Beer’s Law Experiments, Spectrophotometric Titrations, Kinetics

1. Beer’s Law

There are literally dozens of pages of references in J. Chem. Educ. regarding Beer’s Law analysis dating back to 1932. Some of these articles describing methods are pretty straight forward. Others involve mixtures, color subtraction, new reagents, new light sources, computer simulations, and non-monochromatic light.

We often think of Beer’s Law in terms of using a calibration curve proportional to analyte concentration in the determination of the analyte. However, the concept behind Beer’s Law – the proportionality between concentration and absorbance – is used in reaction kinetics, equilibrium constant determination, and in color the analysis of mixtures via color addition and subtraction. The concepts behind Beer’s Law are also used in fluorescence and scattering experiments, both of which involve a proportional relation between light intensity at an angle to the source light and concentration of analyte.

MicroLab’s FS-522 unit with FASTspec allows for any of these approaches to be used easily.  And many of these experiments can be adapted to use the Model 112 light sensor.

Detection of Nitrite in Water Using Minoxidil as a Reagent
Mario González-Jiménez, Jorge Arenas-Valgañón, Isaac F. Céspedes-Camacho, Juan Carlos García-Prieto, Emilio Calle, and Julio Casado
J. Chem. Educ., Articles ASAP (As Soon As Publishable)
Publication Date (Web): June 10, 2013

The Equilibrium Constant for Bromothymol Blue: A General Chemistry Laboratory Experiment Using Spectroscopy
Elsbeth Klotz, Robert Doyle, Erin Gross, and Bruce Mattson
J. Chem. Educ., 2011, 88 (5), pp 637–639

Gibbs Energy Changes during Cobalt Complexation: A Thermodynamics Experiment for the General Chemistry Laboratory
Michael J. DeGrand, M. Leigh Abrams, Judith L. Jenkins, and Lawrence E. Welch
J. Chem. Educ., 2011, 88 (5), pp 634–636

Waters of Hydration of Cupric Hydrates: A Comparison between Heating and Absorbance Methods
Rebecca Barlag and Frazier Nyasulu
J. Chem. Educ., 2011, 88 (5), pp 643–645

Two Methods of Determining Total Phenolic Content of Foods and Juices in a General, Organic, and Biological (GOB) Chemistry Lab
Lee Alan Shaver, Sam H. Leung, Amy Puderbaugh, and Stephen A. Angel
J. Chem. Educ., 2011, 88 (4), pp 492–495

A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin
Simeen Sattar
J. Chem. Educ., 2011, 88 (4), pp 457–460

Spectrophotometric Determination of Iron(III)–Glycine Formation Constant in Aqueous Medium Using Competitive Ligand Binding
Rajendra Prasad and Surendra Prasad
J. Chem. Educ., 2009, 86 (4), p 494

A New Colorimetric Assay of Tabletop Sweeteners Using a Modified Biuret Reagent
Christopher J. Fenk and Nathan Kaufman , Donald G. Gerbig Jr.
J. Chem. Educ., 2007, 84 (10), p 1676

Redox Titration of Ferricyanide to Ferrocyanide with Ascorbic Acid: Illustrating the Nernst Equation and Beer–Lambert Law
Tina H. Huang , Gail Salter , Sarah L. Kahn and Yvonne M. Gindt
J. Chem. Educ., 2007, 84 (9), p 1461

Using Visible Absorption To Analyze Solutions of Kool-Aid and Candy
Karen E. Stevens
J. Chem. Educ., 2006, 83 (10), p 1544
Here is a determination by the method of continuous variations (Job’s Method):

Salicylate Detection by Complexation with Iron(III) and Optical Absorbance Spectroscopy. An Undergraduate Quantitative Analysis Experiment
Kendra R. Reid and Mark E. Meyerhoff , Jeremy T. Mitchell-Koch
J. Chem. Educ., 2008, 85 (12), p 1658

2. Photometric Titrations

These offer some good chemical systems for photometric titrations, either alone or in combination with other methods. The FS-522 with its onboard FASTSpec spectrometer plus an autopipet make the process much simpler than the methods in the references suggest. The 522 unit can be placed on a magnetic stirrer for rapidly generating homogeneous samples with each addition. MicroLab’s cylindrical vials allow for efficient stirring and remarkable reproducibility – typically better than +/- 0.001 AU – between samples The FASTSpec software makes the entire process easy to set up and perform.

