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Station 1: Dry
Ice Experiments / Producing CO2 in a reaction
1.
WHAT IS DRY ICE
Put
a flat chunk of dry ice on the counter and see how easy it
"floats" on top of the counter when you give it a small push.
Also see how finely ground dry ice moves around on the counter.
Does a puddle of liquid form?
No, Why not?
Solid
--> Gas (
Sublimation)
Put a quarter on the edge of the
dry ice. What do you observe or hear?
What is dry ice? It is
solid, frozen CO2
We breathe in O2
breathe out CO2. Are we going to run out of O2
on earth?
No. Trees and plants take in CO2, produce O2.
Why does it hurt to touch the
dry ice? Have students touch it but only very briefly.
At room temperature and pressure
CO2 wants to be a gas. In solid CO2, the
molecules hold onto to each other. It requires heat to pull
molecules away from each other. The solid takes heat from the
air molecules surrounding it. When you touch dry ice for more
than a few seconds it hurts. It takes the heat from your hand
when you touch it.
2.
CAN WE BLOW UP A
BALLOON WITH SOLID CARBON DIOXIDE?
Students will see how the dry ice goes from a solid to a gas by
putting a chunk of dry ice into a balloon. Stretch a balloon
wide-open using both hands put your fingers deep into the
balloon to stretch it open as wide as you can. Using a pair of
tongs, have a student place a small piece or a couple small
pieces of dry ice in the balloon. Tie the balloon shut and
watch it inflate as the dry ice sublimes (solid --> gas). One of
the students can keep the balloon to be used for the liquid
nitrogen station.
What is the white frost on the
outside of the balloon? Some students think dry ice goes
through the balloon. Discuss water vapor in the air and how it
condenses on the balloon because it is cold. Feel how cold it
is.
3.
MAKING
FOG
Fill a plastic tub with hot
water from sink. Pour one to two cups of ground up dry
ice into the hot water, all at once. What do you observe?What
is the fog? Why does it flow over the edge of the container and
down to the ground?
FOG:
The fog is not just CO2
(g). When you
breathe out CO2, it is clear. The water vapor above
the hot water condenses. As the CO2 sublimes, CO2
(s)
--> CO2
(g), it absorbs
heat, making it very cold so water condenses (like fog or
clouds).
Why does the fog drop to
the floor? It is heavier then the air. Talk about fire
extinguishers which contain CO2
(l) which forms CO2
(g), and drops
down onto the fire, keeps O2
(g) away from
fire, so it extinguishes the fire. Light a birthday candle and
have the students put it in the fog. They will see that the CO2
(g) blows out the flame immediately.
Fill a 250-mL beaker about
half-way with water.
Put a small chunk of dry ice in the water. Students can see
bubbling as the CO2 (s) --> CO2 (g)..
4.
WHAT IS THE DIFFERENCE
BETWEEN ICE AND DRY ICE?
Have students place 40 mL of
water in three 100 mL beakers. Place the beakers on a stir
plate. Students put universal indicator in each beaker stir
the solution with a stirring rod. To one beaker add some ice;
to the other beaker add a chunk of dry ice. What do you see?
The CO2 dissolves
in water to produce carbonic acid, H2CO3:
CO2 + H2O
--> H2CO3 --> H+ + HCO3
making the solution acidic.
Students will see a color change for the dry ice / water
reaction and not for the regular ice dissolving in water. Let
other students try this. Explain what universal indicator is.
5.
WHAT
ARE THE BUBBLES IN SOFT DRINKS?
Talk about CO2
(g) in sodas.
High temperature or high pressure (shaking soda) releases CO2
(g). Gases like
carbon dioxide and oxygen dissolve in water this is good
because aquatic plants, fish and all living species in water
need carbon dioxide and oxygen to survive.
TESTING 7UP IS SODA ACIDIC?
Add 7up to the third beaker
containing 40 mL of water and indicator. What do you see?
7up contains carbonic acid
which reacts with water just like dry ice reacts with water!
The CO2 dissolves in
water to produce carbonic acid, H2CO3.
Carbonated beverages all have CO2 dissolved in
solution.
CO2 + H2O
--> H2CO3 --> H+ + HCO3
making the solution acidic.
So if we add dry ice to a bowl of juice at Halloween, is it safe
to drink?
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