[sciguy]

Is it possible to prepare a solution containing only one ion?  For example, if I were to dissolve a salt in water, would it be possible to filter out the cation leaving only the anion behind?  I can't think of any way to do this because if some compound were dissolved to precipitate out the cation, it would introduce another cation to the solution.  Thanks for the *delete me*

[confusedstud]

A solution must be electrically neutral. So no it is not possible to simply remove a cation from a solution leave only the anion back or vice versa.

[fledarmus]

There have been a lot of attempts to do something very similar to this over the years. Some of the more elegant solutions involved trying to build very stable, hindered anions with metal cations and mixing them with concatenating cage structures that would isolate the cations and precipitate them or sequester them in some way from the solution. As far as I know, however, nobody has succeeded yet in isolating a free ion.

[dazza95]

Because a solution has to be neutral, no one has sucessed in making one with just one ion.

[fledarmus]

Because a solution has to be neutral, no one has sucessed in making one with just one ion.

It's that "solution has to be neutral" thing that people keep pushing against. Does a solution truly have to be neutral? Granted, a non-neutral solution would be much higher in energy than a neutral solution and exposure to any pathway that would allow it to neutralize would result in a fast spontaneous neutralization, but is there a way to isolate one ion sufficiently strongly to overcome that energy? Unless the energy holding the two ions together is infinite, it may be possible, by blocking every possible neutralization pathway, to make a one ion solution. After all, it can be done in the gas phase...