Balancing Chemical Equations – Grade Nine
Ohio Standards
Connection:
Physical Sciences
Benchmark B
Explain how atoms react
with each other to form
other substances and how
molecules react with each
other or other atoms to
form even different
substances.
Indicator 6
Explain that the electric
force between the nucleus
and the electrons hold an
atom together. Relate that
on a larger scale, electric
forces hold solid and liquid
materials together (e.g.,
salt crystals and water).
Indicator 7
Show how atoms may be
bonded together by losing,
gaining, or sharing
electrons and that in a
chemical reaction, the
number, type of atoms and
total mass must be the
same before and after the
reaction (e.g., writing
correct chemical formulas
and writing balanced
chemical equations).
Lesson Summary:
In this lesson, students will learn to explain how atoms and
molecules form different substances during chemical
reactions and how these processes require losing, gaining
or sharing electrons. Students will correctly write chemical
formulas and show how a balanced chemical equation must
have the same number and types of atoms on each side of
the arrow. The students will use ion cards to write formulas
and a hanger balance to show that the mass before and
after a reaction must be the same. Evidence of learning will
be evaluated using a performance assessment in which
students will apply knowledge learned with the models to an
actual chemical reaction.
Estimated Duration: Five hours
Commentary:
This lesson is designed to give students hands-on
experiences with writing formulas for compounds and
balancing chemical equations. This approach allows
students to visualize abstract concepts by using models to
represent ions and compounds. After manipulating the
models, students will have a better understanding of how
chemical equations are balanced and how the Law of
Conservation of Mass applies.
Pre-Assessment:
 Have each student write the answers to the following
questions:
1. What is the difference between an atom and an ion?
An atom is neutral because it has an equal number of
protons and electrons, whereas an ion has a charge
because the atom has lost or gained electrons.
2. What is the charge on a calcium ion if the calcium
atom has lost two electrons?
Positive two (2+).
3. What is the formula of the compound that is produced
when calcium combines with chorine?
CaCl2
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Balancing Chemical Equations – Grade Nine


4. Define the Law of Conservation of Mass.
Atoms are neither created nor destroyed during a chemical reaction. The total mass
of all products is the same as the total mass of all reactants.
5. What does it mean to balance a chemical equation?
A balanced chemical equation has the same number and types of atoms on each side
of the arrow.
Have students discuss their answers in small groups.
Lead a whole-class discussion about the answers to the questions.
Scoring Guidelines:
Use the pre-assessment to evaluate students’ understanding of formula writing, balancing
equations, the concept that atoms gain or lose electrons to form ions and the principle that
mass is conserved during chemical reactions. Also, monitor students as they work together
in their learning groups, informally assessing their individual responses on the quiz and their
understanding of the concepts. Use the results of the formal and informal pre-assessments to
determine how much formal instruction to use in this lesson.
Post-Assessment:
 Give students a sealed, closed container holding a small amount of solution A and a test
tube partially filled with solution B.
 Have students complete the following steps:
1. Measure the mass of the container and its contents.
2. Tilt the sealed container, carefully mixing the contents of the two solutions.
3. Record observations before, during and after the mixing process.
4. Mass the closed container after the mixing process is complete.
 Have students respond to the following questions:
1. Write an explanation accounting for the mass difference/no mass difference before
and after the substances were allowed to combine.
There should be no mass difference in the closed system. Mass is neither created nor
destroyed in a chemical reaction and all of the products of the chemical reaction are
still present in the jar.
2. Classify the observed change as chemical or physical. Support your choice of
classification with evidence from your observations.
The change is chemical. Color change and the formation of a precipitate are
evidences of chemical change.
3. If solution A is strontium nitrate and solution B is sodium bromide, write the correct
formulas for the reactants.
Sr(NO3)2, NaBr
4. Correctly balance the following chemical equation:
AgNO3 + CaBr2  AgBr + Ca (NO3)2
Answer:
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Balancing Chemical Equations – Grade Nine
2AgNO3 + CaBr2  2AgBr + Ca (NO3)2
5. How does the process of massing the container both before and after the reaction
compare to counting atoms (same number and type of atom on both sides of the
equation)?
Each case confirms the law of conservation of mass: matter is neither created nor
destroyed in a chemical reaction.
 Select two solutions that will produce a precipitate or unexpected color change
(laboratory observations consistent with an interpretation for a chemical change).
