Crystallization

Exp 3 A, B, D

Crystallization and Melting Points

Conclusion

The solubility curve of ethyl alcohol determines the crystallization of sulfanilamide. At low temperatures the solubility of ethyl alcohol is low, but the solubility is high when the temperature is high. The sulfanilamide dissolves in ethyl alcohol because both are polar due to their functional groups.

There are many sources for error in this experiment. When the sulfanilamide is dissolved in the ethyl alcohol, it is impure. This impurity results in a slight loss of crystals when some of the sulfanilamide is lost to the mother liquor. Also, there is a loss when the crystals come into contact with any surface, whether it is a microspatula, filter paper, the Craig tube, or inner plug. Also, even though it was known how much ethyl alcohol was needed, more was used because the sulfanilamide was not dissolving. Also, the solubility curve shows a 14mg/ml solubility at 0°C, so even in the ice water bath there is a loss of sulfanilamide to the mother liquor. This would have been a loss of crystals as well. All of these errors would account for the low percent yield in both the crystallization experiments.

Melting point analysis of the impure sulfanilamide shows melting starting at 144.0°C and ending at 165.5°C. The wide range of melting point is due to the impure sulfanilamide. The melting point of pure sulfanilamide, according to ChemSpider Database, is 163°C to 167°C. The experimental value of the melting points in part A (160°C - 163°C) and part B (158°C - 165°C) are within the range of the pure sulfanilamide values.