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2018
Name:
Kendall Hill
Date:
April
21
, 2020
Student Exploration:
Chemical Changes
Vocabulary
:
acid, base, catalyst,
chemical change
,
coefficient, conservation of
matter
,
decomposition, dissolve,
double replacement, endothermic
, exothermic, indicator,
ion,
physical
change,
product, reactant, single replacement, subscript, synthesis
Prior Knowledge Q
uestion
s
(Do th
ese
BEFORE using the Gizmo.)
1.
A student mixes baking soda and vinegar in a
glass
. The
results
are
shown
at
left
. Do you think any new substances are being
created
in this mixture
? If so,
how do you
know?
When these two substances are combined
they form two
chemical reactions b
ecause one is a base and one is an acid.
At the end of the reactions, the bubbles that are shown in the
image are made of carbon dioxide gas.
2.
Suppose
this was
done on
top of
a balance. Do you think the
mass would change as the reaction proceeded?
I
think the mass would remain the same as the reaction proceeds
as long as the amounts are
the same.
3.
What do you think would happen to the mass if the reaction took place inside a
sealed
plastic bag?
The mass would be contained and compressed if the reactio
n were to occur inside a sealed
plastic bag because it was limited room to react in.
Gizmo Warm
up
A
chemical
change
,
(or
chemical
reaction
)
occurs
when one
or more substances, called
reactants
, are transformed into
different substances, or
products
. In the
Chemical Changes
Gizmo, you will look for evidence of chemical
changes
by
looking at changes
you can see, touch, or smell.
To begin, check that
Reactant 1
is
Sodium
and
Reactant 2
is
Water
. Sodium
is a metal so soft you can cut it with a knife.
1.
Click
Play
(
).
What do you observe?
2018
Some type of reaction occurs making a sizzle noise and the water changes
pigmentation to
a clear/glassy color. (releases/forms a vapor too)
2.
Do you think a chemical reaction has taken place? Explain.
Sodium
metal
reacts rapidly with
water
to form a colorless solution of
sodium
hydroxide
(NaOH) and hydrogen gas (H
2
). The resulting solution is basic because of the dissolved
hydroxide. The
reaction
is exothermic.
Activity A:
Observing
chemical changes
Get the Gizm
o ready
:
Click
Reset
(
)
. Check that the reactants are still
S
odium
and
W
ater
.
Turn on the
Label reactants
checkbox.
Introduction:
It is important to distinguish
chemical
changes
,
in which
new substances
are
formed
, from
physical changes
, which do not
create new substances. In this activity, you will
look at
many
kinds of evidence that chemists use to see if a chemical change has taken place.
Question:
What kinds of evidence indicate a chemical
change
has taken place?
1.
Observe
:
Some chemical reaction
s
release
heat, and others absorb heat.
In an
exothermic
reaction, heat is released and the temperature of the system rises. In an
endothermic
reaction, heat is absorbed and the temperature of the system decreases.
In the Gizmo, drag the
Thermometer
into the flask of water.
A.
What is the starting temperature?
21
C
B.
Click
Play
, and wait for the reaction to end. What is the final temperature?
59C
C.
Was this reaction exothermic or endothermic
?
Exothermic (temp rises)
2.
Observe
: Two families of chemicals are
acids
and
bases
. Acids and bases can be detected
by an
indicator
, which is a substance that changes color in the presence of an acid or a
base. Phenol red is an indicator that is yellow in an acid, orange in a neutral
soluti
on, and
pink in a base.
A.
Click
Reset
. Drag the
Phenol red
next to the flask of water. What does the indicator
show?
“Start pH: Neutral”
B.
Click
Play
, and wait for the reaction to
end
. What does the indicator show now?
“End pH: Basic”
3.
Observe
:
Click
Reset
. Select the
Gas collection
setup.
Chemists use this apparatus to
collect any gases produced in the reaction. From the reaction flask, gases
travel
through a
long tube and into a cylinder of water. As gases bubble into the cylinder, the
water is
displaced
(removed)
until the cylinder is filled with gas.
2018
Click
Play
and observe the cylinder. Was any gas produced in the reaction?
How do you know?
Yes, gas was produced when the reaction occurred because it was
visible and audible.
(Activity A continued on
next page)
Activity A (continued from previous page)
4.
Analyze
: One way to
test what
kind of gas is in the cylinder is to
use a glowing splint
.A
glowing splint is a wooden stick that has been lit on fire and then blown out,
resulting in a
glowing, red
h
ot tip. The table shows how a glowing splint reacts to
some
common
gases:
Gas
:
Carbon dioxide
(CO
2
)
or ammonia
(NH
3
)
Oxygen
(O
2
)
Hydrogen
(H
2
)
Splint reaction:
Goes out
Burns brightly
Small explosion and
“pop” sound
A.
