Crystals and different solids

[katculp]

I am doing my science fair project using different solids to grow crystals. I am using: Borax, Baking Soda, Epsom Salt, Sea Salt, and Granulated Sugar. I made my supersaturated solutions 2 days ago, and the Borax and Baking Soda are growing like crazy. The other 3 are not, there is nothing so far. I planned for my experiment to last 7 days. I am wondering if the Epsom Salt, Sea Salt or Granulated Sugar will grow anything on time. I think I should mention that I am using craft chenille stems, or "pipe cleaners". I don't know if this makes a difference.

I understand why crystals form, but I am having a hard time finding any information on why some solids make bigger crystals than others, and why some grow faster. I would really like to explain this for all the solids I made supersaturated solutions with. I thought Borax would make the most, and I was right. The problem is I have no idea why and I cannot find anything to explain it.

Thank you for your help.

Katherine
5th Grade

[kgudger]

Hi Katherine and Welcome to the Forums!

I'm not an expert in this area, but I did some searching. I found a couple of things that might help you. First I found this quote about crystallizing sugar:

Sugar molecules, which are relatively large, are slow to find the proper positions for crystal formation. Meanwhile, collisions with water molecules keep knocking them apart.

I also found out that you might have to wait "about 2-3 weeks" for the sugar to form crystals. Apparently salts depend on evaporation to increase their concentrations, and may take even longer.

If the solubility doesn't change much over your temperature range, you will have to rely more on evaporation to cause your crystals to grow (e.g., salt crystals). In the one case, you cool your solution to stimulate crystal growth. In the other case, you keep the solution warm to speed up evaporation.

From my searching, it seems that you might want to look at how much more solute (borax, salt, sugar, e.g.) will dissolve as the temperature increases (solubility index) and see how this relates to how fast the crystals grow. I also found out that the faster the crystals grow, the smaller they tend to be.

I hope this helps.
Keith

[katculp]

Hi, Keith!

Thank you very much for this information. I am surprised that even now, neither one of the salt solutions have made one single crystal on the pipe cleaner. The only thing that is growing from either of the salts is the sea salt. It has some tiny crystals on the string attached to the pipe cleaner, and that is all. I wonder if the metal in the pipe cleaner is reacting with the salt preventing the crystals from growing?

The borax and baking soda solutions are still growing wild, but not the others. It's frustrating because I can't explain exactly why! There must be a specific reason somewhere, it seems to be the most popular solute in this type of project. It's crazy that the experiment is all over the place on the internet, but there is no reason to explain why it grows like it does to go with the project.

Where did you find the information you gave me in your post? It definitely answers a few of my questions. I want to be able to include the facts in my bibliography.

Thank you so much for your response.

[kgudger]

HI:

Here are the links:
http://preparatorychemistry.com/Bishop_ ... urated.htm
http://chemistry.about.com/od/growingcr ... rystal.htm

Keith