chemical dominoes
Section 2
Balancing Chemical Equations
Section Overview
Background Information
In this section, students will refer to the previous
section of generating CO2 gas. They will design
an experiment to determine if mass is conserved
during the chemical reaction in Method 2. They
then connect the conservation of matter to the need
to balance chemical equations. Students learn to
recognize whether a chemical equation is balanced.
Then, they learn to balance simple chemical
equations by an accounting method using the
concept of dominoes. Along the way, they practice
identifying how many of each element there
are in a given formula, which involves reading
parentheses and subscripts properly.
Before students can perform stoichiometry, or
the calculation of quantities of chemical elements
involved in chemical reactions, they must learn
to balance chemical equations. This section will
teach that skill. Students are asked to put their
understanding of the Law of Conservation of
Matter to practice by designing an experiment to
show that matter is conserved in a reaction that
produces a gas.
Conservation of Matter
The concept of conservation of matter mystified
scientists for centuries. A brief historical
perspective is provided in the Chem Talk section
in the Student Edition. The same pervasive
misconceptions that boggled early scientists
still plague students today. Several of these are
identified with sources explained in the Students’
Prior Conceptions section in this Teacher’s Edition.
learning outcomes
learning outcomes
634
Location in Section
Evidence of Understanding
xplain the purpose of
E
balancing a chemical equation.
Chem Essential Questions,
Reflecting on the Section
and the Challenge.
Students’ answers match those found in this
Teacher’s Edition.
elate the balancing of
R
an equation to the Law of
Conservation of Matter.
Chem Talk,
Checking Up
Students can relate the Law of Conservation of Matter
to equation balancing.
Balance a chemical equation.
Investigate
Parts B and C
Chem to Go
Students successfully complete the equation exercises.
SEction 2 balancing chemical equations
chapter 4
Notes
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635
chemical dominoes
Section 2
Materials, Chemicals, Preparation, and Safety
(“per Group” quantity is based on group size of 4 students)
Materials and Equipment
Materials
(and Equipment)
Quantity
per Group
(4 students)
Balloons, high quality latex
1 (Have
additional on
hand)
Beaker, 250-mL
1
Graduated cylinder, 10-mL
1
Erlenmeyer flask , 125-mL
1
Clamp for Erlenmeyer flask
1
Ringstand
1
Resealable storage bag, quart-size
1
Scoopula
1
Weighing boat
1
Bingo markers Color “A”
1 pkg of 50
Bingo markers Color “B”
1 pkg of 50
Materials (and Equipment)
Quantity
per Class
Index cards
50
Balances, 0.01 g
2
Rubber bands (to fit on
250-mL beaker)
636
Chemicals
1 box
Chemicals
Calcium carbonate, CaCO3
Hydrochloric acid (HCl), 1.0 M
(from Section 1)
Quantity
per Class
(24 students)
35 g
100 mL
SEction 2 balancing chemical equations
Part A
• For the materials and equipment required for
Part A, it will save time if you have a set of
materials for each lab group ready ahead of
time in boxes.
Part B
• If your students have had prior experience
balancing equations, you may wish to skip
Part B, and elect to start at Part C, Step 1.
• If your students have had no prior exposure
to balancing equations, you may wish
to photocopy the Blackline Master titled
“Practice with Balancing Chemical Equations.”
Part C
•If you choose, you could provide groups
with their chemical equation on index cards.
A Blackline Master of the equations is
provided. This might prevent confusion as
to which group should be working on which
equation. Each set of three equations (A, B,
C) cards might be written (or printed out and
taped/pasted) on a particular color of index
card, so that each group is color-coded. Or, if
you use all one color (white, for example) of
index cards, you could label each group by a
number, e.g., 1-A, 1-B and 1-C for group 1.
