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May 20, 2013
6:30 p.m. – 8:00 p.m. Eastern time
Chemical Change – Introducing a Free
Online Resource for Middle School
Chemistry
Presented by: James Kessler
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Introducing today’s presenter…
Introducing today’s presenters
James Kessler Manager, K-8 Science Education
American Chemical Society
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Assisting in the chat:
Patti Galvan Program Manager, K–8 Science Education
American Chemical Society
American Chemical Society
Middleschoolchemistry.com Big Ideas about the Very Small
Chapter 6: Chemical Change
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Welcome
Free online resource for teaching
basic concepts in chemistry at the
middle school level.
Six chapters of activity-based lesson
plans which align with state standards
in physical science and inquiry.
Two main goals:
• Help students understand common
every day observations on the
molecular level.
• Help students to design and
conduct scientific experiments.
What is middleschoolchemistry.com?
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What’s in a Chapter?
• Lesson Plans (5E):
– Hands-on activities
– Student Activity Sheets
– Multimedia
– Extra Teacher Background
• Student Reading
• Test Bank
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Goals of the Webinar
• Demonstrate selected activities and
animations from the lessons in Chapter 6
to show how they can be used with
students
• Review some basic chemistry concepts
covered in the lessons
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Big Idea for Chapter 6:
Have never
thought about it
and happy that
way
Willing to listen if
it doesn’t take too
long
Stay up nights
pondering this
What happens on the molecular level, during a chemical reaction, that
makes reactants turn into products?
Use the “Fascination Number Line” to indicate your level of
fascination with this question.
0 10 5
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Lesson 6.1 What is a Chemical Reaction?
Extend Explore Explain Evaluate Engage
Is a burning candle a chemical reaction?
As a demonstration, light a candle and tell students that
in a chemical reaction:
• substances combine and react to create something
new.
• the substances that combine are called the reactants.
• the substances that are made are called the
products.
Ask students if they think a burning candle is a chemical
reaction and if they can guess what the reactants are.
Give them a hint by placing a jar over the candle.
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Methane Reacting with Oxygen Extend Explore Explain Evaluate Engage
The reactants are wax from the
candle and oxygen from the air.
The wax is a long chain of carbon
and hydrogen atoms and is called
a hydrocarbon.
The smallest hydrocarbon is
methane (CH4) which we can use
to make a model of the reaction.
The methane reacts with oxygen
and becomes carbon dioxide and
water.
But how did the methane and
oxygen become carbon dioxide
and water?
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Breaking and Making Bonds Extend Explore Explain Evaluate Engage
In a chemical reaction, the bonds between
the atoms in the reactants break.
The atoms rearrange and bond to form the
products.
The products are different substances than
the reactants, but they are made up of the
same atoms, just bonded in different
arrangements.
Explain the subscripts and coefficients.
You can count the atoms on both sides of
the equation and see that they are the same
type and the same number.
This is a balanced chemical equation.
Balanced Chemical Equations
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Extend Explore Explain Evaluate Engage
On the Activity Sheet:
Have students count and
record the number of atoms in
the reactants and products.
They will see that there are
the same number of each
type of atom in the reactants
and the products.
What Does a Chemical Equation Tell You?
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If the chemical equation needs
to be balanced, why can’t it be
written like the second one?
The chemical equation shows
the molecules of the reactants
and the actual molecules they
turn into as products.
How am I supposed to predict or
know what the products will be?
You don’t need to. The reactants
and products will be included.
You just need to interpret what it
means.
What Does a Chemical Equation Mean?
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The equation shows how many of one
molecule reacts with how many of
another to produce how many of each
type of molecule in the products.
In a reaction between methane and
oxygen, one molecule of methane reacts
with two molecules of oxygen.
In this reaction, they always react in the
ratio of 1:2. One molecule of methane
with two molecules of oxygen. Or 100
molecules of methane with 200
molecules of oxygen.
Will an equation be balanced if there is a
lot more of one reactant than another in a
particular reaction?
6.2 - Controlling the Amount of Products in a Chemical Reaction
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As a demonstration, add vinegar to
baking soda and ask students if
this is probably a chemical
reaction.
