How can I predict whether a salt will retain its paramagnetism in solution?

Submitted by cmlynarski t3_yjfb5h in askscience

I am not a physicist, but am having to brush up on my understanding of magnetism for my biology undergraduate thesis. Thanks in advance for hearing me out:

I am trying to establish whether a paramagnetic salt (manganese II chloride) maintains its paramagnetism when dissolved in a polar, aqueous solution (at which point, it is assumed that it would dissociate into its constituent ions). In a moment of redneck engineering, we placed a small bar magnet on the side of the manganese II chloride saturated solution, to see whether the ions would re-orient themselves in response to this applied field. No change was observed in response to this applied field.

I have a few questions that I'm stumped on:

1. Does the fraction of lone pair electrons in a paramagnetic substance change dependent on the strength of an applied magnetic field?

2. Does the speed at which the electrons relocalize change in response to the magnitude of the applied magnetic field? (ie. maybe we just didn't wait long enough to observe the change)

3. If a polar aqueous solution caused the salt to lose its paramagnetism, then would a non-polar aqueous solution allow for paramagnetic retention? Is there a way to test for either of these?

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Live-Goose7887 t1_ius21bj wrote

It just depends on whether the metal ion's spin state changes when it is aquated. Aqueous manganese(ii) [Mn(H20)6]2+ does remain paramagnetic in solution. I don't understand how the experiment you ran was supposed to detect this though.

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cmlynarski OP t1_iut2bia wrote

Thank you kindly for the reply!

The line of thinking was basically that if we apply a strong enough magnetic source (a field from a bar magnet) that any paramagnetic material would exhibit displacement. My understanding is that only a fraction of the paramagnetic material's electrons (those with the correct spin direction) will show magnetic behaviour, but my assumption was that the fraction would be greater than zero, and would therefore be observable.

Perhaps there is a little more nuance that I'm missing here. Feel free to let me know if you see an error with this assumption or any additional thoughts - it's appreciated.

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Live-Goose7887 t1_iut4xkw wrote

I'm just trying to mentally picture the experiment. Were you hanging a bar magnet from a string and measuring whether it was deflected toward the sample? Or were you pressing the magnet against the container and trying to see if the solution itself was visibly deflected?

While the manganese ions themselves do remain paramagnetic in solution, the chloride ions and more importantly the water itself are diamagnetic. I doubt you could make a solution concentrated enough to see visible deflection of a bar magnet.

There are a few direct ways to measure magnetic moments like using a Guoy balance, an Evans balance, or the Evans NMR method.

Do you mind if I ask loosely why you're interested in it?

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newappeal t1_iuw9yvs wrote

>It just depends on whether the metal ion's spin state changes when it is aquated

How might this occur? Are there ionic species that actually form new molecular orbitals with water in solution?

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DudoVene t1_iurhjkq wrote

hmmm. magnetism needs a difference of electric charge into a molecule. see as H2O itself exhibits a positive charge near the proton and a negative charge near the oxygen.

when you dissolve your salt in aqueous solution, you break the ionic bond between the molecule and form new ionic bond with water. in my mind, you obtain diffuse electric charges in the solution wich are not aligned like in the unsolvated salt. the only possible magnetism effect could come from your 2 hydrated species and could be not related To the initial strenght of the salt.

consequently, non aqueous solution won't dissolve the salt, keeping it in the shape that have the magnetism effect.

I hope others will have knowledge to correct my assumption. and I wish you the best for your studies!

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newappeal t1_iuw9rw4 wrote

You're thinking of electric dipoles, which are different from magnetic dipoles. Electricity and magnetism are, of course, just two manifestations of the same underlying phenomenon, but electric dipole moments and magnetic moments of molecules nonetheless differ in their cause and behavior. The former come from the distribution of electron density in a molecule, while the later arise from unpaired electrons within atomic or molecular orbitals, independent of the shape of those orbitals or the atoms' electronegativities.

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