chapter 4
Teacher Preparation
Hand out the index cards to groups at these points:
A – Step 4
B – Step 6
C – Step 7
Group 1
Pb(NO3)2
A
B
lead (II)
nitrate
Pb2+
NO3NH4+
SO42-
Pb(NO3)2
C
lead (II)
nitrate
+
(NH4)2SO4
→
and ammonium yield
sulfate
+
(NH4)2SO4
→
and ammonium yield
sulfate
PbSO4
+
NH4NO3
lead (II) and ammonium
sulfate
nitrate
PbSO4
+
2NH4NO3
lead (II) and ammonium
sulfate
nitrate
Group 2
Cu(NO3)2
A
B
Na3PO4
copper (II) and sodium
nitrate
phosphate
→
Cu3(PO4)2 +
NaNO3
yield copper (II) and sodium
phosphate
nitrate
Cu2+
NO3Na+
PO43-
3Cu(NO3)2
C
+
+
2Na3PO4
copper (II) and sodium
nitrate
phosphate
→
Cu3(PO4)2 +
6NaNO3
yield copper (II) and sodium
phosphate
nitrate
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chemical dominoes
Group 3
A
B
Fe(NO3)3
iron (III)
nitrate
Fe3+
NO3K+
CO32-
2Fe(NO3)3
C
iron (III)
nitrate
AlCl3
+
K2CO3
and potassium
carbonate
+
3K2CO3
and potassium
carbonate
→
yield
→
yield
Fe2(CO3)3 +
KNO3
iron (III) and potassium
carbonate
nitrate
Fe2(CO3)3 +
6KNO3
iron (III) and potassium
carbonate
nitrate
Group 4
A
B
aluminum and chloride
C
+
Pb(NO3)2
→
lead (II)
nitrate
yield
3Pb(NO3)2
→
lead (II)
nitrate
yield
HCl
→
hydrogen
chloride
yield
6HCl
→
hydrogen
chloride
yield
PbCl2
+
Al(NO3)3
lead (II) and aluminum
chloride
nitrate
Al3+
ClPb2+
NO32AlCl3
+
aluminum and chloride
3PbCl2
+
2Al(NO3)3
lead (II) and aluminum
chloride
nitrate
Group 5
Al2(CO3)3
A
B
aluminum and carbonate
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AlCl3
+
H2O
aluminum and water
chloride
+
CO2
and
carbon
dioxide
+
3CO2
and
carbon
dioxide
Al3+
C
O
H
Cl
Al2(CO3)3
C
+
+
aluminum and carbonate
2AlCl3
+
3H2O
aluminum and water
chloride
SEction 2 balancing chemical equations
chapter 4
Group 6
A
B
C
Al(NO3)3
+
K3PO4
aluminum and potassium
nitrate
phosphate
Al3+
NO3K+
PO43-
Al(NO3)3
+
K3PO4
aluminum and potassium
nitrate
phosphate
→
AlPO4
+
KNO3
yield aluminum and potassium
phosphate
nitrate
→
AlPO4
+
3KNO3
yield aluminum and potassium
phosphate
nitrate
Group 7
Ba(NO3)2
A
B
barium
nitrate
Cr2(SO4)3
and chromium (III)
sulfate
→
yield
BaSO4
+
Cr(NO3)3
barium and chromium (III)
sulfate
nitrate
Ba2+
NO3Cr3+
SO42-
3Ba(NO3)2
C
+
barium
nitrate
+
Cr2(SO4)3
and chromium (III)
sulfate
→
yield
3BaSO4
+
2Cr(NO3)3
barium and chromium (III)
sulfate
nitrate
Safety Requirements
• Goggles
and aprons are required in the
laboratory area.
• All
chemicals can be disposed of in the
garbage or drain.
• Wash
arms and hands before leaving the
laboratory area.
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639
chemical dominoes
Meeting the Needs of All Students
Differentiated Instruction
Augmentation and Accommodations
Learning issue
640
Reference
Augmentation and Accommodations
Understanding the
term balance
What Do You
Think?
Accommodations
• In this section, it might work well for students to think about the literary
examples of the term and the two questions that follow before looking at the
art. An analysis of the illustration could serve as a scaffold to help students
think about balance in chemistry.
Design an
experiment and
recording data
Investigate
Part A
Accommodations
•P
rovide an outline of a procedure for students to follow. This could take the
form of topics and subtopics that students fill in. Provide a completed lab
procedure for students who need more of a scaffold.
• Provide students with a partial or complete table for recording their data.
Learning to read and
apply the symbols
used to describe
chemical reactions
Investigate
Parts B and C
Augmentation
• S tudents need direct instruction to learn the symbols which are used to write
the equations of chemical reactions. They will need to learn “coefficient” and
“subscript.” Have students write the definitions in their logs.
•H
ave students write the name of a compound in their logs and label the names
of each element, the coefficients, and subscripts.
