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Question regarding concentration units

  1. Jul 25, 2016 #1
    Hi all,

    I've done some experiments and I'm trying to work out the correct unit of my final concentration. The experiment goes thus far:
    I added 800 uL of a substance into a litre of my sample (800uL/L).
    This substance has a density of 1020 kg/m3 and is 60% w/w.
    I'm trying to work out the amount of substance per litre of sample.
    After my calculations I have arrived at a number of 490 but I will appreciate some clarification on this as well as if the correct final unit of concentration will be ug/L or mg/L.

    Thanks in advance.
     
  2. jcsd
  3. Jul 25, 2016 #2
    800 ##\mu L## = 0.8 cc

    1020 kg/m3 = 1.02 gm/cc

    (0.8)(0.6)(1.02) = 0.49 gm = 490 mg
     
  4. Jul 25, 2016 #3
    Thanks a lot for your reply, truly appreciated.

    I have one more question, what if the density was 1.020 kg/m3?

    Will the final concentration still be in mg/L or ug/L?
     
  5. Jul 25, 2016 #4

    mfb

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    2016 Award

    Staff: Mentor

    I moved the thread to our homework section.

    As long as you keep your units consistent, that problem never comes up.

    1.020 kg / m3 * 1m3/(1000 L) * 800 µL * 0.6 = ..
     
  6. Jul 25, 2016 #5
    That's a pretty low density
     
  7. Jul 25, 2016 #6
    Yes, but that's what is quoted on the data sheet for the substance.

    This is the calculation I did:

    Mass = D x V = 1.02mg / mL x 0.8mL / 1000 mL = 0.000816 mg/mL = 0.816 mg/L = 816 ug/L
    816 ug/L x 60% = 490 ug/L
     
  8. Jul 25, 2016 #7
    So, where did the 1020 kg/m3 come from? This is 1.02 gm/cc.
     
  9. Jul 26, 2016 #8

    mfb

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    2016 Award

    Staff: Mentor

    1.020 kg/m3 is a density lower than air. There is no liquid with that density.

    Could the source be from some foreign country? Compared to English, some other languages have a swapped use of "," and "." for numbers (e.g. 12345.6 can be written as 12.345,6), so 1.020 could mean 1020.
     
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