Figure 3: Obtained IR Spectrum Graph of Caffeine

Results:

The predetermined masses provided by the Lipton Tea manufacturers are accepted as the experimental measurements of both tea and caffeine.  The approximate weight of an individual Lipton tea bag is 2.00 ± 0.05 g, containing 55 mg of caffeine per bag.  In an experiment using 2 tea bags, 110 mg is the expected yield of caffeine to obtain.  A 50 mL beaker, along with 2 boiling stones, was weighed in advance with a total mass of 27.56 g during the extraction process.  To extract caffeine, the heated tea solution, along with 5 mL of methylene chloride, was poured into an isolated separatory funnel and inverted to mix the solution completely.  Due to the reaction, pressure built up inside the funnel, requiring the stopcock to be opened to release excess gas following each inversion.  Once settled, the solution separated into 2 layers: the polar, brown tea solution on the top and the nonpolar, clear methylene chloride on the bottom.  The tea separated above the methylene chloride because while the density of water is 0.997 g/mL, the density of methylene chloride is 1.32 g/mL.  Between the two layers sat small bubbles or possible emulsions that restricted the amount of methylene chloride that could be extracted.  Despite this, the methylene chloride/ caffeine layer was effectively drained into the pre-weighed 50 mL beaker and the process was repeated 2 additional times to ensure that all of the caffeine was reacted with.  In doing so, the volatile methylene chloride began to evaporate into the surroundings due to the increased room temperature.  The remaining solution was heated briefly until the volatile solvent evaporated, leaving behind solid caffeine.  When weighed, the beaker, stones, and caffeine rendered a total mass of 27.58 g.  The difference in mass between the initial weight of the beaker and the final product was then the actual yield of caffeine, 0.02 g.  In comparison to the theoretical mass, the experiment provided 18.18% yield of caffeine.

The solid caffeine product was run through an Infrared Spectrometer that uses bond energies to identify chemical compounds.  The spectrometer produced a graph based on measurements of photon energy within a frequency range between 400 and 4000 Hz.  Individual spikes on the graph indicate the unique bond energies of certain functional groups.  For example, the photon energy spike visible around the 3000 Hz frequency represents amine and amide group apparent in caffeine.  The other important spike appears around 1600 Hz and 1750 Hz.  This spike represents the alkene portion of the caffeine molecule.  Using these individual spikes in photon energy, the infrared spectrometer predicts the composition of the compound present.  The spectrometer predicted the probability that the sample produced was caffeine to be 869 out of 1000.  This value has no relation to the purity of caffeine.

Discussion:

As is expected, the percent yield of caffeine was not 100%; however, achieving this goal is impossible.  The mass of caffeine from 2 Lipton tea bags was only 18.18% of the theoretical yield but in consideration of all the factors responsible for error, 18.18% is an acceptable value.  The error in yield results from a number of unavoidable experimental flaws.  The first flaw originates from the reaction between gallic acid and sodium carbonate.  Although the conversion of gallic acid is necessary for the reaction of caffeine and methylene chloride to occur, the phenol anion byproduct of this reaction is responsible for necessary error[1].  When phenolic acids are reverted back into salts, anionic surfactants are produced⁴.  These surfactants are responsible for emulsifying water insoluble materials like methylene chloride.  As a result, large soapy bubbles called emulsions are produced by the polar and nonpolar solutions.  During the extraction phase of this experiment, these bubbles restricted the amount of caffeine released from the separatory funnel resulting in a lesser yield.  Another source of lesser yield originated from techniques used to prevent the contamination of the methylene chloride solution.  While extracting the caffeine, a small layer of methylene chloride needed to be left behind to avoid tainting the final product[2].  By discarding part of the methylene chloride solution, a portion of the caffeine was left behind that affected the overall yield of the product.  The final source of error originates from unpreventable environmental conditions.  As a result of the hot plates used prior to the caffeine extraction phase, the temperature of the laboratory was increased.  Methylene chloride does not usually evaporate at room temperature but being out in the open at an increased temperature triggered the solution to react early on leaving less methylene chloride to react with the caffeine.  This would result in a lesser amount of caffeine extracted from the solution and a lesser yield.

 

 Questions:

1. Look up the structure of caffeine and determine the strongest intermolecular force present.

The strongest intermolecular force in caffeine is the dipole-dipole interaction because of the polarity of the molecule.  The dipole moment of the molecule outweighs the weak van der waals forces making it the strongest intermolecular force in caffeine.

      2.  Why is caffeine more soluble in methylene chloride than in water?

Caffeine is more soluble in methylene chloride than water because both caffeine and methylene chloride are organic substances while water is inorganic.  Although caffeine is capable of dissolving in water by forming hydrogen bonds, the greater affinity that caffeine has for methylene chloride breaks these bonds.

3. Describe the purpose of adding sodium carbonate to the reaction mixture?

The purpose of adding sodium carbonate to the mixture was to alter the chemical structure of gallic acid.  Initially, gallic acid has a slight affinity for methylene chloride that would conflict with the reaction between caffeine and the methylene solvent.  By introducing of a basic sat like sodium carbonate to the solution, gallic acid will be converted into an inorganic, phenol salt that is insoluble in methylene chloride but highly soluble in water.  As a result, methylene chloride extract will contain the highest yield of caffeine alone.