•M
odel an example so students can see how the products of coefficients and
subscripts determine the number of atoms of that element. Show them the
impact of parentheses as well.
Accommodations
•G
ive students the rules for finding the number of atoms in a compound to copy
into their logs and have them apply the rules in doing Step 4 of Part C.
Balancing complex
chemical reaction
equations
Investigate
Part B
Augmentation
•A
nticipate students’ difficulties in balancing reactions that involve use of
equivalent multiples. In 2.a) and 2.b), one can determine the coefficients by
simply counting the number of atoms on each side and inserting a matching
coefficient, but in 2.c), students will need to determine a common multiple that
can serve to balance the number of atoms. Students must multiply the oxygen
atoms by a different number on the reactant side (2) than on the product side
(3) to end up with six total oxygen atoms on each side. Most students will
intuitively multiply the subscripts, determine that six is the common multiple,
and determine the coefficients to go with the oxygen. Then, they will need to
adjust the NaCl. Others will need to be given a series of steps that will work for
most equations so they can use the rule to balance complex equations. They
also need to learn persistence in applying these steps since they may not think
the solution will work out before following a number of steps.
• S ome students might benefit from thinking about how to find the lowest
common denominator in adding fractions with unlike denominators.
SEction 2 balancing chemical equations
Reference
chapter 4
Learning issue
Augmentation and Accommodations
Generalizing
concepts from
specific problemsolving experiences
Investigate
Part C, 7.a)
Accommodations
•E
ven students who have been successful balancing the practice problems may
have difficulty making generalizations which apply in every case. One way to
help them is to provide scaffolding questions. What should you do first? Should
they begin with the first element on the left? If the number of atoms of an
element is the same on each side, what comes next? What if one coefficient is
a multiple of the other? What if they are different, but not multiples? What
if one has a subscript greater than one? Once one element is in balance, what
comes next?
• Instead of a list of instructions, ask students to create a flowchart.
Learning vocabulary
Chem Talk
Augmentation
• S tudents must learn the words reactant and product and understand what
“associated with different elements” looks like in equations. Check to see that
all students can identify the reactants, products and associations of elements.
Strategies for Students with Limited English Language Proficiency
Learning issue
Reference
Augmentation and Accommodations
Background
knowledge
What Do You
Think?
Students may need to have extensive background on the quotes at the beginning
of this section. Also, provide discussion on different uses (semantics) of the word,
“balance.”
Vocabulary
Investigate
Students are asked to “design (2)” an experiment and may need some specifics
on how this word is used. It could mean a number of different things depending
on its use. Words such as “visualization (Part B)” and “symbolic” might also be
confusing. Also check for other new words such as, “coefficient” and “analyze.”
Students may not have experienced playing “Bingo” and might not understand
the references.
Background
knowledge
Vocabulary
Comprehending text
Chem Talk
Check for understanding of words such as “conserved.” Some background
information about the Greek philosophers mentioned might be useful in providing
contextual knowledge. Make sure that the term “historically documented” is
correctly interpreted. Some background information about France in the 1700s
may provide more context for understanding Lavoisier’s work.
Supporting details
Research skills
What Do You
Think Now?
Because students will have to refer to the slightly obscure quotes, discuss them in
context of chemistry to improve comprehension. Check for understanding of the
quotations prior to the task. Students can discuss this question with a partner and
the teacher can hold a discussion of the various responses from class members.
Comprehension
Vocabulary
Chem Essential
Questions,
Chem to Go
Students are asked to “explain” as one of their responses in the Nano section and
other parts of this section. They may need concrete directions as to what they
have to do. Students may need help with the pronunciation of “effervescent.”
Check to see that students can correctly decode the formula. Have students
respond in small groups and share consensus answers.
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641
chemical dominoes
Section 2
What Do You Think?
What Do You Think?
Teaching Suggestions
and Sample Answers
a chemist’s response
These are open questions that
will have varied answers. They
should lead to a good discussion.
Students will have a variety
What Do You See?
of ideas about the meaning of
The purpose of this exercise is to
the term “balance.” Most will
engage students’ interest and to
concede that it is dependent
introduce concepts in visual form
upon the context. The purpose
that they will see later in the
of these questions is to stimulate
section. You should not expect
students to realize that words
correct answers at this point.
typically have more than one
The illustration shows a crude
meaning and to show them
balance of weight using chemical
that context is important to
spheres of different weights
determine meaning.
