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Q & A: ionic solution neutrality

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Most recent answer: 10/22/2007
Q:
When salts dissolve in H2O, my understanding is that the electrovalent bond is broken, since the H2O molecules are strongly attracted to the positive and negative ions of the salt. But when seawater is analyzed for ion content, there is almost an exact complement of negative to positive ions present in the samples - except in some limited regions where external forces may come into play.

Is a magnetic attraction the only force that maintains the relative balance of negative to positive ions in solution? Or is it some weaker electrovalent bond? Or is it just some random occurrence?
- Zander Mills (age 17)
USA
A:
This problem is really much simpler than the way you are thinking about it. If there were many more positive ions, then the solution would very strongly attract negative ions and vice versa. So itís very hard for some object to stay charged up when there are any paths for positive or negative charges to enter or leave it. Thatís plain old electrostatics. Magnetism plays essentially no role in this.

The electrical force is long-range, so if, for example, a Na+ happens to stick to the more negative part of a neutral H2O, that doesnít get rid of the net positive charge. The whole clump still attracts negative charge.

Then there is also a name convention: A substance which disolves in water with one of the ions being H+ is called an acid, if one ion is OH- itís called a base. If both ions are something else, not a constituent of water, then itís called a salt. Perhaps when you say the list of ions adds up almost to neutrality, you mean that the net concentration of the water ions (H+  and OH-) is very low compared to the total ionic concentration in sea water.

Mike W.


(published on 10/22/2007)

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