CHEMISTRY IN CONTEXT
LAB 15: MAD SCIENTISTS LAB, PAGE 1
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MAD SCIENTISTS LAB
Sublimation of Dry Ice & the Law of Conservation of Mass
INTRODUCTION/PRE-LAB DISCUSSION:
When a liquid changes
to a gas, it undergoes
boiling or evaporation. When it comes BACK to
a liquid from a gas, it condenses. When a solid
changes to a liquid, it is melting and when it
goes BACK to a solid, it freezes. The changes
in the state of matter are also types of physical
changes, where a change occurs but the chemical
composition of the compounds does NOT change.
We have spent MOST of the Chemistry in
Context class discussing chemical changes, where
the physical composition of the compounds
involved actually changes. Physical changes must ALSO obey the Law of Conservation of Mass just like chemical
reactions. So, after an object melts, it MUST weigh the same as it did BEFORE it melted when it was solid.
Some substances are odd and mysterious, like the strange mist that enveloped a small town in Oregon and did
untold SCARY damage to it's inhabitants in the movie, The Fog. Dry ice is one such substance. It DOES NOT
MELT! It goes STRAIGHT from solid to gas! But, it still requires a GREAT DEAL of energy to make this
change, and carbon dioxide (the substance of which dry ice is made) will absorb this energy from its
CHEMISTRY IN CONTEXT
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LAB 15: MAD SCIENTISTS LAB, PAGE 2
CYCLE 7
environment, much like the 10,000 Volt Ghost would suck energy from his surroundings in the Scooby Doo
Mysteries.
There is much in the world that is creepy, eery, and misunderstood and
it is up to SCIENCE to explain it... Ask your instructor to show you
the video of a GHOST captured in video footage of a car commercial...
Can you explain the phenomenon? It is up to science to explain OUR
WORLD!
APPARATUS/MATERIALS:
1 small piece of dry ice
1 150mL beaker
1 thermometer
1 pair of beaker tongs (for safety in transporting)
hot water
1 small paper cup
PROCEDURE:
1) Measure the mass of your empty beaker.
2) Fill your beaker with 75mL of hot water from the sink. Add one drop of the dye of your choice to the
beaker of water.
3) Measure the mass of the beaker and hot water. Record this number.
4) Measure the mass of the empty paper cup and record the value.
5) Acquire a small sample of dry ice from your instructor and have him place it in the paper cup. (NOTE:
Hold the cup by the upper edges. Dry ice is VERY COLD and can burn you in the same way a hot
stove would by SUCKING the heat energy out of your skin! So, NEVER touch the dry ice.)
6) Measure the mass of the cup with the dry ice inside.
7) Place your thermometer in the water and measure the temperature. Record the value.
8) Return to your lab stations and carefully and SLOWLY pour the dry ice into the beaker with the glow
stick and water. Observe what happens.
9) Leave the thermometer in the beaker and observe the change in temperature. Record the final
temperature value when all of the dry ice has sublimed.
10) When the reaction has finished, remeasure the mass of the beaker and water. Record your data.
11) Pour the water into the sink for disposal.
CHEMISTRY IN CONTEXT
LAB 15: MAD SCIENTISTS LAB, PAGE 3
CYCLE 7
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DATA/OBSERVATIONS:
A)
Initial Mass of the beaker, water, and dye:
g
B)
Mass of the plastic cup:
g
C)
Mass of the Dry Ice + Plastic Cup:
g
D)
Mass of the Dry Ice:
(found by subtraction of previous two values)
g
E)
Initial Temperature of Water:
o
C
F)
Final Temperature of Water:
o
C
G)
Final Mass of the beaker, water, and dye:
g
ANALYSIS:
1) What is the role of science in our world?
2) Did you increase the mass of your beaker, water, and glow stick by adding the dry ice? (i.e. did your
value for G in the Data/Observations increase by the number in D in the Data/Observations)
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3) If your answer to #2 was NO, where did the mass go? The Law of Conservation of Mass MUST be
obeyed. (HINT: Think about what you SAW during the reaction.)
4) How did the temperature of the water change? Where did this energy go? What type of reaction can
experience significant changes in energy levels?