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Topic: Why wouldn't salt combine with each other when they are smashed into tiny bits?  (Read 3007 times)

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Offline confusedstud

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For instance a bag of salt won't fuse together after a long time. But looking closer at the ions, shouldn't they attract each other? But if I look at it closer, then there could be 2 main possible scenarios one where the Na+ ions on one grain's surface directly face the Cl- ions on the other while the other is whereby the Na+ on one grain's surface faces the Na+ ions on the other. So in the first case, shouldn't there be attraction while on the second shouldn't there be repulsion?

What's keeping them from coming together?

Thanks  :)

Offline curiouscat

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Put it in a tablet press and they will fuse.

Offline confusedstud

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Put it in a tablet press and they will fuse.

Hi could you emphasize on that? What about the repulsion and attraction?

Offline Arkcon

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This is a common misconception that comes up for chemistry students.  They're taught the the crystal is made up of ions that attract one another.  You've come up with the idea that the surfaces should attract.  A common question is, "How does a diamond crystal know when to end, if each carbon atom has 4 bonds, isn't there always a bond free at the surface?"  And the answer is always -- no.  No crystal is perfect at the atomic level.  Faults occur, and add up, sub-trace level impurities of other ions occur, and eventually these add up, until there are no more bonds left to be made, and a neutral crystal surface forms.

Surely, you could melt two large NaCl crystals into liquid NaCl and recrystallize into one crystal.  And you can always slightly melt and sinter the salt into a mass, with heat and or pressure.  A crystal can grow larger from a saturated solution.  But no, solid crystal surfaces don't attract each other and grow bigger.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline confusedstud

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Oh so at the surface the impurities make it neutral? How would that be possible? Since if I place another charged object then it would continue that crystal lattice?

What would happen if I cut a large piece of salt in an empty vacuum and immediately place it back together. Again this has a problem as at the 2 ends of the cut parts would not be neutral at the 2 ends.

Offline Arkcon

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I'm not really sure what the answers to your questions are.  I didn't even have the answer I gave you above, until I was in college and was able to ask a grad-level materials chemist.  His answer was, a little curt, to effect of, "That just doesn't happen."  Along those lines:

Oh so at the surface the impurities make it neutral? How would that be possible? Since if I place another charged object then it would continue that crystal lattice?

Where will you get another charged surface?  You not conflating a light static charge, or a current induced charge, with atomic charges, are you?  Because that's not the same thing at all.

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What would happen if I cut a large piece of salt in an empty vacuum and immediately place it back together. Again this has a problem as at the 2 ends of the cut parts would not be neutral at the 2 ends.

I don't know.  I said that the internal faults add up to a neutral surface.  Perhaps, if a crystal is split, the crystal rearranges to a neutral surface.  We are at temperatures above absolute zero, so the crystal could rearrange.  What do you mean by vacuum?  How does that help?  Or is that some sort of magic status you've just applied to the question to be cool?  If we could achieve absolute zero, we might be able to saw a crystal, and then there might be exposed charges, Na+ on one half, Cl- on the other half.  Then again, that might not occur for another reason.  At any rate, we can't achieve absolute zero, so its not worth worrying about.

Like I said, I was in college, and I was still thinking, "But what if we had a diamond with only 100% pure carbon in it, and no flaws, when will it end?"  But the answer was, that simply does not happen.
« Last Edit: February 01, 2013, 01:04:49 PM by Arkcon »
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline curiouscat

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Oh so at the surface the impurities make it neutral? How would that be possible? Since if I place another charged object then it would continue that crystal lattice?

What would happen if I cut a large piece of salt in an empty vacuum and immediately place it back together. Again this has a problem as at the 2 ends of the cut parts would not be neutral at the 2 ends.

One productive way out of these conundrums is start thinking how you'll do this. Do you have lattice sized objects? How will you see if they stuck or not? How empty is a vacuum you can get? etc.

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