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Simple experiment to measure atmospheric Oxygen

  1. Apr 4, 2013 #1
    I am doing a biology project in which I needed to measure the O2 in the test chamber to determine how much activity I had. The Oxygen sensor I bought on eBay was long expired and useless. O2 instruments were at least $120 used. So I began looking for a simple cheap solution to do it with common items. One method I found was to put a small piece of steel wool (ultra fine 0000) at the base of a test tube, invert it in water, mark the tube, and wait till rusting consumed the oxygen. Then mark the new level and compare the volumes. That could work for me, but it takes several days to get a reading. I was hoping for something faster. I thought about the getters in vacuum tubes and wondered how those worked. Basically they use thin films of active metals and heat them with electromagnetic radiation to ignite the material. Well I have a microwave in my kitchen. An idea began to form.
    1) I got a small graduated cylinder. I used a 10 ml cylinder. $5 ebay
    2) some steel wool, very fine, and I found stretching it out into a yarn like spiral works best.
    3) a bent soda straw
    4) a microwavable glass container. A beaker would be perfect.
    5) a kitchen microwave.
    You take the steel wool and slide it to the bottom of the cylinder, leaving the spiral to run an inch down the tube. The fuzzier the wool sample the better it works. You fill the glass container with cold water. Place the short end of bent straw into the cylinder and invert it into the water. This next part is tricky. You need to suck air out through the straw till the water rises to the 10 ml mark (or the level you are using). You have to do this while the level of the water outside the cylinder is the same level as the water at your mark is. Otherwise the differential pressure will effect your reading. Also it's a very good idea to pour cold tap water over the cylinder into the container before you do this. This will give you a base temperature setting. Place the container with the inverted tube in the microwave. REMEMBER keep your sample of steel wool small. I used what would have been about the volume of three Que Tips stretched out. You want it to get hot and burn without shorting out your microwave. I found a series of three or four ten second shots were sufficient. Amazingly it doesn't leave burn marks in the tube. It will flash white and them burn orange for a moment. I think each shot lets more of the oxygen get up to the iron. Then take it out of the microwave and run tap water over the cylinder till the warm water in the container has all washed out and the cylinder and entrained air are at the original temperature. Now raise the cylinder till the inside and outside levels of water are the same and take your reading. I got 1.9 ml less or 19% oxygen. Clearly there is still a little O2 left to burn, and the volume of the steel wool reduces the volume of air, but within 10% isn't bad for a cheap experiment.
    I am waiting on some nice Chinese all glass 100 ml syringes I bought on eBay for $10. This will allow me to suck samples from my test chamber, pinch the plastic sample tube with a non-conductive item, and do the whole experiment horizontally. I may not even need water, the piston in the syringe may pull down 21%.
     
  2. jcsd
  3. Apr 5, 2013 #2

    Borek

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    Staff: Mentor

    Drawing wouldn't hurt, just like splitting the text into paragraphs.

    I have a feeling you are reinventing the wheel. There are good and cheap volumetric (titration) methods of determining the amount of oxygen (like Winkler method), and they will give you much better accuracy. You may have to modify the procedure as you are not dealing with the dissolved oxygen alone.
     
    Last edited: Apr 5, 2013
  4. Apr 5, 2013 #3
    I'll check it out, though I'm not looking at dissolved oxygen levels in liquids. Everyone always complains about my paragraph lengths. I've never been able to get my arms around what I'm doing wrong. Maybe my wife can coach me. Thanks for the feedback.
     
  5. Apr 5, 2013 #4

    Borek

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    Staff: Mentor

    Yes, that's why I mentioned you may have to modify the method. I believe it should be possible to reuse the chemistry, just modifying the procedure, to measure amount of oxygen present in the sample.
     
  6. Apr 19, 2013 #5

    NascentOxygen

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    Staff: Mentor

    If you first pickle the steel wool in acid you'll give it an etched and unoxidized surface (reactive and many times the area it originally had), and you may find the reaction with oxygen proceeds almost as you watch, possibly within minutes. I can't comment on whether this may affect accuracy.
     
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