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Author Topic: Sugar crystals  (Read 251 times)

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jade.en.laura

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Sugar crystals
« on: June 13, 2018, 04:55:06 AM »

Recently we made sugar crystals in a glass by oversaturating a solution of sugar and water. We balanced a pencil with a string tied to it on the glass, letting the string down in the solution without it touching the sides of the glass, and let it sit for about 2 months. Instead of the sugar crsytals forming on the string, they have covered the surface of the solution and some crystals have formed on the bottem of the glass. I was wondering if anyone could explain to be why the crystals did not form on the string.
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Corribus

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Re: Sugar crystals
« Reply #1 on: June 13, 2018, 07:52:45 AM »

You may not have heated the solution enough. If there are any undissolved sugar at the bottom or sides of the glass, that's where the crystals will preferentially grow. Also, I have found it is helpful to drag the string in a little bit of sugar before hanging it - this way you seed the string. Although, this may result in smaller crystals.

Other things that may impact the ability of crystals to grow include the purity of your sugar, the purity of the water, the cleanliness and smoothness of your glass, and the material of which the string is made. Crystal growing is a very finicky process.
« Last Edit: June 13, 2018, 08:16:54 AM by Corribus »
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Arkcon

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Re: Sugar crystals
« Reply #2 on: June 13, 2018, 03:07:33 PM »

What happened is what is typical for crystallization for analytical purity, or for production of a chemical or a pharmaceutical.  The solution precipitates its excess because of something you did, and by letting it happen slowly, you got large crystals.  There's ore here: https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/crystallization  But your textbook is probably adequate to tell you more than you need to know.

The problem is, you wanted the rock candy on a string demonstration, and you didn't get it.  Problematical.  Look up how crystals grow.  Try to answer this question:  Why didn't you get crystals on both the string and the bottom of the jar?
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