Investigatory projects on chemistry illustrate important concepts of chemistry such as solubility, density and polarity. These projects function to apply a proof of concept to these principles, providing a hands-on approach essential for fully understanding chemistry. The following extraction procedures offer potential insight for students learning chemistry or those simply interested in the subject. All of the procedures can be performed with materials common within a high school or university laboratory, making these projects a useful teaching aid for core principles.
Caffeine extraction involves the use of chloroform or methylene chloride applied directly to coffee bean material. A method that uses 2-propanol, more commonly known as isopropanol, or rubbing alcohol, can be performed at home. First, a water extraction is performed on the coffee beans, in much of a similar way to making coffee, by heating distilled water. This extraction is performed three times. Sodium chloride and calcium hydroxide are then added, raising the pH of the solution to make it basic and increasing the polarity of the solution. This makes the caffeine alkaloid more soluble in the rubbing alcohol than in water. This also functions to make the extraction free of contaminants by forming them into tannin salts, which are not soluble in rubbing alcohol. The pure caffeine alkaloid is then extracted by distilling off the rubbing alcohol until only a small amount remains and then allowing the rest to evaporate, yielding pure crystals.
DNA extraction is a procedure that illustrates the presence of genetic material in living things. For example, peas are mixed with salt and dish soap and then blended momentarily. According to Oracle Thinkquest, "The enzymes in the soap are breaking down the lipid molecules of the cell and nuclear membranes, releasing the contents of the cell, including the DNA." The blended soap/salt mixture is then added to alcohol. Alcohol functions to precipitate DNA out of the solution since it is less dense than the cell material, salt or soap. The DNA strands take on a mucus-like appearance and can then be wrapped around a toothpick.
Extracting Salt From Sand
This experiment functions to extract insoluble sand from soluble salt. A mixture of salt and sand is added to water and stirred. The water is then run through a filter and collected. Once filtered, the water is boiled off, leaving behind the salt that originally dissolved in the water and the sand on top of the filter. The sand and salt can then be weighed to determine the extraction efficiency and per cent composition of salt or sand in the original mixture.