Future releases of the MicroLab software will have specific wavelengths from the FASTSpec as ordinary sensors in the regular software so that photometric titrations and other spectral processes can be integrated into experiments that take advantage of other sensors – drop counter, pH/mV/ISE, temperature – and closed loop experiments with logical control. Stay tuned.

Analysis of Citric Acid in Beverages: Use of an Indicator Displacement Assay
Alona P. Umali and Eric V. Anslyn, Aaron T. Wright, Clifford R. Blieden, Carolyne K. Smith, Tian Tian, Jennifer A. Truong, Caitlin E. Crumm, Jorge E. Garcia, Soal Lee, Meredith Mosier and Chester P. Nguyen
J. Chem. Educ., 2010, 87 (8), pp 832–835

A Low-Cost Device for Automatic Photometric Titrations
Fábio R. P. Rocha , Boaventura F. Reis
J. Chem. Educ., 2000, 77 (2), p 258

Determining the critical micelle concentration of aqueous surfactant solutions: Using a novel colorimetric method
Kenneth G. Furton and Arold Norelus
J. Chem. Educ., 1993, 70 (3), p 254

Potentiometric and photometric methods for determining the solubility of lead iodide
Gary W. Rice
J. Chem. Educ., 1990, 67 (5), p 430

Photometric titrations
Arthur L. Underwood
J. Chem. Educ., 1954, 31 (8), p 394

See also the MicroLab newsletters, especially Volume II, Number 1, for further discussion.

MicroLab also has a photometric titration experiment as a lab handout suitable for analytical or honors first year chemistry. The reaction is between permanganate and oxalate ions and features a mechanism in which the Mn(II) product catalyzes the reaction.


3. Kinetics

The most common experiments in kinetics in the introductory laboratory involve food coloring dyes and bleach or crystal violet with NaOH. These are generally first order in each reagent. Some food dyes do not obey Beer’s Law above a certain concentration, so it is important to check the linear Beer’s Law response ranges before doing the kinetics experiment. MicroLab has experiments involving crystal violet with NaOH and Red #40 with commercial bleach. Analytical text/lab books have methods for kinetic detemination of substrate such as glucose with glucose oxidase. JCE has quite a few of these.

Here are a few more from JCE that would work really well with the FS-522 unit and FASTSpec in kinetics mode.

Speaking of…this first one describes the classic crystal violot – NaOH experiment.

Colorimetric chemical kinetics experiment
Gerald Corsaro
J. Chem. Educ., 1964, 41 (1), p 48

A microcomputer-interfaced kinetic spectrophotometry experiment
J. V. Badding , R. C. Barile and L. P. Michiels
J. Chem. Educ., 1986, 63 (9), p 806

Kinetics of Alcohol Dehydrogenase-Catalyzed Oxidation of Ethanol Followed by Visible Spectroscopy
Kestutis Bendinskas , Christopher DiJiacomo , Allison Krill and Ed Vitz
J. Chem. Educ., 2005, 82 (7), p 1068

Determination of glucose: A kinetics experiment for the analytical course
E. Clifford Toren Jr.
J. Chem. Educ., 1967, 44 (3), p 172

An Improved Method for Studying the Enzyme-Catalyzed Oxidation of Glucose Using Luminescent Probes
Matthew Cuber and J. N. Demas , William D. Bare and Chi V. Pham
J. Chem. Educ., 2007, 84 (9), p 1511