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Growing Sugar Rock Candy

Postby 5dfcdb416cb94c2984d2844653091439 » Thu Jan 17, 2019 8:21 pm

I helped my 7-year old daughter with the crystal seed rock candy experiment listed on this site, and nothing is happening. We followed the directions, and it has been three days since we boiled the sugar water and lowered the strings into the glass jars filled with the solution. How long does it usually take for the crystals to form? My daughter is getting anxious! Thank you for your help!

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Re: Growing Sugar Rock Candy

Postby 17eugenekim » Fri Jan 18, 2019 9:06 pm

Sorry to hear that! Though I haven't done the experiment myself, three days seems more than enough to start seeing results. Did you make any variations or adjustments to the listed procedure? Note that, as written, you are to bring the water to a boil, then add sugar to that high-temperature water until it is saturated. That means as much sugar as possible. If you are just "boiling the sugar water," you may not be getting enough saturation since you are starting with less sugar and simply raising the temperature of the water.

Unless I am mistaken, the core scientific principle here is that the saturation point increases with temperature. So if you have a saturated boiling-hot sugar water solution, and let it cool while the string is inside, it becomes "oversaturated" for that amount of sugar to be in that lower temperature of water. This forces some of the sugar to become "undissolved", coming out of solution to form solid crystals. Therefore, without a sufficiently high amount of sugar in the initial boiling water, you may not see crystals start to form. If you don't have enough sugar, the sugar is not forced out of solution; instead, you just end up with cooled sugary water. I hope that makes some sense.

Hope that helps. Please report back with any new results and/or additional questions!

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