Concentrations of 0.1 M work well.
 Suggestions for Solution A and Solution B:
1.
Silver nitrate and sodium chloride (produces AgCl, a white precipitate)
2.
Silver nitrate and sodium bromide (produces AgBr, a yellow precipitate)
3.
Calcium nitrate and sodium sulfate (produces CaSO4, a white precipitate)
Option 1:
Use a small clear jar (e.g., baby food jar) that can be closed securely and a small test tube or
any other clear container (e.g., litmus paper vial) that will fit inside the jar. Leave some
space between the top of the test tube and the outside of the container so that the contents can
be mixed. Put enough of solution A into the jar to cover the bottom. Use a pipet to add
solution B to the vial or small test tube and carefully place it inside the container so that no
mixing occurs. Close the lid on the jar. Add clear plastic wrap to contain the chemicals if the
jar leaks. Caution the students to tilt the jar just enough to mix the contents.
Option 2:
Use two sizes of sealable plastic bags in the place of the jar and vial.
Note cautions for any chemicals used and ensure that students use the appropriate personalsafety equipment.
Scoring Guidelines:
See Attachment A, Post-Assessment Rubric.
Instructional Procedures:
Part I: Exploring Electric Forces
1. Use pith balls to demonstrate the attraction between oppositely charged objects and the
repulsion between similarly charged objects. Hang a pith ball by a silk thread. Rub a
rubber rod with fur and touch the pith ball. Show the pith ball is now repelled by the rod
(because each object has the same charge) and attracted to a glass rod that has been
rubbed with silk (because each object has opposite charges).
2. Relate to students that the force of attraction is directly proportional to the magnitude of
each charge and inversely proportional to the square of the distance between the two
charges (Coulomb’s law).
3. Help students make the connection between this demonstration and the attraction
between two ions when ionic compounds form. (Positive and negative ions attract each
other because their charges are opposite. This force of attraction is the ionic bond.)
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Balancing Chemical Equations – Grade Nine
Part II: Writing Formulas
4. Construct cards of two colors, one for positive ions (e.g., Ca +2, Na +1, Al +3, NH4 +1) and
the other for negative ions (e.g., F –1, O –2, SO4 –2). Make the cards with card stock.
Label one side with the element symbol and the other side with the ion symbol.
Instructional Tip:
Have students construct their own cards as a good learning activity.
5. Have students work in small groups to select two cards, one of each color, to represent a
compound. Have them complete the chart for the compound, writing the formula for the
compound formed between the two ions and indicating the number of electrons that were
lost or gained when the ion formed. See Attachment C, Formula Writing for a student
version of the chart. Have students continue the process for additional compounds.
Positive Ion
(Cation)
# of Electrons
Gained or Lost
to Form Ion
Negative Ion
(Anion)
Ca +2
Lost 2 electrons
F-1
# of Electrons
Gained or Lost
to Form Ion
Gained 1
electron
Formula for
Ionic
Compound
CaF2
Instructional Tip:
Another column may be added to the chart for naming the compounds.
Part III: Balancing Chemical Equations
6. Write a chemical reaction statement on the board. For example:
Potassium and phosphorus produce potassium phosphide.
7. Have students, working in small groups, select an element card representing potassium
and an element card representing phosphorus. Have them hang the cards on the left side
of a hanger balance to represent the reactants of the reaction. (For a diagram and
complete instructions for construction of the cards and hanger balance, see Attachment D,
Hanger Balance.)
8. Have the students write the formula for potassium phosphide (K3P) and represent the
compound by attaching three potassium cards to one phospide card. Tell them to hang
the compound on the right side of the balance to represent the product of the reaction.
K + P
K3P
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Balancing Chemical Equations – Grade Nine
9. Since the hanger is not balanced, ask the students, “What needs to be done to balance the
reaction (hanger)?” (To level the hanger balance, place three potassium cards and one
phosphorus card on the left side of the balance.)
3 K + P
K3P
10. Have students use the periodic table to find the atomic masses of potassium and
phosphorus and use them to calculate the total mass of the left side of the equation (three
potassium atoms and one phosphorus atom) and the total mass of the right side of the
equation (three potassium atoms and one phosphorus atom).
11. Ask students to explain how the Law of Conservation of Mass is illustrated by this
example.
