Pre-reading for Project 3B
For this project, students are required to extract caffeine (C8H10N4O2), an example of a type of organic weak base called an alkaloid – alkaloid means ‘alkali-like’ from tea by performing 3 forms of techniques: Büchner filtration, Solvent extraction and Distillation using a rotary evaporator.
However, before proceeding on with the project, it is important to have some background knowledge about the concepts used in the project. These are the research that I have done:
What are polar solvents?
Polar solvents have molecules whose electric charges are distributed unequally, leaving one end of each molecule more positive than the other. Usually polar solvents have O-H bond of which water (HOH), methanol (CH3OH) and acetic acid (CH3COOH) are some examples of polar solvents.
What are non-polar solvents?
Non-polar solvents, like carbon tetrachloride (CCl4), benzene (C6H6), and diethyl ether (CH3CH2OCH2CH3), have molecules whose electric charges are equally distributed and are not miscible with water.
What is partition coefficient?
Partition coefficient is the ratio of concentrations of a compound in the two phases of a mixture of two immiscible solvents at equilibrium. It is a measure of differential solubility of the compound between these two solvents.
What is a separating funnel and how does it work?
It is an apparatus used to separate two or more liquids that are immiscible. For example, a mixture of oil and water forms two layers when mixed; as the oil is less dense than water, it floats on the water's surface. To separate them, the mixture is added to a separating funnel. The funnel is usually a glass tube with a tap at the bottom. The tap is turned open to allow the lower layer of liquid to be emptied into a container. When the upper layer of liquid reaches the bottom of the funnel, the tap is turned closed. The layer of liquid that is in the separating funnel can then be emptied into a different container.
click on this link for reference on how does the separating funnel work: http://www.chem.ucla.edu/~bacher/General/30BL/tips/Sepfunnel.html
What is the difference between Büchner filtration and that of the filter paper?
The Büchner filtration is carried out when solids need to be isolated from a solution. It is normally done at a reduced pressure using a Buchner flask and Buchner funnel.
However, the filtration which uses filter paper, or in other words it is also known as gravity filtration is often carried out as part of the process of crystallizing solids. It is generally carried out to remove impurities instead of isolating the solids.
Sources:
http://www.chemicalland21.com/info/SOLVENTS.htm
http://en.wikipedia.org/wiki/Partition_coefficient
http://www.talktalk.co.uk/reference/encyclopaedia/hutchinson/m0097910.html
http://www.chem.ucla.edu/~bacher/General/30BL/tips/Sepfunnel.html
http://www.chem-ilp.net/labTechniques/BuchnerFiltration.htm
http://www.chem-ilp.net/labTechniques/GravityFiltration.htm
