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First Investigation of Chemical
Change
What happens when soda water
loses its fizz?
Two Questions about Chemical Change
• What is a chemical change?
– A change in matter where atoms are rearranged into new
molecules.
• Two questions that scientists always try to answer
about chemical changes that involve carbon atoms:
– The Movement Question: Where atoms moving? (Where
are atoms moving from? Where are atoms going to?)
– The Carbon Question: What is happening to carbon
atoms? (What molecules are carbon atoms in before the
process? How are the atoms rearranged into new
molecules?)
Answering the questions for a simple
chemical change: Soda water losing its fizz
What are your ideas?
•The Movement Question:
Where atoms moving? (Where
are atoms moving from?
Where are atoms going to?)
•The Carbon Question: What
is happening to carbon
atoms? (What molecules are
carbon atoms in before the
process? How are the atoms
rearranged into new
molecules?)
What happens when soda water
loses its fizz?
Where are atoms moving from?
Where are atoms moving to?
Chemical change
What molecules are carbon atoms in before the change?
What other molecules are involved?
What molecules are carbon atoms in after the change?
What other molecules are involved?
Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)
What Are Your Ideas?
Where are atoms moving?
1.
What is happening to
carbon atoms?
1.
Using Tools for Investigation: Digital
Balance
What do these things
weigh?
• A large paper clip
• An empty Petri dish
• Your cup of BTB
solution
• A pencil
(Each member of your
group should weigh one
object.)
Using Tools for Investigation
What does your breath do
to BTB solution?
•Use the soda straw to
blow gently through the
BTB solution.
•What change do you see?
•What substance in your
breath might be causing
this change?
Possible BTB Colors
Comparing Group Results
What weights did each
group find?
• A large paper clip
• An empty Petri dish
• Your cup of BTB solution
• A pencil
How different are your
results?
Why do you think they are
different?
• What changes did you see
in the BTB solution?
• How were the group
results alike or different?
• What substance in your
breath might be causing
this change?
Making Predictions
Predicting mass changes
• What materials will gain
and lose mass when soda
water loses its fizz?
• How are the mass
changes connected with
The Movement Question:
Where are atoms
moving?
• Use arrows on the
worksheet to show your
ideas
Predicting BTB changes
• How will the gas in the
bubbles from soda water
change BTB?
• How are the BTB changes
connected to The Carbon
Question: What is
happening to carbon
atoms?
• Explain your ideas on the
worksheet.
Planning the Investigation
• How will you measure
mass changes?
• How will you observe
changes in the color of
BTB?
Let’s do the investigation!
• What mass changes do
you observe?
• What changes in BTB do
you observe?
• Wait at least 20 minutes
to observe your results.
Discussing Predictions and
Explanations
Predicting mass changes
• What materials will gain
and lose mass when soda
water loses its fizz?
• How are the mass
changes connected with
The Movement Question:
Where are atoms
moving?
• Use arrows on the
worksheet to show your
ideas
Predicting BTB changes
• How will the gas in the
bubbles from soda water
change BTB?
• How are the BTB changes
connected to The Carbon
Question: What is
happening to carbon
atoms?
• Explain your ideas on the
worksheet.
Possible BTB Colors
Comparing Group Results
Results for mass changes
• What patterns are there
in measurements made
by all the groups?
• Do the patterns match
your predictions?
Results for BTB changes
• What patterns are there
in observations made
by all the groups?
• Do the patterns match
your predictions?
Results for Ms. Hach’s Class
Initial
mass of
soda
Group water
Name
(g)
1
30.64
2
50.22
3
43.4
4
32.61
5
43.26
6
34.11
Final
mass of
soda
water
(g)
30.55
50.13
43.3
32.47
43.19
34.03
Change
in mass
of soda start
water
BTB end BTB
(g)
color
color
-0.09 greenish yellow
-0.09 greenish yellow
-0.10 greenish yellow
-0.14
blue
yellow
-0.07
blue
yellow
-0.08
blue
yellow
• How do your results compare with the results for
Ms. Hach’s class?
Explaining Group Results
Explaining results for mass
changes
• How are the mass
changes connected with
The Movement
Question: Where are
atoms moving?
• What unanswered
questions do you have?
Explaining results for BTB
changes
• How are the BTB
questions connected to
The Carbon Question:
What is happening to
carbon atoms?
• What unanswered
questions do you have?
How Atoms Bond Together in
Molecules
• Atoms in stable molecules always have a
certain number of bonds to other atoms:
– Carbon: 4 bonds
– Oxygen: 2 bonds
– Hydrogen: 1 bond
• Oxygen atoms do NOT bond to other oxygen
atoms if they can bond to carbon or hydrogen
instead.
Making the Reactant Molecules:
Carbonic Acid
The “fizz” and the taste of soda water come from carbonic
acid: H2CO3. Make a molecule of carbonic acid on the
reactant of your Molecular Models poster:
1.Get the atoms you will need to make your carbonic acid
molecule. Can you figure out from the formula for carbonic
acid how many C, H, and O atoms you will need?
2.Use the bonds to make a carbonic acid molecule.
Remember the rules for making stable molecules! (Hint: you
will need to make one double bond to make a stable
molecule.)
3.Compare your molecules to the pictures on the next slide.
Are they the same?
Photo of reactant molecules: H2CO3 (carbonic acid)
Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.
Chemical change
Reactants
Products
Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)
Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)
Rearranging the Atoms to Make Product
Molecules: Carbon Dioxide and Water
Soda water loses its “fizz” when carbonic acid (H2CO3)
breaks down into carbon dioxide (CO2) and water (H2O).
Show how this can happen:
1.Break some of the bonds in your carbonic acid molecule
and rearrange the atoms to make two new molecules:
CO2 and H2O. Remember the rules for making stable
molecules! (Hint: you will need double bonds to make
stable molecules of CO2.)
2.Remember, atoms last forever. So you can make and
break bonds, but you still need the same atoms.
3.Compare your molecules to the pictures on the next
slide. Are they the same?
Photo of product molecules CO2 and H2O (carbon dioxide and water)
Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.
Chemical change
Reactants
Products
Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)
Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)
Comparing photos of reactant and product molecules
Start by making the molecules and energy units of the reactants and putting them on the reactants side, then rearrange the atoms and energy units to show the products.
Chemical change
Reactants
Products
Remember: Atoms last forever (so you can rearrange atoms into new molecules, but can’t add or subtract atoms)
Energy lasts forever (so you can change forms of energy, but energy units can’t appear or go away)
Writing a Chemical Equation
• Chemists use chemical equations to show how atoms of
reactant molecules are rearranged to make product
molecules
• Writing the equation in symbols: Chemists use an arrow to
show how reactants change into products:
[reactant molecule formulas] product molecule formulas]
• Saying it in words: Chemists read the arrow as “yield” or
“yields:”
[reactant molecule names] yield [product molecule names]
• Equations must be balanced: Atoms last forever, so
reactant and product molecules must have the same
number of each kind of atom
• Try it: can you write a balanced chemical equation to show
the chemical change when soda water loses its fizz?
Chemical equation for soda
water losing its fizz
H2CO3  H2O + CO2
(in words: carbonic acid yields water
and carbon dioxide)
How can you answer the Movement
Question and the Carbon Question now?
• The Movement Question:
Where atoms moving?
(Where are atoms moving
from? Where are atoms
going to?)
• The Carbon Question:
What is happening to
carbon atoms? (What
molecules are carbon
atoms in before the
process? How are the
atoms rearranged into
new molecules?)