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Crystal Lab

The document summarizes an experiment conducted by Crystal Lab to determine the effect of molecular weight on crystallization. They dissolved four chemicals - copper sulfate, ammonium sulfate, aluminum potassium sulfate, and citrine (which was actually ammonium phosphate) - in water and grew crystals on wood splints over three days. They found that copper sulfate, which had the median molecular weight, produced the largest crystals at 0.94g, while aluminum potassium sulfate with the highest molecular weight produced the smallest crystals at 0.24g. This result contradicted their hypothesis that higher molecular weight chemicals would produce larger crystals. They acknowledged errors in assuming citrine was actual citrine and losing part of the citrine crystals during weighing.

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168 views2 pages

Crystal Lab

The document summarizes an experiment conducted by Crystal Lab to determine the effect of molecular weight on crystallization. They dissolved four chemicals - copper sulfate, ammonium sulfate, aluminum potassium sulfate, and citrine (which was actually ammonium phosphate) - in water and grew crystals on wood splints over three days. They found that copper sulfate, which had the median molecular weight, produced the largest crystals at 0.94g, while aluminum potassium sulfate with the highest molecular weight produced the smallest crystals at 0.24g. This result contradicted their hypothesis that higher molecular weight chemicals would produce larger crystals. They acknowledged errors in assuming citrine was actual citrine and losing part of the citrine crystals during weighing.

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© © All Rights Reserved
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Crystal Lab Trevor Mendola, Dom Prentice, Jacob Carmody

Research:

Crystallization is the process of changing a solid product into an aqueous solution through
temperature change. The process starts when a product is dissolved in a boiling solvent. Once a
product is dissolved and after it is cooled, it will appear as crystal-like solids in the liquid
product. This process can only occur if the solute is insoluble at room temperature, and soluble at
a higher temperature. An important factor in crystallization is the molecular weight of the
chemicals, as when a chemical has a higher molecular weight the amount of crystals forming
increases.

http://www.wiredchemist.com/chemistry/instructional/laboratory-tutorials/recrystallization
https://www.sciencebuddies.org/science-fair-projects/project-ideas/Chem_p082/chemistry/how-
to-grow-the-best-and-the-largest-crystals#background
https://www.sciencedirect.com/science/article/pii/S0142941806001590

Question: What affect does molecular weight have on crystallization?


Hypothesis: Higher molecular weights will produce larger crystals faster.
Material List:
- 10.00 g Copper sulfate
- 10.00 g Ammonium sulfate
- 10.00g Aluminum potassium sulfate
- 10.00g “Citrine"
- 4 100mL beakers
- Source of water
- Five wood splints
- 4 weigh boats
- 2 hot plates
Procedure:
1. Fill four beakers with 80 mL of water each
2. Place beakers on hot plates
3. Turn hot plates to high temperature
4. Pour 10.00g of Copper sulfate into weigh boat
5. Pour 10.00g of Ammonium sulfate into weigh boat
6. Pour 10.00g of Aluminum potassium sulfate into weigh boat
7. Pour 10.00g of “Citrine” into weigh boat
8. When water begins to boil, pour chemicals into beakers (1 chemical per beaker)
9. Stir beakers until chemicals dissolve
10. Turn off hot plates
11. Place 1 wood splint into each beaker
12. Place beaker on safe surface to cool for 3 days
13. Weigh mass of one dry wood splint
14. Dry off water-logged portion of each crystalized wood split
15. Weigh mass of each crystal (Weigh crystal-wood splint and subtract weight of wood splint)
16. Record mass of each crystal
17. Properly dispose of substances
Data:
Mass of Crystals after 3 days
- “Citrine” = 0.71 g
- Copper sulfate = 0.94 g
- Aluminum potassium sulfate = 0.24 g
- Ammonium phosphate = 0.81 g
Analysis:
There was no distinguishable trend in the data. Given the three molar masses tested, the
substance with the median molar mass, copper sulfate, proved to be the best for growing crystals,
0.94g in three days. The substance with the greatest molar mass, aluminum potassium sulfate,
produced the smallest crystals by a vast margin, 0.24g in three days. These results are drastically
different from our research and hypothesis; greatest molar mass should produce the largest
crystals however the experiment proved otherwise. Although the errors in our experiment were
not correlated with the aluminum potassium sulfate, they still are notable. When performing the
experiment, we thought we were using citrine but did not realize that it was pseudo-citrine
(orange dyed ammonium phosphate). Also, when preparing the crystals to be weighed, a chunk
of “citrine” fell off of the splint into the solution, thus it was not measured. A bit more reading
could have been done to realize that we only technically were using three substances before we
performed the lab.
Conclusion:

In our lab we compared four different chemicals to see which could form the best crystals on
wooden splints. The chemicals we used were “Citrine” (we thought it was actual citrine but it
turned out to be ammonium phosphate), copper sulfate, aluminum potassium sulfate, and
ammonium phosphate. An error that occurred was Citrine is ammonium phosphate. First, we
created our chemical solutions in different beakers. Then we stuck the wooden splints into the
chemicals and let it sit there for three days. When we came back we noticed many crystals on the
wooden splints. Then we weighed each crystal and compared them to one another. We noticed
our hypothesis was incorrect because we thought if the chemical had more molar mass than that
would mean more crystals. Instead the solution that had the most molar mass had the least
amount of crystals.

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