(and colors). The white board
shows a balanced equation using
spheres representing methane
and oxygen as reactants. Carbon
dioxide and water are shown
as products of this combustion
reaction.
Students’ Prior Conceptions
Several misconceptions get in the way of
understanding the concept of conservation of matter.
Other misunderstandings inhibit learning the skill of
balancing chemical equations. Some stumbling blocks
to learning include the following misconceptions:
1. Gases have no mass.
This misconception results from the invisibility of most
gases. The misconception leads many, including most
of the famous scientists before the 18th century, to
conclude that mass is not conserved.
2. Subscripts in chemical formulas are independent of
parentheses.
This is a lack of understanding of how to read chemical
formulas. Since the notations in mathematics and
chemistry differ, this confusion is understandable,
642
In the Duke of Wellington
quotation, “balance” means
“comparison [of battle forces].”
One can imagine a huge two-pan
balance being used to measure
the potential outcome of a battle.
On one pan would be the British
forces; on the other, the French
troops plus Napoleon.
In the Plutarch quotation, a similar
use of “balance” is intended,
but this time the abstract values
or “weights” of friendships are
referred to. The suggestion is that
those friendships that last through
times of adversity are more
valuable, or weigh more, than
those that do not.
In chemistry, the term “balance”
has a more concrete meaning than
in the two literary examples. Taking
the → of any chemical reaction
as the fulcrum of a balance, a
balanced chemical equation has
the same mass of matter on each
side. The atoms are the same
and the numbers of each type of
atom are the same. The words
of Wellington and Plutarch are
related to chemical balance in that
two quantities are compared using
a fulcrum (real or imaginary).
especially for students who are trying to make sense of
algebra at the same time they are learning chemistry.
The best remedy is practice. Visuals help immensely
in illustrating the formulas for those who don’t see
numbers in their heads. For example, try representing a
unit of Pb(NO3)2 as:
O
Pb
O
O
O
N
O
N
O
Pb
=
NO3
NO3
SEction 2 balancing chemical equations
chapter 4
3. All materials provided must be used in an
experiment.
There are many possible designs for an experiment that
provides evidence supporting the conjecture that mass
is conserved in the reaction between calcium carbonate
and hydrochloric acid. More equipment and supplies
are listed than are necessary for any one experiment.
Encourage students to design their experiments first,
and then decide what materials to use.
4. Every experiment must have a hypothesis,
variables, and a control.
This is a carryover from biology, where many
experiments compare two or more processes under
different conditions. Whenever there is a comparison,
something must be varied, and all the other variables
must be kept constant. Also, one must compare the
results to a “control.“ In chemistry, experiments require
hypotheses. However, many experiments do not involve
comparisons when conditions are varied. Therefore,
no control is needed. In the experiment that students
must design here, the hypothesis is that “matter is
conserved.“ Students should try to show that the mass
of the reactants equals the mass of the products.
Active Chemistry
643
chemical dominoes
Investigate
Part A:
Is Matter Really
Conserved?
1.
The students should recognize
the reaction from Section 1,
Method 2, in which CO2
was generated using calcium
carbonate and hydrochloric acid.
Remind students that they may
not need all of the materials
provided.
2.
Students will likely design
an experiment similar to the
procedure used in Method 2 of
Section 1. They will measure
the flask, balloon, chalk, and
hydrochloric acid used. Then,
they will compare this to the
mass of the components after
the balloon has inflated. One
stumbling block they may have
is that they will want to record
the volume of HCl rather than
its mass. Some may see a simpler
method which does not use the
balloon but the resealable plastic
bag. In this method, all that
need be done is to weigh all of
the components going into the
reaction and compare this value
with the mass of the components
in the plastic bag after reaction.
To do this properly, they should
try to keep the HCl away from
the calcium carbonate until the
bag is sealed. To avoid spilling
chemicals on the balance,
caution the students to make
certain that the bag or balloon is
securely sealed.
Check their calculations for
volume of gas generated in the
resealable bag. If much more
644
than 1 quart (1 L) is generated,
the bag may pop open. To
generate 1 L of CO2 gas, 4.4 g
CaCO3 and 88 mL of 1 M HCl
is required. Have the students
work with 1 g or less of CaCO3
and 25 mL of 1 M HCl.
scale. They will have to mass
an empty container and then
add the calcium carbonate to
it. Often, students will list what
they want to measure rather
than what they have to measure.
