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Name: Javairia
Status: student
Grade: 4-5
Country: USA
Date: Spring 2010



Question:
I did an experiment on Does Temperature Affect Growth of Crystals. I used three jars filled them with saturated solution made of Borax. I placed strings in each jar. Air tight those jars and placed one jar in refrigerator, one at room temperature and one in an ice bath. I left them for 5-6 hours, I thought that more crystals will grow in room temperature but to my surprise most crystal grew in cold (refrigerator). I repeated it three days in a row but got the same answer, I wanted to know why does crystal grew more in cold temperature.


Replies:
Hi Javairia,

Your borax solution was saturated at room temperature when you made it, but remember that the amount of solute (borax, in your case) that can be dissolved to make a saturated solution, is much less as temperature falls. So what started out as a saturated solution of borax at room temperature, becomes a supersaturated solution at low temperature. Crystal growth from a supersaturated solution proceeds much more rapidly... sometimes it is so fast that you can actually see the crystals form as you watch.

Regards,
Bob Wilson


Hi Javairia,

You mention saturated solution, so I am going to assume you understand the concept of solubility. For sodium borate, the warmer the water, the higher the solubility of sodium borate. The solubility for sodium borate is actually 4 times higher in near-boiling water than near-freezing water. Thus, if the solution you made at room temperature was saturated, it would be supersaturated at a colder temperature, and the crystals will fall out of solution until it reached its (lower due to being colder) saturation point. You may still get a few crystals from the room temperature solution, but not as many because it is still near its saturation point -- any crystals that might randomly form may just return to solution. If you were to warm the jars, (or make your saturated solution using colder-than room temperature water) the crystals would redissolve over time and you would have few or no crystals.

Hope this helps,
Burr Zimmerman


Hi Javairia,

Was the solution saturated once the temperature changed? Usually a substance is more soluble in warmer water than in cooler water. Thus, when you put a solution that is saturated at room temperature into a refrigerator and it cools it can become supersaturated.

Greg Bradburn



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