Yes, because the reactants were a
liquid (vinegar) and a solid (baking
soda) and a gas was produced.
The product, carbon dioxide gas
(CO2), is chemically different from
the reactants.
Controlling the Amount of Products
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Do another demonstration with 10
milliliters of vinegar, 1 drop of
detergent solution, and ½
teaspoon of baking soda to show
a rough measure of the amount of
carbon dioxide produced.
Challenge students to combine
amounts of vinegar and baking
soda to make a foam that
reaches the top but does not
overflow.
Discuss idea that both reactants
are necessary: that lots more of
one will not necessarily produce
more product.
6.3 - Forming a Precipitate
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As a demonstration, combine a
sodium carbonate solution with a
magnesium sulfate (Epsom salt)
solution.
The clear colorless solutions
combine to make a white
precipitate. Ask students if they
think this is a chemical reaction.
Yes, because the products are
different than the reactants. The
magnesium carbonate is the white
precipitate.
NaCO3 + MgSO4 → MgCO3 + NaSO4
Sodium
carbonate Magnesium
sulfate
Magnesium
carbonate
Sodium
sulfate
Making a Chalk Precipitate
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Students make a calcium chloride
solution and sodium bicarbonate
solution and combine them.
A gas is produced and a precipitate
is formed. The precipitate is calcium
carbonate which is the substance
that makes up chalk, egg shells and
sea shells.
Chat Discussion and Questions
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Have you done chemical change activities
similar to these ones?
Have you used them to help kids see that the
equation for the reaction is balanced?
Do you have any questions?
6.4 – Temperature Affects the Rate of a Reaction
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As a demonstration, place one glow stick
in hot water and another identical glow
stick in cold water.
Explain that a glow stick contains two
reactants that mix when you bend and
break the little vial inside.
Ask students:
If the reactants in one glow stick are
cooled and the reactants in another glow
stick are heated, which do you think will
be brighter? Why?
6.4 – Temperature Affects the Rate of a Chemical Reaction
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Ask students how they could design an
experiment to see if temperature
affects the rate of the chemical reaction
they did using calcium chloride and
sodium bicarbonate solutions.
• Use two sets of solutions.
• Heat one set and cool the other.
• Pour the cooled reactants together
and the heated reactants together at
the same time.
See which one foams and forms a
precipitate the fastest.
6.5 – A Catalyst Increases the Rate of a Reaction
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Hydrogen peroxide (H2O2)
decomposes very slowly to form
oxygen (O2) and water (H2O).
The process can be speeded up
tremendously by adding yeast to the
hydrogen peroxide.
This works because yeast contains
a catalyst which catalyzes the
decomposition of the hydrogen
peroxide.
Speeding Up a Chemical Reaction
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A piece of aluminum foil is placed in a
copper II sulfate solution.
No reaction is observed.
Salt is added and a reaction takes place.
One theory is that the salt compromises
a protective coating on the aluminum
which allows the copper II sulfate and
aluminum to react.
In this reaction, electrons leave the
aluminum and join the positively
charged copper ions (Cu2+) making
neutral copper atoms or copper metal.
Hydrogen gas is also produced.
6.6 – Using Chemical Change to Identify an Unknown
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As a demonstration, place two
similar-looking white powders
(baking soda and corn starch) in
two separate cups.
Tell students that you are adding
the same solution (dilute tincture
of iodine) to both cups.
One solution will remain the
original light brown but the other
will turn a very dark purple.
Ask students if the powders were
the same or different. How do
they know?
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Testing the Powders Can chemical change be used to identify an unknown?
Students will test four similar-looking
white powders (baking powder,
baking soda, cream of tartar, and
corn starch) with four different liquids
(water, vinegar, dilute tincture of
iodine, and universal indicator) to see
the reactions, if there are any.
Show students the testing sheet and
ask how the testing should work.
After observing and recording any
reactions, students will test an
unknown powder with the four liquids
to see if the reactions of the unknown
match the reactions of any of the
known powders.
6.7 – Energy Changes in Chemical Reactions
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Students place 10 milliliters of vinegar in a
cup and add a thermometer.
