Activity #4: Physical vs. Chemical Changes
I can use laboratory observations to be able to determine
the differences between physical and chemical changes.
Background: Chemical substances are always coming in contact with other
chemical substances in the natural world. These substances are also exposed to the
physical variables of the environment, like temperature changes and applied forces.
This combination, in turn, influences the stability of these chemical substances and
may or may not change their physical state or the chemical makeup of the
substances altogether. In part A of this activity, you will observe how variables in
the physical environment change chemical substances. Then, in part B, you will
observe how chemical substances change in the presence of other substances. By
the end of the activity, you will be able to identify what evidence would lead a
chemist to determine if a physical or chemical change has occurred.
Part A: Physical Changes
1. Obtain an ice cube and place it into an evaporating dish. Place the evaporating
dish onto a hotplate set on high temperature. Observe how the ice cube
changes until the substance seems to “disappear.” Allow the evaporating dish
to cool on a wire gauze.
2. Take a sheet of white paper. Crease the paper lengthwise and rip in two.
Repeat this process over and over until you can no longer rip the paper. Make
sure you get the resulting pieces of paper into the recycle bin.
3. Obtain an antacid tablet. Using a mortar and pestle, grind the antacid tablet
into a powder. Your teacher will demonstrate how to properly use a mortar
and pestle. Save the powder for Part B of the activity.
4. Fill your 150-mL beaker with 60 mL of distilled water. Add a pea-sized
amount of salt to the beaker and stir until dissolved. Pour 30-mL of the salt
solution into your evaporating dish and heat until dryness on a hotplate set to
high temperature. Allow the evaporating dish to cool on a wire gauze.
5. Fill a 150-mL beaker with 60 mL of distilled water. Add one drop of green
food dye. Stir until completely dissolved. Save the solution for Part B of the
activity.
Part B: Chemical Changes
1. Obtain a piece of aluminum wire and place it into the bottom of a test tube.
Add copper (II) sulfate solution to the test tube to a height of one-third the
height of the tube. Let the test tube sit undisturbed while the other steps of Part
B are performed before observing. Till wire is not visible?
2. Light the Tirrell burner and adjust the burner to produce an appropriate nonluminous flame like was learned earlier in the semester. Obtain a strip of
magnesium. While holding the magnesium with crucible tongs, hold the strip
of magnesium at the tip of the inner core of the flame. Tap the product onto a
watch glass to observe.
Note: DO NOT LOOK DIRECTLY INTO THE BURNING MAGNESIUM.
3. Transfer the ground antacid tablet to a 150-mL beaker. Carefully add 50-mL
of hydrochloric acid. Lower a lighted wood splint into the beaker as the
changes take place. DO NOT DROP THE WOOD SPLINT INTO THE
BEAKER!
4. Add 10 drops of bleach to the mixed green food dye from Part A while stirring.
Add a few drops, if necessary, to get a definite change of the solution. Then
add 10 drops of vinegar while stirring. Add a few more drops, if necessary, to
get a definite change of the solution.
5. Teacher demo: A piece of zinc is placed in 6 M HCl, then the gas is tested with
a wood splint.
Data Table for the Observations of Physical and Chemical Changes
Chemical
Substances and
Change
ice heated
Observations
Before Change
Chunks of solid
intact, white, and
cold
Long and nice
paper torn
width, blank with
sharp edges
antacid tablet Solid, intact,
circle and white
pulverized
sodium chloride White powder
dissolved and
evaporated
food coloring
mixed in water
aluminum wire
in copper (II)
sulfate
Green liquid, and
a separate clear
liquid
Grey rod in blue
liquid
combusted
magnesium
Solid, rigid grey
strip
antacid powder
in HCl
Brown strip
skinny, top had
heat source
Grey chunks
zinc metal in
HCl
Observations
During/After
Change
No longer a solid
but a liquid and is
bubbling, and hot
Short width but
still long, and
sides are rigid
Powder, white,
and not intact
The salt took a
while to dissolve,
it dissolved when
I stirred it
Green liquid
turned clear
liquid green
Liquid turned
clear, but grey
rod turned puffy
and red
The Strip
produced a very
bright light
turned white,
Parts fell off
The mixture
extinguished the
heat source
Bubbles formed;
the liquid got
foggy. When
Can the original
substance be
restored?
yes
yes
yes
yes
yes
no
No
No
No
food coloring
water, bleach,
and then
vinegar
Green liquid
exposed to heat,
the resulting gas
created a
combustion
The bleach turned No
liquid blue, while
the vinegar
turned liquid
yellow
Post-Activity Questions:
1. For which type of change could you restore the original chemical substance
after the change?
Physical change
2. Place the following changes into the appropriate column
Evidence of a Physical Change
explosion
grind/pulverize
cut/tear/saw
change of color
melt
Dissolve
gas production
Evidence of a Chemical Change
signs of new matter
explosion
production of heat
formation of light
evaporating
boil
3. Were there any changes that fit into both categories? If so, what would you
have to do to ensure that a specific type of change occurred?
Yes, change of color, gas production, production of heat, formation of light and
explosion are all dual-category. You’d either have to cool or heat it or mix it
with a specific metal. If you can undo the interaction, then you’ve made a
physical change. If you can’t, or new matter was formed, then you’ve made a
chemical change.
4. Did the water heated in the evaporating dish in Part A really disappear? If not,
explain what happened.
No, the heated water evaporated and turned into a gas.
5. What do you believe was the white residue left in the evaporating dish after
heating the salt solution?
The salt.
6. Explain how the gas produced from the reaction of antacid and HCl differed
from that of the gas produced from the reaction of zinc metal and HCl. What
do you believe the two gases were?
Zinc and HC1 produced hydrogen gas, while antacid and HC1 formed Co2.
Hydrogen gas was flammable, while co2 put out the fire.
7. Watch the following two videos.
https://www.youtube.com/watch?v=0Ad9tholMEM
https://www.youtube.com/results?search_query=hindenburg
Explain how the observations of zinc and hydrochloric acid relate to this
tragedy.
Zinc and hydrochloric acid produce hydrogen gas, which is flammable and what
Hindenburg was filled with. A spark ignited the gas and caused the tragedy.
8. Write the chemical formula for the following chemical substances used in this
activity.
antacid (calcium carbonate) NaHCO3
sodium chloride NaCl
copper (II) sulfate CuSO4
bleach (sodium hypochlorite) NaClO
vinegar (acetic acid) CH₃COOH