Molar Volume of Oxygen. The Experiment.

Molar Volume of Oxygen
Generating and Collecting O₂

This is a quantitative experiment.
The Analytical Balance will allow you to measure to 3-4 sig figs...
A. the mass of UNKNOWN used
B. the mass of Oxygen generated
The amount of UNKNOWN you will be using will be between 200-300 mg.
2 KClO3 ------> 2 KCl + 3 O₂
From the above equation you can determine the amount of oxygen you will genertate will be less than125 mg.

For the MOLAR VOLUME portion of this experiment, you must collect and measure the volume of the oxygen generated.
Therefore the connections between the reaction tube and the erlenmeyer flask collecting the gas must be leak proof.

Before assembly, make sure the rubber tubing and rubber stoppers are in good shape without cracks.
In assembling the apparatus, make sure the stoppers are put in gas tight. Pushing them in with a slight twisting motion helps to seal them.
Since the reaction tube will be heated fairly hot, do not use a clamp with rubber or plastic covering to hold it.
The water in the water bath should be at or near room temperature. Before starting, the inverted Erlenmeyer flask should be filled with water and contain no air bubbles.
The 250 ml suction flask is used as a trap. It prevents water, which may accidently suction or siphon back while the heated tube is cooling, from entering the reaction tube.

Two factors affect the gas volume in the system during heating.
1. Oxygen is generated by the decomposition of the KClO₃ (with MnO₂ as catalyst).
2. The air in the reactor is heated and expands.
This increased volume of gas, bubbles out of the system and is collected in the 125 mL Erlenmeyer Flask, displacing the water.
After no more gas bubbles out, shut off the burner and.....
1. Make sure the gas delivery tube in the erlenmeyer flask is in the gas pocket, not the water!
2. Let the reaction system cool to room temperature undisturbed.

At this point think of what you are doing and think about the following questions....
A. What would be the possible effect on this experiment of using more than 300 mg of UNKNOWN? (Clue: you are using a 125 mL flask to collect the gas generated.)
B. If you generate exactly 130 mL of Oxygen in this experiment and the erlenmeyer flask will hold 130.5 mL of gas, your experiment will be ruined. Why?
C. Based on the way this experiment is set up, would you expect oxygen to be very soluble in water?
D. What happens to the gas in the erlenmeyer flask when the reaction tube cools back to room temperature?
E. Why do you put the trap in the system?(Clue: What would happen during cooling if after gas generation the gas delivery tube in the erlenmeyer flask was not in the gas pocket but in the water.)