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Chemistry Question: - RonO's Ramblings

Mar. 9th, 2009 08:21 pm Chemistry Question:

Looking at the progress of Derrick's crystal growing experiment, I'm beginning to wonder if acetone or vinegar (acetic acid) prevents the formation of crystals for either (or both) sugar or salt.

The experiment that is being run is to attempt to make crystals by the string in solution method out of solutions of sugar and salt dissolved in both acetone (100% according to the bottle) and distilled vinegar (5% acetic acid). After more than 48 hours the only changes we've seen is a noticeable reduction in the volume in all 4 containers, but more so in the acetone containers, and little crystals of salt above the original line in the vinegar/salt solution.

Of course it may just be too early to see any seed crystals forming by this method.

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Comments:

From:mbcrui
Date:March 10th, 2009 12:21 pm (UTC)
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We had a hard time with growing crystals. Yoou need to supersaturate the liquid and we were no where close.
From:rono_60103
Date:March 10th, 2009 03:58 pm (UTC)
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In at least one case, the solution has to be pretty much saturated, there is salt sitting at the bottom of the container. On the other hand, that may in its self be a sign that something is wrong and the salt came out of solution too soon.
From:qnofhrt
Date:March 10th, 2009 08:44 pm (UTC)
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What are the salts and which is in what solvent?
From:rono_60103
Date:March 10th, 2009 10:07 pm (UTC)
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He has both table salt (NaCl) and white sugar (glucose?? I have no idea of the chemical formula) dissolved in both the acetone and the vinegar. 4 total tests (and no control).
From:daddy_guido
Date:March 11th, 2009 05:03 am (UTC)

C12H22O11 = 2 C6H12O6 − H2O

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From:nolly
Date:March 10th, 2009 09:35 pm (UTC)
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We never could get the rock candy thing (supersaturated sugar-water solution + string) to work when we were kids. Don't know if our solution wasn't as super-saturated as we thought, or what.
From:daddy_guido
Date:March 11th, 2009 04:56 am (UTC)
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Heat, my boy.

When I used to make rock candy, I would boil me some water, and stir in sugar while it boiled, till it wouldn't take no more. Quickly pour boiling solution into jar, place lid with string hanging down into jar - DO NOT TIGHTEN LID.

Let cool - when room temp is reached you may already see crystals forming on string. you can then screw on the lid and let nature take it's course.

Why the hell are they having kids use Acetone when both salt and sugar are dissolvable in water? The vinegar i can understand but acetone is an extremely dangerous solvent.
From:robot_grrl
Date:March 11th, 2009 05:10 pm (UTC)
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Actually, the experiment was to see if by using a solvent with a higher evaporation point you could grow larger crystals. The problem being that salt and sugar do not dissolve well in acetone. So these solutions were affected by the saturation levels, not just solvent evaporation rates. There are salt crystals formed on the string above the vinegar level though.
From:daddy_guido
Date:March 11th, 2009 07:28 pm (UTC)
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I guess my point was - they could have done the evaporation test using something safer, like methyl alcohol.
From:robot_grrl
Date:March 13th, 2009 12:18 am (UTC)
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Ahhh, but it was I who decided to use acetone - not the school - it was cheap and it was there. And, I'm sure kiddo would have wrinkled his nose just as hard at the smell of methanol and he did with the acetone.