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Recrystallization Lab Essay

Recrystallization is a method used for purifying solid organic compounds. It is the most efficient method to purify and remove impurities from a solid to allow a crystal to grow. The method is when the solute in a hot solvent yields to a solution. Once the solvent cools, the solution is saturated with respect to the solute, which is when it recrystallizes. A crystal is the end result of the method and it is a single pure substance with the impurities being excluded from it. The recrystallization method can be broken down into seven steps: 1) Choosing the solvent, 2) Dissolving the solute, 3) Decolorizing the Solution, 4) Filtering suspended solids, 5) Recrystallizing the solute, 6) Collecting and washing the crystals, and 7) Drying the product. Activated Charcoal is used in Recrystallization to absorb the impurities that are in the solution.

Experimental Section

1) Recrystallization of Phthalic Acid

2) Recrystallization of Benzoic Acid
3) Recrystallization of Naphthalene
Table of Chemicals

Melting point
Boiling Point
Molar Mass
Color
Phthalic Acid
230°C
Decomposes
166.13 g/mole
White
Benzoic Acid
122.4°C
249.2°C
122.12 g/mole
Not available
Naphthalene
80.2°C
218°C
128.19 g/mole
white

Results

Phthalic Acid
Benzoic Acid
Naphthalene
Mass
.143 g
.126g (w/ out water)
.098g (w/ water)
.439g
Percent Recovery
71.5% (0.143g/0.2g)
252% (.0126/0.05g)
196% (0.098g/0.05g)
43.9% (0.439g/1.0g)
Melting Point
220°C
110°C (w/ out water)
105°C (w/ water)
70°C

Discussion

The percent recovery of Benzoic Acid is way above 100%. This indicates that an error was performed during the experiment. Phthalic Acid melted just 20°C less than the standard melting point for Phthalic Acid. Naphthalene melted 10°C less and Benzoic Acid also did not reach the standard melting point. Reasons for a low percent Recovery for Phthalic Acid and Naphthalene is probably because not all of the solid were collected when filtered out.
Reasons for Benzoic Acid being over 100 % is probably because there was an excess of solute and it was not filtered out correctly.

Conclusion

To conclude, the experiment was successful in creating crystals and removing them from impurities. Only fault was not taking out enough of the crystals to get the right percent recovery. The techniques for recrystallization can be used for any chemicals as long as there is a solvent that it can mix with and it is an impure compound.

References

Weldegirma, Solomon. Laboratory Manual: CHM 2210L and CHM 2211L. Tampa: Chemistry Department, 2014. Print. “Phthalic Acid Msds.” Science Lab. N.P., n.d. Web. 30 Sept. 2014 “Recrystallization Technique.” – [www.rhodium.ws]. N.p., n.d. Web. 29 Sept. 2014.


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