The Molecular Weight Of Carbon Dioxide Worksheet Page 3
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4Chemistry 11
Santa Monica College
Procedure
Safety
6 M hydrochloric acid is capable of causing serious chemical burns and blindness and should
be handled with care. If the acid comes in contact with your skin immediately rinse the affected
area with water for several minutes. As always, you should be wearing your safety goggles.
Materials and Equipment
The following items must be obtained from the stockroom.
•
A straight piece of glass tubing connected to a piece of rubber tubing
•
A two holed rubber stopper with a thistle tube inserted into one hole and a piece of bent
glass tubing (connected to a piece of rubber tubing) inserted into the other hole
•
A CaCl
drying tube
2
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A piece of aluminum foil that is approximately 15 cm by 15 cm and two 250-mL
Erlenmeyer flasks are also needed. Make sure that the rubber stoppers will fit
tightly into the mouth of each Erlenmeyer flask.
1.
Obtain one of the 250 mL Erlenmeyer flasks. This will be designated as flask B. Make
sure that the flask is both clean and dry. Record the mass of the flask and the foil to the
nearest 0.001 g using the analytical balance. Note that it is mass
that is
(flask + foil + air)
being measured here. Also record the temperature of the air in the flask.
2.
Place about 25 grams of calcium carbonate into the other 250 mL Erlenmeyer flask
designated as flask A. Add about 10 mL of water, or enough to cover the chips
completely. Insert the two-holed rubber stopper (with the thistle tube and the bent tube)
into flask A, making sure that the thistle tube is adjusted so that it is beneath the water
but not touching the bottom of flask. The stopper must fit tightly into the flask. Also obtain
about 25 mL of dilute (6 M) hydrochloric acid, HCl, in a small, labeled beaker.
3.
Assemble the apparatus shown in the figure on Page 4. Insert the straight glass tube
(the one that is attached to the flexible tubing but not attached to the one-holed rubber
stopper) into flask B by placing it between the foil and the flask and pressing the foil
against it to hold it in place. Be careful to fold and shape the foil only as much as
necessary since it is fragile and will easily tear. Attach the flexible end of the tubing to
the drying tube. The small rubber stopper attached to the bent glass tubing should be
inserted into the other end of the drying tube.
4.
When all is ready pour 5–10 mL of the hydrochloric acid into the top of the thistle tube
and allow it to run through the tube and into flask A. The reaction should begin
immediately as evidenced by gas evolution. Allow the reaction to continue for at least 20
minutes to displace all of the air in flask B with carbon dioxide gas. During this time pay
attention to what is happening in flask A; if the gas evolution ceases, add additional HCl
solution through the thistle tube. After the 20 minutes remove the tube from flask B
(keep the foil in place) and immediately weigh the flask containing carbon dioxide on
the analytical balance to the nearest 0.001 g.
Molecular Weight of a Gas
Page 3 of 4
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