3.
Observe students as they carry
out their procedures so you can
discuss possible sources of error
with them later.
Check students’ data tables
carefully to be sure they are
recording measurements and not
just calculations. For example,
they will have to know the mass
of the calcium carbonate but
cannot mass it directly on the
4.
a) If students have good lab
technique, their masses before
and after the reaction should
SEction 2 balancing chemical equations
teaching tip
Depending on your students’
familiarity with lab work, this may
be a good stopping point for a
45 minute class period. If students
are progressing more rapidly, they
can continue on to Part B.
Part B: Visualizing
Chemical Formulas and
Balancing Reactions
You may wish to provide
copies of the Blackline Master
titled “Practice with Balancing
Chemical Equations” before
students begin.
4-2a
Blackline Master
1.
All of the formulas can be done
with only two colors of bingo
chips but ideally each atom is
represented by one color and one
bingo chip. This can be done for
every equation with the following
table of numbers and colors.
Equation a.
3 colors with a distribution of
4-4-2
10 chips
Equation b.
2 colors
4-4
8 chips
Equation c.
3 colors
4-4-12
20 chips
Equation d.
5 colors
4-4-2-2-6
18 chips
Equation e.
4 colors
2-4-4-12
22 chips
Equation f.
4 colors
2-4-4-12
22 chips
Equation g.
5 colors
4-6-36-6-12 64 chips*
Equation h.
3 colors
6-16-8
30 chips
Equation i.
3 colors
2-8-8
18 chips
chapter 4
be the same. If their results
are different, engage them in a
discussion of what happened.
Often the mass after the
reaction is less. Common
sources of error include
escaped gas and spilled
reagents, HCl or CaCO3.
If the conventional colors that are associated with each type of
atom could be used, that would be best.
Oxygen – Red, Nitrogen – Blue, Carbon – Black,
Chlorine – Green, Sulfur – Yellow, Hydrogen – White
* For this equation, it might be best to use one chip to
represent the SO42- and the OH ions. This would use four
different colors and a distribution of 4-6-6-12 and a total of
28 chips.
Alternative methods for
balancing chemical reactions
can be used as accommodations
for students who have difficulty
with math (least common
multiples), or who may require
a stepwise approach leading up
to the accounting method.
Two alternatives are offered
here:
Alternative Method #1 for Balancing Chemical Equations
1.a)
1.c)
Provide each group or student with a plastic
baggie containing four different colors of
objects. Have students use the objects to
represent the chemical reaction by placing
the objects on a poster board or a magnetic
board. Instruct them to make a legend to
indicate what each colored object represents
and present their reactions to the class.
Add colored objects to the representations and
have students balance the reactions. Ask them
to explain what they have to do to balance the
reaction and to define the rules governing what
they are and aren’t allowed to do.
Proceed to Step 2 in the Investigate.
1.b)
They should notice that something is not
quite right. The chemical reaction is out of
balance. Ask what it means and have them
write their answers.
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chemical dominoes
Alternative Method #2 for Balancing Chemical Equations
1.a)
Use objects that you can obtain in multiples
to represent each item. For example, if the
reaction is
H2 + O2
→
H2O
you could use pennies to represent H atoms and
nickels to represent O atoms. Other objects that
can be used are dimes, quarters, poker chips, and
any other object that has a consistent mass.
1.b)
Have students represent the equation as
written using the objects. For example, they
would need two pennies and two nickels on
the input side, and two pennies and one nickel
on the output side. When atoms are parts of
molecules, they stack the objects to indicate that
only complete molecules can be added.
teaching tip
Some students have difficulties
distinguishing parts of polyatomic
ions from the polyatomic ions
themselves. With all the numbers,
this can be confusing. It is helpful
to write down what the “item”
is first, and then look to see how
many of them there are. Some
students may benefit from the
extra step of substituting an X for
the “item” – they should only need
to do this a few times before they
internalize it. For example, in 1.c)
when looking for the quantity of
SO4 items, if the item were X, then
the question would read: how
many of the item X are there in
6Al2(X)3? Also, sometimes it
helps to draw one empirical
formula of the compound, then
ask, “How many SO4 (or X) items
would there be in 6 of these?”
So if they need to add more nickels to the
output side, they’ll have to add a complete
water molecule: two pennies and a nickel.
