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Mmol to mg/l

  1. Jul 8, 2014 #1

    Sorry to post here with what I believe will be a relatively simple response.

    I am not a scientist but a fish keeper and would like to know how to convert 2 mmol of nitrite in to mg/l and subsequently ppm which I believe is equal to mg/l

    The molecular mass of nitrite is 46.01.

    I tried to google this but the explanation was not clear cut enough for me to get m head around and work out for myself.

  2. jcsd
  3. Jul 8, 2014 #2


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    Staff: Mentor

    I take it to mean 2 mmol of nitrite per 1 lire?

    If mass of one mole is 46.01 g, what is the mass of 2 millimoles?
  4. Jul 8, 2014 #3

    Yes. Is it that simple. I did think as much. I wanted to use this to argue my claims. Nitrite is toxic to fish. But a paper on the toxicity of nitrite to the zebra fish were using 2mmol before nitrites began harming and killing 50% of the stock. It did not say mmol/l. It read mmol-1 (-1 being super scripted)

    Does this mean that 2mmol/l is 92.02 mg/l? That would be 92.02 ppm right.

    In fish keeping people state that you should immediately replace at least 50% water when test results show >1ppm

    From what I have learned about nitrites I don't believe this is at all necessary.
  5. Jul 8, 2014 #4


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    Staff: Mentor


    mmol-1 means just [itex]\frac 1 {mmol}[/itex] - but it is not concentration. mmoll-1 (note two l's) would mean [itex]\frac {mmol} l[/itex] (and this is concentration).


    Hard to say - no idea how the LD50 was found (how long they waited). Could be lower concentrations are toxic as well, it just takes longer. Or fish don't die, but they are not able to reproduce.
  6. Jul 8, 2014 #5

    They were talking in LC50 not LD50 or LDt50 although time was a factor. Apparently fish have reductase cells that begin to combat the formation of methemoglobin in blood cells so I think once a balance is achieved between formation and reduction this would leave a percentage of methemoglobin in the cell. This percentage may not necessarily be detrimental to the fish.

    I'm not saying nitrites should not be taken seriously. I just think some people over react. This works in favour of companies like Seachem that create a product called prime that detoxifies nitrites. A bit of scaremongering and they fly off the shelves.

    Maybe you could interpret the article better than me?

  7. Jul 8, 2014 #6
    Or the abstract in this article if you can spare the time. This one is over 96 how's but the units mg-1 SUP IMP -1 don't mean anything to me. I can't convert that as an expression that I can relate to such as ppm if at all possible.
  8. Jul 8, 2014 #7


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    Staff: Mentor

    No idea what you are talking about. Abstract refers to concentrations given as mmol l-1, which - as I already told you - means [itex]\frac {mmol} l[/itex].
  9. Jul 8, 2014 #8

    What is [/itex]?
  10. Jul 8, 2014 #9


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    Staff: Mentor

  11. Jul 8, 2014 #10

    I don't think it is rendering. Even the link provided still shows itex etc.

    Never mind. Is there anyway you can tell me what me what 242 mg•1 to the minus 1 is in parts per million or are you saying that this value is not a concentration but rather a quantity?

    Sorry if you have already told me. It just isn't making sense.
  12. Jul 8, 2014 #11


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    Staff: Mentor

    Concentration is the amount of the substance per the amount of the mixture. The way of expressing the amount of the substance and the way of expressing the amount of the mixture just changes units, but not the general idea that concentration must be a ratio.

    mmol*l-1 is just another way of stating mmol/l (note: it is small l as in liter, not 1). a-1 means 1/a, that's how raising to power works.

    So if you want any of the numbers listed to mean concentration, it must be a ratio. 242 mg/l (and not 242 mg*1-1) means 242 mg in 1 liter of solution. As mass of 1 liter of water is close to 1 kg it will typically mean 242 mg per 1 kg, or 242 parts per million - ppm (here it is 242 mg - amount of substance - per 1 million of mg of the mixture, so it follows the idea of the concentration being expressed as a ratio).
  13. Jul 8, 2014 #12

    Thank you this makes much more sense. So it looks like I was confusing lower case L with a 1 as they look so similar!
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