Download Determination of the Molar Volume of a Gas KClO3 breaks down

Determination of the Molar Volume of a Gas
KClO3 breaks down upon heating to produce KCl and O2. Addition of a small amount of MnO2 as
reaction catalyst makes the reaction go more smoothly. Because molecular oxygen is the only volatile product
of this reaction, the loss of mass of a tube containing potassium chlorate upon heating indicates the mass of the
molecular oxygen produced. The number of moles of oxygen liberated can be calculated from the number of
grams of oxygen produced using the molar mass of the molecular oxygen. If the molecular oxygen generated
from the reaction is passed into a flask filled with water, the oxygen gas will displace water from the flask. The
volume of water displaced will be equivalent to the volume of the oxygen gas produced. After a short cooling
period, the gas may be assumed to be at room temperature. The pressure of the molecular oxygen will be equal
to the atmospheric pressure minus the vapor pressure of the water that is also trapped in the flask with the
oxygen at room temperature.
Procedure:
1.
Obtain a set of tubing, stoppers and a clamp that have already been prepared from the laboratory
instructor. Fill a 500 mL flask to about 2 inches from the top with water and assemble as shown in the
figure below. Use a 600 mL beaker and a dry, pyrex test tube.
2.
3.
4.
5.
6.
7.
Open the pinch clamp on the rubber tubing and blow into the short tube until water drains into the
beaker. Then, close the clamp.
Transfer about 3.5 grams of the potassium chlorate - manganese dioxide mixture to the test tube.
Determine the mass of the test tube and contents.
Attach the test tube to the set-up as indicated in the drawing and spread the contents over the bottom 2
inches of the tube. Open the clamp. A few drops of water may drain from the tube into the beaker, but
the flow should stop quickly. If water continues to drain, there is a leak in the system and the apparatus
should be taken apart and reassembled. Empty the beaker after it is clear there are no leaks in the
system.
Warm the contents of the test tube gently using a small burner flame. It is important that the oxygen not
be generated rapidly in order to avoid popping out any of the stoppers. Start heating the contents on the
end of the tube closest to the flask and try to keep the rate of oxygen production fairly constant.
Stop heating when the water level in the flask is about 2 inches above the end of the long tube. Allow
the entire system to cool to room temperature with the clamp on the open and the outlet under the
surface of the water in the beaker.
Close the clamp after the apparatus has cooled to room temperature. Measure the volume of the water in
the beaker by transferring it to a 500 mL graduated cylinder.
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Principles of Chemistry 1
8.
9.
10.
Molar Volume of a Gas
Disconnect the test tube from the apparatus and determine the mass of the test tube and contents.
Record the temperature and the barometric pressure.
Refill the flask with water and reattach the test tube to the apparatus. Repeat the heating process and
collect and measure a second sample of molecular oxygen
DATA
Mass of empty tube (g)
_____________________
Mass of test tube and mixture before heating (g)
_____________________
First Heating
Mass of test tube and mixture after first heating (g)
_____________________
Volume of water displaced during first heating (mL)
_____________________
Barometric pressure (mm Hg)
_____________________
Temperature
_____________________
Vapor pressure of water at this temperature
_____________________
Second Heating
Mass of test tube and mixture after second heating (g)
_____________________
Volume of water displaced during second heating (mL)
_____________________
Barometric pressure (mm Hg)
_____________________
Temperature
_____________________
Vapor pressure of water at this temperature
_____________________
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Principles of Chemistry 1
Molar Volume of a Gas
CALCULATIONS
1.
Calculate the mass of molecular oxygen evolved during each heating (trial).
Trial 1:
Trial 2:
2.
Calculate the number of moles of molecular oxygen evolved during each heating (trial).
Trial 1:
Trial 2:
3.
Calculate the partial pressure of the oxygen in the flask using the atmospheric pressure and the water
vapor pressure.
Trial 1:
Trial 2:
4.
Calculate the volume of one mole of oxygen under laboratory conditions using a ratio including the
volume and number of moles each oxygen sample.
Trial 1:
Trial 2:
5.
Adjust the volume of one mole of oxygen under laboratory conditions to standard temperature and
pressure (STP) conditions. Be sure to take significant figures into account!
Trial 1:
Trial 2:
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Principles of Chemistry 1
6.
Molar Volume of a Gas
Average the results obtained in question 5. to obtain a "final" value for the molar volume of a gas.
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