1.c)
Have them add molecules to the input and
output sides until both sides have equal
amounts of every item.
1.d)
To check that the equation is balanced, students
should weigh all the objects on the input side
at the same time and record the mass. They
should then weigh all the objects on the output
side at the same time and record the mass. If
the two masses recorded are equal, then the
equation is balanced and matter is conserved.
Proceed to Step 2 in the Investigate.
2.
Assign a different chemical
equation (a, b, c, d, e, f, g, h, i) to
each group. If you are providing
the equations on index cards, give
a card to each group. Each group
receives a different chemical
equation. Some are more difficult
than others to balance, but all
have polyatomic ions in them.
You may wish to give thought
to which group should receive
which equation. In addition to
illustrating what prior experience
with balancing equations
students have, it also will help
you to identify misconceptions to
students so that you can address
them immediately.
3.a)
You may need to remind students
that polyatomic ions such as
NO3-, OH , and SO42- can be
treated as one bingo marker.
646
Part C:
Using Chemical Symbols
to Balance Equations
1-3.
How much students know
about balancing chemical
equations will become apparent
from their answers to the
questions in these steps.
1.a)
The coefficients are:
1, 2, 1, 1, 1 (all 1’s are not
shown, but understood to be 1)
SEction 2 balancing chemical equations
chapter 4
Active Chemistry
647
chemical dominoes
2.a)
12 O’s
2.b)
2 NO3’s
2.c)
18 SO4’s
2.d)
Some sample rules might be:
I. A subscript next to a symbol
tells you the number of that
specific atom which are
present in one formula unit.
Example: 2KNO3. Oxygen
has a subscript of 3, so there
are 3 oxygen atoms in one
formula unit of KNO3.
II. If the symbol is inside
parentheses, multiply the
subscripts inside and outside
the parentheses to find
the number of that atom
present. Example: Mg(NO3)2.
Multiply the 3 × 2 subscripts
to calculate the correct
number of total O’s in one
formula unit. This is 6.
III. If the formula has a
coefficient in front of it, the
coefficient affects each atom
in the formula. Multiply
the coefficient and subscript
to find the number of an
atom present. Example:
2Mg(NO3)2. The coefficient
of 2 indicates the number
of formula units in the
equation. This coefficient
is multiplied times the two
subscripts to calculate the
total O’s. 2 × 3 × 2 = 12.
3.
Some students who catch on to
the process quickly may find this
step tedious. It is important to
have them do the process slowly
several times in order to avoid
careless mistakes. You can also
give them more challenging
equations and formulas to
balance to help challenge them.
Hand out the index cards to
groups at these points:
648
Equation A – Step 4
Equation B – Step 6
Equation C – Step 7
4.
Answers will vary based on
which equation was assigned.
You can decide if you want
students to separate the elements
composing a polyatomic ion if
the ion reacts as a group.
SEction 2 balancing chemical equations
5.
5.a-b)
Answers will vary according
to the equation that they are
working on.
6.a-c)
Group 1
Atom/Ion
Reactant
Pb
1
NO3
Group 5
Product
Atom/Ion
Reactant
1
Al
2
1
2
1
C
3
1
NH4
2
1
O
9
3
SO4
1
1
H
1
2
Cl
1
3
5.c)
No, there are different numbers
of atoms.
6.
At this point, it is important that
students make a group of the
correct number of atoms in the
chemical formula and use the
coefficient to make the correct
number of groups. The way
in which they connect atoms
in the formulas is not of great
concern at this point. If you have
introduced chemical formulas,
you might point out to students
that positive and negative ions
would be attracted to one
another, so they would alternate
within the compound. Colors
may vary, but should remain
consistent within a particular
part of the question.
Product
Group 6
Group 2
Atom/Ion
Reactant
3
Al
1
1
2
1
NO3
3
1
Na
3
1
K
3
1
PO4
1
2
PO4
1
1
Atom/Ion
Reactant
Cu
1
NO3
Product
Group 3
Atom/Ion
Reactant
Fe
1
NO3
chapter 4
Students should continue
to work with their assigned
equation.
Product
Group 7
Product
Atom/Ion
Reactant
Product
2
Ba
1
1
3
1
NO3
2
3
K
2
1
Cr
2
1
CO3
1
3
SO4
3
1
Group 4
Atom/Ion
Reactant
Product
Al
1
1
Cl
3
2
Pb
1
1
NO3
2
3
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649
chemical dominoes
6.d)
Check to make certain that the
students understand the process.
