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Isolating & Calculating Purity of Caffeine from Tea Leaves

Isolating & Calculating Purity of Caffeine from Tea Leaves


There are many different types of spectroscopy. Chemists typically use ultra-violet/visible spectroscopy (UV-Vis) to identify compounds and measure their purity. Pharmaceutical scientists use ultra-violet/visible spectroscopy for drug tests and purity assays while environmental chemists use ultra-violet/visible spectroscopy for environmental testing of water and soil.

In this laboratory experiment, your students will extract caffeine from tea leaves. After separation, the caffeine will then be analyzed on the UV-Vis instrument to calculate its purity.  Students will use Beer's Law to calculate target concentrations of their samples and standards and they will use a calibration curve to determine how much caffeine is present in their sample.  Using the final results, students will compare this value to the original mass in order to calculate the purity of the sample.  


    This U-PIK will include enough materials for four student groups.  Suggested group size is 4-5 students.  The U-PIK will include the following:


    • 4 UV-Vis units
    • 4 LabQuest 2 interfaces
    • 5 sets of quartz cuvettes
    • 4 boxes of Kimwipes
    • 5 vials of caffeine standard
    • 1 box of household tea bags
    • 5 sets of volumetric pipets
    • 5 sets of volumetric flasks
    • 5 separatory funnels
    • 5 containers of extraction solvent (methylene chloride)
    • 5 contaners of wash solvent (sodium hydroxide)
    • 5 250 mL beakers
    • 5 pipette bulbs
    • 5 top loading balances
    • 5 100 mL round bottom flasks
    • Assortment of conical/storage vials
    • 5 Ziploc bags of Transfer pipets (10 per bag)+


    In addition, one distillation setup which will include all glassware and heating mantle will be included.  This distillation will recover the methylene chloride extraction solvent.  


    The ultra-violet/visible spectrometer can be easily used to support the concept wavelength and the electromagnetic spectrum.  The known samples will have maximum wavelengths between the ranges of 200-400 nm.  Therefore, this laboratory will support measurements in the ultra-violet region of the electromagnetic spectrum.  


    Students will be required to solve Beer's Law and make various concentrations of samples and standards.  Students will be required to generate a calibration curve using Excel.  They will use the linear regression line to solve for the concentration of caffeine.  Using these values, they will then determine the purity of the caffeine they have isolated.  Therefore a previous discussion of Beer's Law, a calibration curve, the molarity equation, and the dilution equation is recommended.  We encourage you to complete the "Introducton ot UV Spectra" prior to this experiment.  


    The laboratory experiment is best suited for a high school chemistry course.  This experiment will take 2-3 meeting dates to complete.


    Time:  Three laboratory periods are suggested.  One laboratory period will be isolating and brewing the caffeine from the tea leaves.  The second laboratory period will involve students making the standards and samples needed for analysis.  The final laboratory period will allow students to analyze the samples on the UV-Vis instrument. 


    Student Level:

    EXPERT (Grades 11-12) 

  • UV Vis Manual

  • Lab Experiment: Preview Document

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