Drag the glowing splint next to the
cylinder, and observe. What do you see?
I see that the glowing splint causes a small explosion.
B.
Based on the table above, what gas do you think was produced in this reaction?
The gas produced was Hydrogen (H
2
) according to the table.
5.
Interpret
:
Turn on
Show chemical equation
. A chemical equation is a shorthand way to
describe a chemical reaction.
Symbols
represent the elements: H for hydrogen, O for
oxygen, and Na for sodium. The reactants are
to the left of the arrow
, and the products are
to
the right.
For example, the equation H
2
+O
2
→H
2
O shows that the reactants hydrogen
and oxygen combine to form the product H
2
O, or water.
A.
Look at the reaction shown in the Gizmo.
What are the reactants in this reaction?
Sodium (Na) and Water (H
2
0) are
the reactants
. (Na+H
2
O)
B.
What are the products in this reaction?
NaOH+ H
2
These symbols represent sodium hydroxide and hydrogen gas. Sodium
hydroxide is
a strong base.
(C
hemicals
that contain the hydroxide
ion
(OH
–
) are bases.
)
C.
How do the products of the reaction relate to the
phenol red test and the
splint test?
The products of the reaction relate to these tests based off the fact there are
bases
and acids.
2018
Activity B:
Conservation of
matter
Get the Gizmo ready
:
Click
Reset
.
Select
Hydrogen peroxide
for
Reactant 1
and
Potassium iodide
for
Reactant 2
.
Goal:
How does the mass change
(or not change)
during a chemical reaction?
1.
Review
:
In this reaction, hydrogen peroxide is added to a potassium iodide solution. Click
Play
and observe the reaction.
A.
What do you observe?
As the liquids mix, there is some type of gas released
,
sizzling/fizzing,
and the color
of the liquid
change
s.
B.
What evidence do you see that a chemical reaction is taking place?
There is a change in t
he physical appearance and gas is released
possibly.
C.
Replay the reaction and use the available tools (
Thermometer
,
Phenol red
, and
Glowing splint
.) What do these tools indicate?
(Note: You will need to switch to the
Gas collection
setup to use the splint.)
Thermometer:
Start: 21C & Current: 83C
Phenol red:
Start & End pH: Neutral
Glowing splint:
Glowing splint ignites.
2.
Record
:
Click
Reset
, and change
back
to the
Normal setup
. Notice the mass shown on the
electronic balance.
A.
What is the starting mass for this reaction?
336.6 g
B.
Click
Play
. What is the mass when the reaction has finished?
335.2 g
C.
How does the mass change
in this reaction?
The mass number decreases in this
reaction because the liquid is transformed into a gas a
nd releases into the air
causing the mass to change.
3.
Record
: Click
Reset
, and select the
Gas collection
setup. Notice that this setup is heavier
than the normal setup, but the amounts of reactants is the same.
A.
What is the starting mass for this reaction?
2386.6 g
B.
How do you think the mass will change during the reaction?
I think the mass might
remain the same throughout the reaction.
2018
C.
Click
Play
. What is the mass when the reaction has finished?
2386.6 g
(Activity B continued on next page)
Activity B (continued from previous page)
4.
Explain
:
Why do you think that mass was lost when the reaction was done in the normal
setup, but stayed the same when the reaction was done in the gas collection
setup?
I thi
nk the mass might have stayed the same in the gas collection setup because the
reaction was balanced but in the normal setup it wasn’t and the gas had to be
released.
A fundamental law of chemistry is
conservation of ma
tter
. This law states that, in a
chemical reaction, matter can neither be created nor destroyed. That means that,
as long as
nothing escapes from the system, the total mass measured at the start of the
reaction will be
the same as the total mass at the end of the reaction.
5.
Compare
:
Tur
n on
Show chemical equation
. The small numbers, called
subscripts
, show
how many of each atom there are in the molecule. For example, the molecule H
2
O contains
two hydrogen atoms and one oxygen atom.
(Notice that, in this reaction, the potassium
iodide (KI
) acts as a
catalyst
. A catalyst is a substance that helps a reaction happen but
does not change
during
the reaction.)
Count the total number of hydrogen and oxygen atoms on the left and right sides
of the
equation:
Left side: H
:
2
O
:
2
Right side:
H
:
2
O
:
3
What do you notice?
That there was an additional oxygen atom produced.
6.
Turn on
Show balanced equation
. A balanced equation shows how many molecules of
each substance take part in the reaction. The
coefficients
are the big numbers that tell you
how many molecules there are. For example, “2H
2
O” means there are two water molecules
and a total of four hydrogen and two oxygen atoms.
Carefully count the total number of hydrogen and oxygen atoms on the left and
right
sides of
the balanced equation:
Left side: H
:
4
O
:
4
Right side: H
:
4
O
:
4
A.
What do you notice?
