My previous tutorial shows how to construct a simple sheet metal “bridge,” which, in combination with an ice cube bucket and an olive jar, makes an effective pneumatic trough for collecting gas samples over water. This tutorial shows how to use this apparatus to generate and collect pure oxygen, and how to use that oxygen to observe the brilliant blue flame of sulfur oxidation. The manganese dioxide catalyst used in this process is easily recovered from a spent zinc-carbon battery.
Projects from Make: Magazine
Collect Oxygen Over Water
Collect pure gas samples with simple equipment.
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Steps
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Step #1: Apply grease to jar rim
- Apply a bead of waterproof grease around the rim of the jar, which I will refer to henceforth as the "column."
- The grease will ensure a tight seal against the plate glass lid once the gas has been collected.
- Although I used petroleum jelly as a sealant, as a general rule, flammable greases like petroleum jelly should not be exposed to pure oxygen. There is no appreciable danger in this experiment, which involves only a small volume of oxygen at atmospheric pressure in a container with a free lid, but if you are working with larger volumes of oxygen, oxygen under higher pressure (as in a cylinder), or (most emphatically) liquid oxygen, do not use grease or other readily oxidizable materials in constructing apparatus.
Conclusion
The oxygen generating-reaction is as follows:
2H2O2 --> 2H2O + O2(g)
The only products are water and oxygen. Manganese dioxide is present as a catalyst, meaning it is neither consumed nor created during the course of the reaction, and is added only to accelerate the decomposition of hydrogen peroxide. That means it can be preserved and reused indefinitely. To recover it, pour the contents of the Erlenmeyer flask, and any washings that contain the black manganese dioxide powder, into an evaporating dish or shallow, wide-mouth jar. Then just set it aside in a window and/or in front of a fan and let the water evaporate away. The dry manganese dioxide that remains can be reused more-or-less indefinitely. If you're impatient, you can filter the manganese dioxide out of the water using a coffee filter to speed the whole process up.
