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Thread: Hi, need some help with bizarre dissolved oxygen levels

  1. #1 Hi, need some help with bizarre dissolved oxygen levels 
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    My class is building ecocolumns and our Dissolved oxygen tests are coming back at 10+ppm (today most were 20+). Many had low DO levels in the beginning but it seems that everyone has a high DO level. Current factors are
    A. Its been raining
    B. They are somewhat close together (There is about 15-20)
    C. Its been cold

    I think it could be a problem with the DO tests we are doing (Its a standard take sample of water, add Chem A, shake, Chem B, shake and wait, Chem C, shake, Chem D and add one drop and shake (each drop is 1 ppm).

    Any help would be greatly appreciated.


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  3. #2  
    Moderator Moderator AlexP's Avatar
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    I take it these ecocolumns (I don't know what they are exactly) are outside? Going from what I know about dissolved oxygen, I think the rain and the cold temperatures would actually increase dissolved oxygen levels. Being pelted by rain I would think would aerate the water, and cold temperatures help gases to dissolve more easily in liquids. I don't think it would be a problem in the test unless you're not following the directions correctly...


    "There is a kind of lazy pleasure in useless and out-of-the-way erudition." -Jorge Luis Borges
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  4. #3 Hi need some help 
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    Ok, well the ecocolumns are outside and exposed to the rain. The DO levels are so abnormal that it makes me think something unnatural must be causing this. about 40% of my class has +20 ppms for the DO tests. Any other suggestions?
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  5. #4  
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    You could try checking your reagents.

    You ought to be able to remove most of the oxygen from a water sample by autoclaving the water. Do you have access to an autoclave? A pressure cooker would work, as well.

    Otherwise, what values do you expect? Atmospheric O2 is around 20%, so I don't understand why 20 ppm would be considered high. ?
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  6. #5  
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    Well 20 ppm is quite a bit for a water concentration, http://www.k12science.org/curriculum...turation.shtml
    Most water has around 10 ppm oxygen. Well this is mostly an observation experiment so we are not really trying to remove the oxygen but rather see how it unfolds. I suppose it couldn't help to try a pressure cooker to at least test if our DO level procedure is accurate.
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  7. #6  
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    Ah - I see. I did not realise that DO in water was expected to be so low.
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