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Magnetic Susceptibility of a Solution

  1. Sep 18, 2012 #1
    Hi! I'm trying to calculated the magnetic susceptibility of a solution. I am using this table to know what the susceptibility of each substance is.

    In other words, I want to know how the magnetic susceptibilities of two (or more) substances add up once they are mixed together into a solution. I am not sure how this works, whether it is a simple weighted sum depending on the concentration of each individual substance, or whether it is (as I suspect) much more complex than that.

    Thank you for your help and your time!!
    Last edited: Sep 18, 2012
  2. jcsd
  3. Sep 18, 2012 #2
    I have no experience with that procedure, but here's a 'common sense' opinion, given the generally feeble magnetic properties expected of solutions of diamagnetic/paramagnetic chemicals. On the assumption there are no strong chemical reactions in solution, it should be just a weighted sum - due allowance being made for any demagnetizing factor present in the sample container geometry: see e.g. http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0CD0QFjAD&url=http%3A%2F%2Fwww.ee.ucla.edu%2F~jjudy%2Fclasses%2Fmagnetics%2FEE289-1_Magnetism_Lecture_01p1.pdf&ei=KotYUNrtD6auiQfHvoHoAw&usg=AFQjCNGr3oJ-K1FBtn4R-0dOJQ9detukzw&cad=rja (from around last quarter of article). For diamagnetic or paramagnetic solutions the demagnetizing field should typically be a very small perturbation to the applied field, but it depends on how accuate you need to be. If your concern is with possible chemical interactions, sorry can't help.
  4. Sep 18, 2012 #3
    Yes, I'm looking for just a solution where there is no chemical reactions occurring in it. I didn't think of that when I posted my question, but I am not looking for something that complex.

    So you're saying it should just be a weighted sum of their volume susceptibilities using their volume proportions as the weight?
  5. Sep 18, 2012 #4
    I see no real problem doing it that way. Whether or not solutions are dilute, magnetic susceptibilities are so low everything is effectively linear to a very good approximation even for high applied field, which is probably not even the case. The one problem I can think of is assuming you are using an AC method (RF frequencies or above). There just may be significant magnetic coupling to molecular orientation. Might then have to watch out for resonance effects re molecular rotation depending on frequency range. Highly unlikely for diamagnetic material but possible in paramagnetic case, but honestly not at all sure and if in doubt seek expert advice. Maybe CRC handbook has such data.
    [This may interest you: http://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=19&ved=0CFIQFjAIOAo&url=http%3A%2F%2Fwww.testronindia.com%2Fpdf_file%2FQuinck.pdf&ei=uOlYUJqEIKWRigeNsoDQCA&usg=AFQjCNHGzorv_Eb42Qqh5KNaO0WzdOIE_g&cad=rja I'm off :zzz:
    Last edited: Sep 18, 2012
  6. Sep 19, 2012 #5
    Slipped my mind at the time, but just nine data points should be sufficient to establish validity of assumption of linear addition of susceptibilities. Plot for substance A three fairly evenly spaced values of susceptance vs w/v concentrations. That will establish linearity applies for solution A, and of course provides means to eliminate background susceptibility of solvent. Repeat for substance B. Finally repeat for a mixed solution of A+B. I would bet big bucks linearity will hold in all cases. Naturally if solution goes cloudy for instance then precipitation reaction has happened and that would ruin things but this would be obvious. One has to make allowance for the usual temperature dependencies, and any systematic and random errors in instrumentation, solution preparation etc. - i.e. make sure 'noise' is low. For most diamagnetic/paramagnetic materials it's not expected that solute/solvent interactions appreciably effects susceptibility of the solute, but at very high concentrations partial solvation may introduce appreciable non-linearities - but again, just do a plot and see. This Wiki article makes a good read: http://en.wikipedia.org/wiki/Magnetochemistry
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