned about limiting reactants and percent
yield in their notebooks.
5. Encourage students to identify areas when precision and
accuracy will be significant to the procedures, referring back to
earlier notes to guide their thinking.
6. Instruct students to discuss with their group their notebook
reflections.
7. Instruct students to re-read the investigation and prepare their
science notebooks for recording information and observations.
Answer any questions they may have regarding the instructions.
8. As needed, demonstrate the filtering set-up and procedure or
have assorted equipment available; ask students to select and
set up the equipment needed for filtration.
9. Discuss and demonstrate safety precautions and proper
disposal.
10. Monitor students, posing and answering questions, as they
complete the laboratory investigation.
11. After students have completed the investigation, tabulate the
class results for the class to see.
©2012 TESCCC
05/08/13
Suggested Days 9 and 10
Materials:
• balance (as appropriate for 7 grams, 1 per
group)
• hot plate (1 per group)
• beaker tongs (1 per group)
• beakers (250 mL, 1 per group)
• stirring rods (1 per group)
• distilled water (per group)
• copper (II) sulfate (anhydrous, per group)
• filter paper (per group)
• funnel (1 per group)
• funnel support (1 per group)
• iron filings (per group)
• heat resistant gloves or hot pads (per
group)
• safety goggles (1 pair per student per
group)
Attachments:
• Handout: Limiting Reactants and Percent
Yield (1 per student)
• Handout: Unit 08 Practice Problems (from
previous activity)
• Teacher Resource: Unit 08 Practice
Problems KEY
Safety Notes:
Ensure MSDS for copper sulfate and iron
sulfate are available.
Safety goggles should be worn in this
investigation.
Care should be taken in handling the hot plate
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Chemistry
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Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
and hot chemicals.
Students should be given instructions for the
proper disposal of chemicals.
Instructional Notes:
This investigation is designed to provide less
than precise or accurate results by using 7
grams of copper (II) sulfate and 2 grams of iron.
12. Facilitate a discussion in which students reflect on their
calculations, significant figures, and how both the limiting
reactant and percent yield were determined
13. Instruct students to locate their Handout: Unit 08 Practice
Problems in their notebooks.
14. Instruct students to complete Section D: Stoichiometry, problems
5–6.
15. Monitor students as they work; answering questions and
assisting as needed.
In the Elaborate that follows, students will plan
and implement improvements to get better yield
(accuracy) and better class consistency
(precision).
If funnel supports are not available, a ring stand
and small ring or clay triangle may be used.
16. A time allows, instruct students to do calculations for the class in
order to model their thinking orally.
Science Notebooks:
Students write reflections and plan data tables
related to the Investigation.
ELABORATE – Reaction to Perfection
Suggested Days 11 and 12
1. Facilitate a class discussion using the following questions.:
• Was your data from the last investigation within an
3. Continue the discussion:
• What factors may have affected to your percent yield?
Encourage a variety of answers. Some possible answers
may include the following:
• Balance sensitivity (precision)
• Accuracy and precision with measurements
• The directions (did not call for precise measurements)
• Massing paper not completely dry
• Filtering problems - tear in filter paper or leaky filtration
set-up
• Mistake with stoichiometry calculations
• Significant figures error
4. Distribute to each student a copy of the Handout: Reaction to
Perfection PI. Allow a few minutes for students to read the
handout.
5. Explain to students that they will use what they learned from the
previous investigation in a new investigation in which they will be
responsible for the following:
• Planning and implementing procedures to find the
optimum combination of iron and copper (II) sulfate to
get the maximum yield of iron sulfate
• Selecting and using materials and equipment to get
more precise and accurate results
• Working safely
• Organizing, analyzing, evaluating, and making
©2012 TESCCC
05/08/13
Materials:
• balance (sensitive to 0.01 or 0.001 g, 1 per
group)
• hot plate (1 per group)
• beaker tongs (1 per group)
• beakers (250 mL, varies per group)
• stirring rods (per group)
• distilled water (per group)
• copper (II) sulfate (anhydrous, per group)
• filter paper (per group)
• funnel (1 per group)
• funnel support (1 per group)
• iron filings (per group)
• heat resistant gloves or hot pads (per
group)
• safety goggles (1 pair per student)
• oven (drying, per class)
• pipettes (several per group)
Attachment:
• Handout: Reaction to Perfection PI (1 per
student)
Safety Notes:
page 14 of 16
Chemistry
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
Students will design and plan their own
investigation so safety practices and their plans
must be reviewed prior to allowing students to
do their procedures.
Obtain MSDS for copper sulfate and iron sulfate
and have them available.
Safety goggles should be worn in this
investigation.
Care should be taken in handling the hot plate
and hot chemicals.
Students should be given instructions for the
proper disposal of chemicals.
•
•
•
inferences from data
Graphing the yield of iron sulfate as a function of 1 mole
of iron and as a function of 2 moles of copper sulfate
Communicating valid conclusions supported by the
data
Summarizing valid conclusions
6. Answer any questions students may have regarding the
investigation. Divide the class into groups.
7. Encourage students to spend time reflecting on Unit 08
notebooking activities to guide thinking prior to this activity.
8. Direct students to record pre-lab calculations and predictions for
trials and procedures in their science notebooks. From these,
students can predict outcomes and plan for the investigation
safely to yield optimum results.
9. Provide a method for groups to share their results.
10. Inform students that prior to beginning work in the lab, each
group MUST get approval from you for their procedures with
respect to safety practices and chemical disposal.
11. Monitor group planning, asking and answering questions as
needed.
EVALUATE – Performance Indicator - Reaction to Perfection
Performance Indicator
• Write a summary of an investigation to find the optimum
combination of two reacting substances to obtain the
greatest percent yield of product. Describe the results of
each of the trials, and show all calculations including the
amount of product for each trial, the limiting reagent, and
percent yield. Discuss how the best combination was
determined. (C.2G, C.2H, C.2I; C.8E)
3E; 5B, 5G
1. Refer to the Teacher Resource: Performance Indicator
Instructions KEY and Handout: Reaction to Perfection PI for
©2012 TESCCC
05/08/13
Safety goggles are needed for this activity.
Prior teacher approval of safety is necessary for
this student-designed investigation to ensure all
safety measures are considered.
Instructional Notes:
In this Elaborate activity, students will study
limiting reactants by designing and
implementing a plan to increase the yield of iron
(II) sulfate product.
This Elaborate serves as a culminating
opportunity for students to apply their learning
from this unit and to extend their thinking to a
real world application.
Equipment outlined by students in their plans
may vary by group.
Science Notebooks:
Students record pre-lab calculations and
predictions for trials and procedures in their
science notebooks.
Suggested Day 12 (continued)
Attachments:
• Handout: Reaction to Perfection PI (from
previous activity)
• Teacher Resource: Performance Indicator
Instructions KEY
page 15 of 16
Chemistry
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
information on administering the assessment.
©2012 TESCCC
05/08/13
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