6.e)
Group 1
Atom/Ion
Reactant
Product
Pb
1
1
NO3
2
2
NH4
2
2
SO4
1
1
Group 2
Atom/Ion
Reactant
Product
Cu
3
3
NO3
6
6
Na
6
6
PO4
2
2
Group 3
Atom/Ion
Reactant
Product
Fe
2
2
NO3
6
6
K
6
6
CO3
3
3
Group 4
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Atom/Ion
Reactant
Product
Al
2
2
Cl
6
6
Pb
3
3
NO3
6
6
6.f)
Group 5
Product
When an equation is balanced,
the same number of each atom
will appear on both sides of
the equation. Conservation of
matter is observed.
Atom/Ion
Reactant
Al
2
2
C
3
3
O
9
9
H
6
6
7.a)
Cl
6
6
Answers will vary but should
be a more sophisticated version
of 2.d). It is important to check
and make certain each group
has come up with a viable list
of instructions.
Group 6
Atom/Ion
Reactant
Product
Al
1
1
NO3
3
3
K
3
3
PO4
1
1
Group 7
Atom/Ion
Reactant
Product
Ba
3
3
NO3
6
6
Cr
2
2
SO4
3
3
SEction 2 balancing chemical equations
chapter 4
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651
chemical dominoes
Chem Talk
Students learn about the Law of
Conservation of Matter and its
development throughout history.
Checking Up
1.
Matter cannot be created or
destroyed, it can only change
form. Look for reasonable
explanations.
2.
The atom.
What Do You Think
Now?
This is an appropriate time
to revisit the What Do You
Think? questions. Students
may conclude that the literary
connotation of “balance” as
contained in the quotations has
no relationship with the scientific
term “balanced equation”
meaning that the same numbers
and types of atoms are present
on each side of an equation.
Providing them with the answers
contained in A Chemist’s
Response may generate some
discussion and an opportunity to
reconsider or share views. You
may also want to return to the
What Do You See? illustration
to see if students are able to
make more connections with the
science they have just learned.
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Chem Essential
Questions
What does it mean?
MACRO — If students’
experiments in Part A supported
the Law of Conservation of
Matter, they should indicate that
the amount of matter (mass) of
the starting materials equaled
the amount of matter (mass) of
the ending materials. If their
experiment did not support the
law, they might describe their
likely sources of error to explain
why their results were different.
NANO — The equation is balanced
because the same number of atoms
of each element appear on the
reactant and product side of the
equation.
How do you know?
The gas would have escaped and
the mass of the ending materials
(products) would be less than that
of the starting materials (reactants).
However, the Law of Conservation
of Matter is still true. The matter
was not destroyed but the
experimental design did not allow
for the mass of all the products to
be measured.
SEction 2 balancing chemical equations
chapter 4
Why do you believe?
The law appears to be violated
because the mass before and after
reaction are not the same. However,
the equipment did not allow all
of the matter to be collected and
weighed. If the experiment were
designed to allow the evolved gas to
be collected and weighed, the Law of
Conservation of Matter would have
been confirmed by data.
SYMBOLIC —
CaCO3
CaO
+
Why should you care?
If a gas is to be generated as a
part of the Chemical Dominoes
Challenge, it would be important
to calculate how much gas is
needed. For example, blowing up a
balloon to a given size will require
a specific amount of gas.
CO2
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653
chemical dominoes
Reflecting on the
Section and the
Challenge
Students should read this
section for a specific, direct
connection between the section
and the Chapter Challenge.
While students do not answer
any questions in this section,
it will provide them with
valuable direction in the Chapter
Challenge. You may want to
provide some class time for
students to read this paragraph
silently or aloud.
Chem to Go
1.
Equation a) is balanced,
equation b) is not. You can tell
by comparing the quantities of
different atoms on each side
of the arrow. In a balanced
equation, every item must
balance. For example, in
equation a), there are a total
of 14 O atoms on the left, and
(8+6=) 14 on the right.
In b), while the Mg atoms are
balanced, the O atoms are
not: (6+4=) 10 on the left and
(8+1+4=) 13 on the right. The
SO4 units are not balanced
either. The correct balanced
equation is:
MgCO3 + H2SO4
→
MgSO4 + H2O + CO2
2.
