Transcript
Recrystallization
Abstract:
In this lab, we used the seven steps of crystallization to purify two contaminated substances to return them to their pure state. The seven steps include: 1) choosing a solvent, which is in our case (water.) 2) dissolve the solute, which was (phthalic and Benzoic acid.) 3) decolorizing the solution, and this step is recommended only when the solution changes from colorless to colorful. We used charcoal as it absorbs the color without affecting the solution’s properties. 4) Filtration. 5) Crystallization, in the first activity, it includes heating and cooling the substance to form crystals. For the second activity, we used a vacuum to help us absorb as much liquid as possible. 6) collecting and washing the crystals. 7) Drying the crystals. In this lab, we used water as a solvent, and the percent yield for phthalic acid was 31.3%, and the percent yield for Benzoic acid is 13.8%.
Objectives:
Learn how to purify a solid organic compound using the seven steps of crystallization method.
Remove impurities from a solid (phthalic acid and n-butyl) to allow perfect crystal lattice to grow.
Chemical index:
C8H6O4 H2O
Molecular weight: 166.14 g/mol Molecular weight: 18.01 g/mol
Melting point: 159 °C Melting point: 0.00 °C
Boiling point: 378.3 ± 25.0 °C Boiling point: 100 °C
Phthalic acid water
?C7H6O2
Molecular weight: 122.12 g/mol
Melting point: 122 °C
Boiling point: 250 °C
Benzoic acid
Data and calculation: Activeity#1
Mass of phthalic acid
0.1143 g
Mass of filter paper:
0.0102 g
crystals + filter paper:
0.0460 g
crystals of phthalic acid:
0.0358 g
Percent yield= (dried crystals/ initial weigh) x 100 = 0.0358/0.1143 x100= 31.3
Data and calculation: Activity #2
Mass of Benzoic acid
0.2053 g
Mass of filter paper
0.0102 g
Crystals of benzoic acid + Mass of filter paper
0.0387 g
Crystals of benzoic acid
0.0285 g
Percent yield= (dried crystals/ initial weigh before crystallization) x 100 = 0.0285/ 0.2053 x 100 = 13.8%
Result and Discussion:
After adding the phthalic acid and water to the test tube, it took around 30 min to dissolve, and that is because the hot plate we used for the bath was very slow. After the hot bath water has came to around 70-80 C, the content started to dissolve. It took around 4-6 min for the powder to dissolve after the water bath has been sufficiently heated. The white crystals appeared within 10 minutes of putting the test tube in the ice pack, starting from the top of the tube and down to the bottom. The Benzoic acid was dissolved and crystalized quicker because the hot plate was adjusted, and the vacuum was used to dry it. the percent yield of the phthalic acid was 31.3%, and the percent yield of the Benzoic acid was 13.8%. It was concluded that water is the perfect solvent for both phthalic and Benzoic acid as it helped dissolving them completely. The process of recrystallization was successful and both substances were recovered. However, the unadjusted hot plate could be a source of error because it slowed down the process of dissolving the solute (phthalic/Benzoic acid). We might have achieved better results if the hot bath was hot enough at the beginning of the experiment. As I performed this experiment, I learned how to purify a substance using the seven steps of crystallization. Crystallization can be useful in many fields; for example, it can be used in water filters for both consuming and cleaning uses. It can also be used to produce pure food spices such as table salt.
