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Volume of Ions by Displaced water
sonicmage
Registered User regular
Registered User regular
hello all.
I am currently writing a paper for Chemistry, and i have been looking to see if there have been any experiments to calculate the volume of halogen Ions in water. is anyone knows of any experiments, by teachers you may have had, or papers written on the same subject, please post them here, because i have been searching the internet and have yet been unsuccessful. this would be much appreciated, thank you.
I am currently writing a paper for Chemistry, and i have been looking to see if there have been any experiments to calculate the volume of halogen Ions in water. is anyone knows of any experiments, by teachers you may have had, or papers written on the same subject, please post them here, because i have been searching the internet and have yet been unsuccessful. this would be much appreciated, thank you.
sonicmage on
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Add a known amount of an element that the ions would create a precipitate with. Such as Na for Cl ions.
Filter the precipitate and dry in an oven. Weigh the resulting precipitate. Since you know the weight of the element added you can easily find the original mass of the halogen ions in water.
There's alittle more to it then that but that's the first experiment I had to do in Analytical Chem. You might try an Analytical Chem Text book as a reference.
Is that what your looking for? I'm not sure what you mean by the size of a single ion?
If you need to calculate the mass or amount of ions in a solution, then precipitation and stoicheometry would work according to Pokeylope's post.
However, I think what you're asking for is how to calculate Ionic Radius, which is done via precipitation, recrystallization, and then x-ray crystallography to find the unit size of a crystal cell. However, I'm not sure how one would go about finding the radius of an unbonded ion in solution.
There's a table on wikipedia of the ionic radiii of varius ions a little down the page at http://en.wikipedia.org/wiki/Ionic_radius
I am not a chemist, but what's wrong with finding the volume of water before you add something, the volume after you add something, measure the masses of what you add so you can calculate the number of ions, then say average size = difference in volume / # of ions? I suppose it would not be exact, but I guess that would depend on your definition of the "size" of the ion?
Alternatively, you could calculate it from quantum mechanics
solid table salt - NaCl - has a polar bond of a fixed length in a crystal lattice - the positive Sodium Ion and the negative chlorine ion are held together much like a the positive and negative ends of magnet.
Water molecules also act like tiny magnets - the two hydrogen atoms having a positive charge, and the oxygen atom displaying a negative charge, although the partial positive and negative charges are weaker than that displayed in the sodium and chlorine ions.
When a salt like NaCl is dissolved in a polar solution like water, what happens is that even though the magnetic attraction between the sodium and the chlorine is stronger than the attraction between the partial charges on the water molecule and the ions, multiple water molecules surround each sodium and each chlorine ion and sort of 'gang up' to overcome the polar bond, and then completely surround the ion, which is now dissociated in the water.
Well, yes, I know that, but if it was like that you wouldn't need to measure anything? But shouldn't there be a simple relation between size and volume difference / # because of this?
Edit: this is the procedure i was talking about, if you have ever heard of someone doing an experiment similar to this, i would love to hear about it, because my chem teacher is thinking that it is an entirely unique experiment that he has come up with
Procedure:
1. Safety Goggles were put on.
2. Volumetric Flask, 400mL beaker, 100mL beaker and paper were collected.
3. NaF(s) was weighed and collected.
4. Distilled water was collected in the 400mL beaker.
5. The distilled water was poured into the volumetric flask to the white line.
6. NaF(s) was poured into the volumetric Flask, the water displacement was measured.
7. NaF(aq) was discarded.
8. Volumetric Flask was filled with distilled water to the new measurement.
9. Distilled water was removed from the volumetric flask using a transfer pipette to the white line.
10. Removed water was placed into the 100mL beaker.
11. Removed water was weighed.
12. Steps 3-11 were repeated with NaCl(s), NaBr(s) and NaI(s).
Sounds a lot like Archimedes' eureka moment where he figured how to determine density of a material by the displacement of water.
You should keep in mind that the water displacement will also be effected by temperature and atmospheric pressure and both should be recorded.