LAB: Carbon Dioxide Properties
Students taking Scholars Online AP Chemistry in the fall should consult with the instructor for additional AP lab instructions to use for this experiment.
Goal: To demonstrate that carbon dioxide gas is heavier than air.
If you cannot get calcium hydroxide, you can skip the final step of this experiment.
- Baking soda
- Deep jar
- Two small candles (such as birthday cake candles)
- Scale or equal arm beaker (part II)
- Calcium hydroxide (part III)
- Erlenmeyer flask and stopper (part III)
- Distilled water (part III)
- Two jars, or one beaker and one flask
- A lid for one of the jars, or a two-hole stopper for the flask
- Straws or glass or plastic tubing
- Useful: a very small funnel; if necessary, you can roll some foil to
- Short length of flexible tubing (rubber, clear plastic, available at
Procedure: Gas collection phase
- Set up the gas collection apparatus to resemble the picture on p. 121
of the Lectures.
- If you use jars, you can create a seal with the lid for the jar this
- punch two holes in the lid, and force a straw through each hole
- put some modeling clay around each straw above and below the jar to
seal the opening in the jar
- If you use the two-hole stopper, carefully push the short glass or
plastic tubes through the stopper openings. You may want to wrap the tubes
with a cloth as you push to minimize the chance of accidents.
- One of the straws or tubes should be long enough to reach almost to
the bottom of the jar or flask. The second tube should be short, just long
enough to stick completely through the lid or stopper into the jar and
(if using clay) the clay seal.
- Attach the flexible tubing to the shorter of the straws or tubes coming
out of the jar, and place the other end of the tube in the second jar or
in the beaker.
- Put several table spoons of baking soda in the bottom of the jar or
- Seal the jar or flask
- Using the funnel, pour about 1/4 cup of vinegar (any kind will do,
but white is cheaper) down the open-ended tube into the sealed jar. Add
enough so that the level of the liquid reaches the bottom of the long tube
and prevents any gas produced by the reaction from escaping up that tube.
The carbon dioxide gas produced by the reaction of vinegar and baking sode
will then expand and move up the second tube, through the flexible tubing,
and into the jar.
- When your reaction stops, cover your carbon dioxide collection jar
with a lid or a piece of cardboard.
- If you can't do the collection method above, mix a small amount of baking soda and vinegar in a jar. Allow the reaction to run until it stops.
- Using an eyedropper, remove as much of the remaining liquid from the bottom of the jar as possible. Keep the jar level and work on one side, so as to disturb the gas in the jar as little as possible.
Note: In the following tests, you may need to generate more carbon dioxide.
Procedure: Gas combustion properties
- In your large jar, tape one of the small candles as close to the bottom
of the jar as possible. Leave the wick area clear.
- Tape the second candle so that it lies completely in the jar, with
the wick just below the rim.
- Light the both candles and let them burn for a few seconds to make
sure that they will burn easily.
- Pour your carbon dioxide into the jar and make a note of your results.
[If you used plan B, DO NOT POUR any remaining liquid mixture into the large
jar; the idea is to pour the gas above it as though the gas were some lighter
liquid floating on the vinegar solution.]
- See if you can put the shorter candle out without extinguishing the taller candle.
- Does carbon dioxide burn?
Procedure: Gas weight
- Weigh a small empty beaker and make a note of its mass.
- Pour carbon dioxide gas from your collection vessel into the empty beaker. See if you can figure out a way to determine whether your beaker is full of carbon dioxide.
- How does the mass change?
- What volume of carbon dioxide have you collected?
- Can you determine the density of the carbon dioxide from your mass and volume measurements?
Procedure: Gas identification test
- Mix 2 gm of calcium hydroxide in 1 liter of distilled water (this is enough to create a saturated solution).
- Allow the solution to sit overnight.
- Pour off the solution carefully; do not disturb any undissolved calcium hydroxide at the bottom. If possible, use filter paper (coffee filters will work) to obtain a clear CaOH solution. This is limewater.
- Pour a small amount (25-50mL or so) in a flask.
- Pour some of your carbon dioxide gas into the flask and stopper it.
- Shake the flask and observe any reaction that occurs.
Okay, so this time you have no measurements to make. You need to work
on the explanation of your procedure and the description of observations.
- Be sure to accurately describe your apparatus.
- Consider how you might create a control to show that the candles are
changing behavior because of the presence of carbon dioxide and not for
some other reason.
- How could you test the gas produced by the vinegar reaction in other
ways to determine its composition. How could you know that it isn't oxygen
or hydrogen, for example?
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