Hi all.

In a plain solution of table salt, left for years undisturbed in a closed jar; which ions will be more abundant (precipitate) at the bottom - Cl or Na ?

Miguel

neither. if they precipitate at all(which they won't assuming the jar is truly sealed and water vapour cannot escape) it will be in equal proportions.

I agree with the alien. The precipitate (or crystals) will be NaCl.

Except that I believe that it will crystalize or precipitate depending on concentration and/or temp, whether or not it is completely sealed.

well, seeing as it is left undisturbed i assumed that also meant temperature distubances. it is true that if you did cool it down the solubility of salt would decrease and there could be precipitation. but assuming constant conditions then there would be no precipitate.

Alien,

What about saturated or supersaturated solutions?

 

Exter,

In what sense is the term "precipitation" being used?

Some, perhaps wrongly, include crystalization with precipitation.

I was assuming that crystalization was included.

dude, the guy just said 'a salt solution'. that could be anything from a single sodium ion and chloride ion floating about to it being mega over saturated.

 

and anyway as i said 'IF they come out of solution it will be in equal proportions'

DrDNA:

Precipitation in the sense of some ions being in higher concentration near the bottom of the container.

To say it simpler, a solution of a teaspoon of salt in a litre of water, steady temperature, capped, undisturbed for a year.

Which ions will sink because of their greater specific weight; Na or Cl ?

Miguel

Which ions will sink because of their greater specific weight; Na or Cl ?

Um, I don't have a Chem degree, but I think you will find that such a thing simply will not happen. There is way too much free energy in the liquid water, which keeps the ions "in solution", more or less permanently. Overcoming this would require a really, really fast centrifuge.

You need to effect some change in the system for ions to precipitate. If you put it in a freezer, it would cause a gradual increase, as it froze, of concentration of the salt. The water turns to ice, and the salt solution doesn't, but collects in concentrated "pockets" within the ice. Eventually it precipitates but thawing out the ice will cause it to all go back into solution. This "precipitation by freezing" works with compounds that have a low solubility, though (so the precipitate remains at the bottom of the container after re-melting).

DrDNA:

Precipitation in the sense of some ions being in higher concentration near the bottom of the container.

To say it simpler, a solution of a teaspoon of salt in a litre of water, steady temperature, capped, undisturbed for a year.

Which ions will sink because of their greater specific weight; Na or Cl ?

Miguel

 

Gotcha.

As InsaneA said, it should be both; NaCl.

Brownian Motion would preclude one or the other from falling to the bottom, although the jar of liquid Looks like it isn`t doing much, on an Atomic scale it`s a hive of activity