12. Repeat the process with the reaction of potassium and oxygen.
K + O2
K2O
Remind students that since oxygen is diatomic (occurs as a molecule of two atoms of
oxygen) in nature, it must be constructed by attaching two oxygen cards to each other.
(To balance this reaction, hang four potassium cards and one O2 group on the left side of
the hanger balance and two K2O groups on the right side of the hanger balance.)
4 K + 1 O2
2 K2O
13. Repeat the process with other reactions.
14. As a paper/pencil activity, have students practice balancing a series of equations when
the formulas of the reactants and products are given. See Attachment C, Balancing
Equations Worksheet.
Part IV: Summarizing Concepts
15. Have students construct concept maps illustrating the process by which atoms combine to
form compounds, molecules combine to form more complex compounds and chemical
reactions are balanced. Tell students to use appropriate vocabulary to illustrate and
explain the processes of chemical reactions and bonding.
16. Evaluate students’ understanding of the concepts presented in this lesson and either
proceed to the post-assessment or provide additional practice on either writing formulas
or balancing equations.
Differentiated Instructional Support:
Instruction is differentiated according to learner needs, to help all learners either meet the
intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the
specified indicator(s).
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Balancing Chemical Equations – Grade Nine
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

Allow students to work independently, in pairs or heterogeneous groups to share differing
skills, knowledge and experience in lesson activities.
This lesson is designed to give students hands-on experiences with writing formulas for
compounds and balancing chemical equations including multiple opportunities to
observe, describe and practice concepts learned.
Challenge students to choose examples of reactions to balance that are more complex
because they contain reactants or products such as hydrates or complex ions.
Extensions:
 Have students explore the similarity between Coulomb’s law and the law of universal
gravitation.
 Have students explore reactions involving complex ions.
 Have students write formulas for hydrates.
 Have students classify reactions by type.
Homework Options and Home Connections:
Have students create a game for ion formation, formula writing or equation balancing.
Materials and Resources:
The inclusion of a specific resource in any lesson formulated by the Ohio Department of
Education should not be interpreted as an endorsement of that particular resource, or any of
its contents, by the Ohio Department of Education. The Ohio Department of Education does
not endorse any particular resource. The Web addresses listed are for a given site’s main
page, therefore, it may be necessary to search within that site to find the specific information
required for a given lesson. Please note that information published on the Internet changes
over time, therefore the links provided may no longer contain the specific information related
to a given lesson. Teachers are advised to preview all sites before using them with students.
For the teacher: Pith balls, rubber rod, fur, glass rod, silk, card stock, clothes hangers,
paper clips.
For the students: Jars or vials, silver chloride and sodium chloride, or silver chloride and
sodium bromide, or calcium nitrate and sodium sulfate, plastic wrap, ion
cards, hanger balance, elements cards.
Vocabulary:
 atoms
 molecules
 substances
 cation
 anion
 ionic compound
 ionic bond
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Balancing Chemical Equations – Grade Nine
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


balanced chemical equation
law of conservation of mass
pith ball
Coulomb’s law
Technology Connections:
 Use the Internet to find video clips that show electrostatic forces of attraction and
repulsion.
 Use computer animations to show the process of ion and compound formation.
 Use videos or CD-ROMs to demonstrate a variety of chemical reactions.
Research Connections:
Marzano, R. et al. Classroom Instruction that Works: Research-Based Strategies for
Increasing Student Achievement. Alexandria: Association for Supervision and Curriculum
Development, 2001.
Cooperative learning has a powerful effect on student learning. This type of grouping
includes the following elements:
 Positive interdependence;
 Face-to-face promotive interaction;
 Individual and group accountability;
 Interpersonal and small-group skills;
 Group processing.
Nonlinguistic representations help students think about and recall knowledge. They
include the following:
 Creating graphic representations (organizers);
 Making physical models;
 Generating mental pictures;
 Drawing pictures and pictographs;
 Engaging in kinesthetic activity.
Attachments:
Attachment A, Post-Assessment Rubric
Attachment B, Formula Writing
Attachment C, Balancing Equations Worksheet
Attachment D, Hanger Balance
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Balancing Chemical Equations – Grade Nine
Attachment A
Post-Assessment Rubric
Level 4 Student accomplished the task, recorded thorough observations and correctly
responded to all of the questions.
