Afterwards we used acetone-petroleum ether for recrystallization and the vacuum apparatus for filtration to obtain pure caffeine. At the end the melting point of the pure caffeine was obtained. (Reference: Organic Chemistry Laboratory Manual) Experiment Scheme: We used 250 mL of water and 20. 08 g of pre-ground coffee in the espresso maker to make the coffee. After we collected the coffee into a beaker that had a 6. 0 g of CaCO3 in it. We heated the mixture to about 70 °C for about 10 minutes on a hot plate and the let it to cool down to room temperature.
Then we used the fritted funnel with Celite, which is a filter aid inside the filter for filtration. If foaming occurred, vacuum had to be removed right away until foaming disappeared. Afterwards, the filtrate was transferred evenly into 2 separatory funnels, and extracted with 4*20 mL of dichloromethane (CH2Cl2).
The separatory funnels were rolled carefully and not shaken. After the extractions, the organic (bottom) layer was collected. The combined organic layer then was dried with anhydrous magnesium sulfate (MgSO4).
The insoluble solids were filtered and removed. The filtrate then was transferred into a 250 mL round-bottom flask. Then a rotary evaporator was used to evaporate the solution. This then formed the crude caffeine. The crude product was recrystallized with acetone-petroleum ether. First the crude product was dissolved in a small amount of hot acetone, and then petroleum ether was added to make the solution to become cloudy, which was followed with cooling the solution in an ice bath. A Hirsch Funnel was used to filter the crystals and weigh them.
The Essay on Osmosis Of Potatoes In Different Sucrose Solutions
The aim of this experiment is to test whether more water moves out of a potato when it is placed in a sweeter sucrose solution than a potato in a less sweet solution. The hypothesis of the experiment is that we expect more water to move out of the potato placed in the sweet solution than the potato placed in a less sweet solution. Independent variable: concentration of sucrose, concentrations: ...
Therefore, the addition of sodium carbonate helps the acid to convert to their sodium salts, which are highly soluble in water 2. What are some possible explanations for why the melting point of your isolated caffeine may be lower than the literature value (236) This may because of the isolated caffeine produced by the experiment was containingother elements which cause the caffeine not 100% pure. Thus, lower the melting point of the caffeine. Your caffeine was not pure and probably still had traces of whatever was used to separate it. This depresses melting point.
The literature value is at the upper end of the melting range. There is also the possibility you did not calibrate the melting point appartus with AR grade compound in the melting range. Melting points should always be reported as a range. Maybe during purification process was not perfect, and there were impurities in the caffeine that were affecting the melting point. The melting point is depressed due to impurities in the sample. The caffeine is usually not 100% pure, maybe improper isolation procedure and also the impurity is likely solvent.
