Tungol, Zedrick Paul L. Jace Refran2010-10186 Geology 11.1

Title: GROWING POTASSIUM ALUM IN TWO DIFFERENT TEMPERATURES

Objectives of the Experiment: The experiment has 3 main objectives, namely:

Observation of crystal growth Relation of growth to environmental conditions Using data gathered to find optimal growing conditions

Methodology

After acquiring all necessary materials for the experiment, I hacked off 2 pieces of potassium alum

KAl(SO4)2, or tawas from a relatively larger chunk of tawas. Each piece was about 2cm in height, 4cm in length and 1-2cm wide. I dissolved the rest of the tawas in boiling water until it was concentrated and couldn’t dissolve any more. After letting the tawas solution cool, I poured it in two identical 500ml jars. I put green food coloring in one jar and red food coloring on the other. I labeled the “red” jar A and the “green” jar B. I knotted each tawas seed crystal to a popsicle stick and let them suspend into the solution, not touching the bottom of the jar. I put jar A on top of the refrigerator and jar B inside the refrigerator set at 4 degrees Celsius. I took sketches of the crystals at 15 minute, 1 hour, 12 hour, and at 24 hour marks.

Results and Discussion

Looking at the sketches, and also remembering the forms of the crystals at each time mark, I noticed that each crystal grew quite differently from each other. Seed crystal A which grew in normal room temperature, had slower growth than crystal B. However, at the 24 hour mark I saw in crystal A that it had large crystals, smooth to the touch and glossy whereas crystal B had very brittle, small rough crystals.

After looking at a blog entry on the internet I found out that if I let crystal A continue to grow, while removing extra crystals forming on the bottom it would look something like this:

Also, it says that best way to grow crystals (we define “best” as large crystals at the least amount of time) is to grow it at a temperature somewhere between room temperature and water’s boiling point.

In another article, the potassium alum’s crystal shape is said to be an octahedron:

Tungol, Zedrick Paul L. Jace Refran2010-10186 Geology 11.1

Conclusion

The reason why differences in growth in the experiment is due to the difference in temperature in which each crystal was put in. in lower temperatures, faster growth occurs because more nucleation points form, each forming a crystal. Due to the abundance of nucleation points, the crystals are smaller. On the other hand, at room temperature, growth is relatively slow and only a few nucleation points form, creating large crystals (the material is distributed only to a few nucleation points).

References

http://chemistry.about.com/od/crystalrecipes/a/potassium-alum-crystals.htm

http://www.homepages.ucl.ac.uk/~ucfbanf/general/crystal.htm