The Ca salts should not have
3 as a coefficient. The correct
equation is:
2AgNO3 + CaCl2
Ca(NO3)2 + 2AgCl
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→
3.
4.
This chemical equation must
be wrong because on the input
side there are Na, SO4, Ba and
Cl, but on the output side the
Na is missing. Matter cannot be
conserved as written. The correct
equation is:
The elements that must be on the
output side are the same as the
ones on the input side: K, Mn,
O, and I.
Na2SO4 + BaCl2
2NaCl + BaSO4
→
SEction 2 balancing chemical equations
5.
→
a)
2Na + Cl2
b)
C3H8 + 5O2
c)
MgCO3 + 2HBr
d)
2AgNO3 + CaCl2
e)
2KClO3
f)
3Cu(NO3)2 + 2Fe
→
Coefficients (in order) are:
2-1-2
2NaCl
→
3CO2 + 4H2O
1-5-3-4
→
1-2-1-1-1
MgBr2 + CO2 + H2O
→
2AgCl + Ca(NO3)2
2KCl + 3O2
→
chapter 4
The correctly balanced equations are:
2Fe(NO3)3 + 3Cu
2-1-2-1
2-2-3
3-2-2-3
Notes
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655
chemical dominoes
6.a)
7.
9.a)
The difference is that Mg(OH)2
means there is one Mg and there
are two OH’s, while MgOH2
means there is one Mg, one O,
and two H’s.
The elements that must be in
the white solid are O, K and Cl,
because the ending materials are
oxygen gas (contains O) and
potassium chloride (contains K
and Cl), so all of these must have
been in the single white solid
that was the starting material.
The compound is KClO3.
The coefficients are all the
numbers in front of the chemical
formulas (3, 2, (1), 3) , the
subscripts are all the numbers
within the chemical formulas
(2, 4, (1) 2, 4, 3, 2). When the
coefficient or the subscript is 1, it
is not written, but understood to
be 1, as in Al.
8.
9.b)
The reaction can be illustrated as:
The coefficients are the numbers
you are allowed to adjust when
balancing an equation.
6.b)
The correct one to replace
the X is Mg(OH)2. You can
tell because there are two O
atoms on the product side of
the equation. Using MgOH2
would only provide one O on
the reactant side of the equation.
In addition, there is no such
compound as MgOH2.
metal + solution →
lead chloride + hydrogen gas
The only metal on the output
side is lead, so the metal on the
input side must be lead (Pb).
Pb + 2HCl
→
PbCl2 + H2
10.
b) Fe2O3
11.
d) PCl5
→
PCl3 + Cl2
12.
b) C2H6
Section 2 – QUiz
4-2b
Blackline Master
1. Explain why it is important to balance chemical equations.
2. Indicate how many of each kind of element are in the following chemicals.
Example: H2O has two H atoms and one O atom
a) CaBr2 has ______________________________________________________________________
b) H2SO4 has _____________________________________________________________________
c) AgNO3 has _____________________________________________________________________
d) (NH4)2SO4 has _ ________________________________________________________________
3. The following chemical equations are not balanced. Balance them.
Show your work below or on separate paper.
→ H2O when balanced is 2H2 + O2 → 2H2O
a) HCl + MgCO3 → MgCl2 + H2O + CO2 when balanced is ___________________________
b) Zn + AgNO3 → Zn(NO3)2 + Ag when balanced is _________________________________
Example: H2 + O2
4. Which equation shows a conservation of mass?
656
→ H2 + O2
c) CaCO3 → CaO + CO2
a) H2O
→ AgCl
→ KCl + O2
b) Ag + Cl2
d) KClO3
SEction 2 balancing chemical equations
chapter 4
Section 2 – QUIZ ANSWERS
❶It is important to balance chemical equations to show how matter is conserved and also to
allow for stoichiometric calculations, which must be based on balanced equations.
❷a) CaBr2 has one Ca and two Br’s
b) H2SO4 has two H’s, one S and four O’s
c) AgNO3 has one Ag, one N and three O’s
d) (NH4)2SO4 has two N’s, eight H’s, one S and four O’s
❸
a) 2HCl + MgCO3
→ MgCl2 + H2O + CO2
b) Zn + 2AgNO3
→
❹
c) CaCO3
→
Zn(NO3)2 + 2Ag
CaO + CO2
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