After recording the initial temperature,
students add ½ teaspoon of baking soda
and watch the thermometer.
Why does the temperature go down?
Endothermic Reaction
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We know that in a chemical reaction,
the bonds of the reactants are broken,
atoms rearrange and bond in new
ways to form the products.
It takes energy to break the bonds of
the reactants.
Energy is released when new bonds in
the products are formed.
If it takes more energy to break the
bonds of the reactants than is
released when the bonds of the
products are formed, the reaction is
endothermic.
Calcium Chloride and Sodium Bicarbonate Solutions
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Students place 10 milliliters of baking
soda solution in a cup and add a
thermometer.
After recording the initial temperature,
students add ½ teaspoon of calcium
chloride and watch the thermometer.
Why does the temperature go up?
Exothermic Reaction
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If more energy is released when the
bonds of the products are formed
than was used to break the bonds
of the reactants, the reaction is
exothermic.
Conversions Between Kinetic and Potential Energy
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The energy changes in endothermic and exothermic
reactions are really conversions between the kinetic
energy (KE) of motion and the potential energy (PE) of
attraction.
In bond-breaking, KE is used to break the bonds between
atoms, so KE goes down. But if KE goes down and atoms
are separated, the PE goes up.
So bond-breaking always converts KE to PE and is
endothermic.
Then, when the newly-separated atoms attract each other
and bond, the PE goes down. But if the PE goes down,
the KE has to go up.
So bond-making always converts PE to KE and is
exothermic.
The sum of these energy conversions determines whether
the overall reaction is net endothermic or exothermic.
Energy Diagrams
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Endothermic and exothermic reactions
can also be modeled using energy
diagrams.
Kinetic energy is used to break bonds
between atoms in reacting molecules.
This converts KE to PE.
The atoms rearrange and bond again.
This converts PE to KE.
The difference between these processes
determines whether the reaction is net
endothermic or net exothermic.
Acids, Bases, and pH
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Many chemical reactions involve changes in
pH. What is pH?
A small fraction of water molecules naturally
interact to produce H3O+ and OH- ions.
pH refers to the concentration of H3O+ ions.
Because of the units used to measure pH, as
the concentration of H3O+ ions increases, the
number on the pH scale decreases.
A solution with a pH of 4 (acid) has a greater
concentration of H3O+ ions than a solution
with a pH of 6 (base).
6.8 - pH and Color Changes
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Demonstrate the color changes when
universal indicator is added to citric
acid and sodium carbonate.
Students test different concentrations
of citric acid and sodium carbonate to
try to get as many different colors as
possible.
Adding an Acid or a Base to an Indicator
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An acid is a proton donor. An acid
donates a proton to water creating more
H3O+ ions. These protons can be
transferred to the indicator, resulting in
a color change.
A base is a proton acceptor. A base
accepts protons from water which
makes more OH- ions. Protons are then
transferred from H3O+ ions and from the
indicator to the OH- ions, resulting in a
color change.
Ready to Try it?
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Any final questions?
What content or activities would be useful to you in your classroom?
Thanks to today’s presenter!
Introducing today’s presenters
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James Kessler Manager, K-8 Science Education
American Chemical Society
Assisting in the chat:
Patti Galvan Program Manager, K–8 Science Education
American Chemical Society
Thank you to the sponsor of
tonight’s web seminar:
This web seminar contains information about programs, products, and services
offered by third parties, as well as links to third-party websites. The presence of
a listing or such information does not constitute an endorsement by NSTA of a
particular company or organization, or its programs, products, or services.
Thank you to the sponsor of tonight’s web seminar—1 of 6
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Thank you to NSTA administration—2 of 6
National Science Teachers Association
David Evans, Ph.D., Executive Director
Zipporah Miller, Associate Executive Director, Conferences and Programs
NSTA Web Seminar Team
Al Byers, Ph.D., Assistant Executive Director, e-Learning and Government Partnerships
Brynn Slate, Manager, Web Seminars, Online Short Courses, and Symposia
Jeff Layman, Technical Coordinator, Web Seminars, SciGuides, and Help Desk
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