Level 3 Student accomplished the task, correctly responded to most of the questions but had
one or two errors in writing the correct formulas, predicting the products of the
reaction or balancing the reaction.
Level 2 Student accomplished the task, responded to most of the questions and had multiple
errors in writing the correct formulas, predicting the products of the reaction or
balancing the reaction.
Level 1 Student completed the task but with inaccuracies, partially responded to the
questions and had multiple errors in writing formulas, predicting the products or
balancing the chemical reaction.
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Balancing Chemical Equations – Grade Nine
Attachment B
Formula Writing
Positive
Ion
(Cation)
Ca +2
Number of Electrons
Gained or Lost to
Form Ion
Negative
Ion
(Anion)
Number of Electrons
Gained or Lost to
Form Ion
Formula for
Ionic
Compound
Lost 2 electrons
F-1
Gained 1 electron
CaF2
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Balancing Chemical Equations – Grade Nine
Attachment C
Balancing Equations Worksheet
Balance the following equations:
1. Limestone (CaCO3), a common Ohio mineral, can be heated to produce calcium oxide.
CaCO3  CaO
+ CO2
2. Joseph Priestley discovered oxygen in 1774. He heated mercury (II) oxide to form
mercury and oxygen.
HgO 
Hg + O2
3. Ammonia is an important compound used to make fertilizers. It is produced by reacting
nitrogen and hydrogen.
N2 + H2 
NH3
4. Photosynthesis is a reaction by which plants convert carbon dioxide and water into sugar.
CO2 + H2O 
C6H12O6
+
O2
5. Combustion of gasoline in an automobile engine not only produces carbon dioxide and
water but also energy.
C8H18
+
O2 
CO2
+
H2O
6. Marble (calcium carbonate) reacts with sulfuric acid (one possible acid in acid rain).
+ H2SO4  CaSO4
CaCO3
+
H2O + CO2
7. Iron reacts with oxygen in the air to form rust (Fe2O3).
Fe +
O2 
Fe2O3
8. Magnesium hydroxide (one ingredient in a popular antacid) is used to neutralize stomach
acid.
Mg(OH)2
+ HCl 
MgCl2 +
H2O
9. Silver nitrate and sodium bromide are used to make silver bromide (a sun-sensitive
substance useful in photographic processes).
Ag NO3
+ NaBr 
AgBr
+
NaNO3
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Balancing Chemical Equations – Grade Nine
Attachment C (continued)
Balancing Equations Worksheet
Answers:
1. CaCO3  CaO + CO2
2. 2HgO 
2Hg +
3. N2 + 3H2 
O2
2NH3
4. 6CO2 + 6H2O 
C6H12O6
25O2 
+
6O2
5. 2C8H18
+
16CO2
+
18H2O
6. CaCO3
+ H2SO4  CaSO4
+
H2O + CO2
7. 4Fe + 3O2 
8. Mg(OH)2
9. Ag NO3
2Fe2O3
+ 2HCl 
+ NaBr 
MgCl2 +
AgBr
+
2H2O
NaNO3
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Balancing Chemical Equations – Grade Nine
Attachment D
Hanger Balance
Construct the hanger balance from a hanger and two paper clips. Open the paper clips and
attach one to each end of the hanger. Use masking tape to hold the paper clips in place so
that they do not slide. The element cards are hung on the paper clips.
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Balancing Chemical Equations – Grade Nine
Attachment D (continued)
Hanger Balance
Element / Ion Cards
Construct the element cards from heavy card stock paper. On one side of each card, write the
symbol of the element and on the other side write the symbol for the ion. Punch a hole in the
top center of each element card so that it can be hung on a hook. Attach a different weight
to the back of each element/ion card since different elements have different weights. Use
washers of various sizes and number to serve as weights. Make multiple cards of the same
element. Place dots on the cards to represent the number of electrons the element is
expected to gain or lose when forming compounds. For example, place one dot for
potassium (loses one electron) and two dots for oxygen (gains two electrons). Devise a way
to attach the cards (i.e., paper clips) to each other to represent compounds.
Instructional Tip:
Provide the materials and have students construct their own cards. It provides a good handson activity during the discussions about the number of electrons that atoms are likely to gain
or lose and the law of conservation of mass.
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Balancing Chemical Equations – Grade Nine
Attachment D (continued)
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