Both sides are balanced out and
equivalent in the equation.
2018
B.
How does the balanced equation relate to the law of conservation of matter?
It
relates because nothing is created nor destroyed from this reaction which is
demonstrated by
the numbers remaining the same before and after the reaction.
Activity C:
Types
of reactions
Get the Gizmo ready
:
Click
Reset
. Select
Normal setup
.
Select
Sodium
for
Reactant 1
and
Chlorine
for
Reactant 2
.
Goal:
Explore, observe, and classify
a variety of chemical reactions
.
1.
Observe
:
In this reaction, a small piece of sodium is
added to a flask co
ntaining poisonous
chlorine gas
which has a yellowish color
, and sand. Water is added to start the reaction.
A.
Click
Play
.
What
happens
?
A flame is ignited and then burn
s out.
B.
Try the experiment with the
Thermometer
. Is the reaction exothermic or
endothermic?
Exothermic; heat is released and the temp rises
C.
Run the experiment one more time, this time watching the mass. What do you
notice?
The mass increases by the end of the reaction.
D.
Repeat the experiment, this time
in the
Closed system
. How does the mass change
during the reaction now?
The mass chang
es during the reaction but concludes as
the same mass as before.
2.
Challenge
:
Turn on
Show chemical equation
.
In this reaction, solid sodium reacts with
chlorine gas to form solid sodium chloride (NaCl), also known as table salt.
How does this explain the
normal setup
increase in mass during the reaction?
When the
new substance is created it explains the
increase in mass because it adds to the original
mass.
3.
Observe
: Select
Ammonium nitrate
for
Reactant 1
and
Water
for
Reactant 2
.
Add the
Thermometer
to the flask and click
Play
.
A.
What
do you observe
?
The temperature decreases by 8.
B.
Is this
process
exothermic or endothermic?
Endothermic
2018
C.
What is the equation for this
process
?
NH
4
NO
3
+H
2
O
NH
4
+
+ NO
3
–
+H
2
O
In this example, ammonium nitrate (NH
4
NO
3
)
dissolves
in water, producing
ammonium (NH
4
+
) and nitrate (NO
3
–
) ions.
Chemists do not all agree
about whether
this
is a
n example of a
physica
l change
or a chemical change.
(Activity C continued on next page)
Activity C (continued from previous page)
4.
Classify
: There are manytypes of chemical reactions. Four are described below:
Synthesis
: Two or more reactants combine to form a single product.
For example,
2H
2
+O
2
→ 2H
2
O.
(Synthesis reactions are also called
combination
reactions.)
Decomposition
: One reactant breaks
down
to form two or more products.
For
example, 2KCl → 2K + Cl
2
.
Single
replacement
:
An element reacts with a compound to form another element
and compound. For example, Zn + 2HC
l
→ ZnCl
2
+H
2
.
Double replacement
: Two compounds react to form two different compounds.
For
example, FeS + 2HCl → FeCl
2
+H
2
S.
Using the Gizmo, find an example of each type of reaction.
Synthesis:
Na +
Cl
2
NaCl
2
Decomposition:
H
2
O
2
H
2
O+O
2
Single replacement:
Na + H
2
O
NaOH + H
2
Double replacement:
AgNO
3
+ HCl
AgCl + HNO
3
5.
Explore
: Find an example of each of the following in the Gizmo:
A.
An example of
no
chemical reaction occurring:
Sodium & Kerosene (N
a+C
12
H
26
Na + C
12
H
26
)
B.
A reaction that produces an acid:
Silver Nitrate
&
Hydrochloric acid
(AgNO
3
+ HCl
AgCl + HNO
3
)
C.
A reaction that produces a base:
Calcium chloride & Sodium hydroxide (CaCl
2
+
2NaOH
Ca(OH)
2
+ 2NaCl)
D.
A reaction that uses a catalyst:
Hydrogen peroxide & Potassium iodide (2H
2
O
2
2H
2
O+O
2;
Catalyst: KI)
2018
6.
Demonstrate learning
:
Choose an interesting reaction in the Gizmo. Use the available tools
to make observations, and use what you have learned so far to draw conclusions
about the
reaction. Describe your findings below.
(If necessary, continue on a secon
d sheet of paper.)
Reaction:
Reactant 1:
Ammonium nitrate & Reactant 2: Potassium hydroxide
Findings:
Results in Normal setup
Data
Before Reaction
After Reaction
Mass
317.2 g
315.1 g
Temperature
21C
31C
Phenol red pH
Basic
Neutral
Smell
Strong
ammonia smell
Strong ammonia smell
In conclusion, it takes multiple elements/substances to form a chemical reaction.
The chemicals
can react by releasing and producing matter effecting the mass. There can even
be heat
involved and makes an endothermic or
exothermic reaction. You may test your chemicals by
monitoring the temperature and pH levels.