Spectrophotometry & Kinetics

Simulation

This simulation is meant to demonstrate aspects of:

1. Spectrophotometry & Beers Law.
2. Elementary irreversible batch kinetic reactions.

Either may be demonstrated independently. A summary of this system and its governing equations may be found below the simulation. Set up your initial conditions at the bottom of the applet and press play to run the reaction simulation in "real-time". Press fast forward to run as quickly as possible. Mouse-over each input option to see a description of that option or variable. Operation instructions are below.

· Beer Lambert Law · T = V / Vmax = 10-A A = wCAεA · Reaction Kinetics · α A + β B → C R = CAα CBβ k dCA / dt = -α R 0 s 0                V: T: A: t: 0 s CA: CB: CC: Spectrophotometer Kinetics V T A T (true) A (true) V T A CA CB CC Chemical A Spectrum ↺ Random Beta Carotene Chlorophyll a Malichite Green Crystal Violet   y ln(y) y-1 y-2 Spectrophotometer & Kinetic Properties Spec. Parameters w cm λ nm PL % Vmax V Spec. Data V V T % A Concentrations CA0 M CA M CB0 M CB M CC M Kinetic Parameters εA M-1cm-1 α β kr t s

Instructions

Relevant Screencast Videos:

• Spectrophotometry I Lecture- Introduction to Light and Absorbance
• Spectrophotometry II Lecture - Beers' Law & Its Derivation
• Example Simulation Problem - Solving for the Cuvette Width

In this reaction, Molecule A absorbs visible light based on its absorption spectra seen in the "Spectrophotometer" plot above. As such, this simulation may be used to approximate the behavior of a spectrophotometer when altering A's concentration (C_A), its molar extinction coefficient (ε), or the sample's width (w).

Molecule A also reacts with Molecule B to form C. Neither B nor C absorb light and so the reaction's progress may be tracked over time by the absorbance of light, which indicates the concentration of A. In the "Kinetics" plot, one can see the concentration of various species and the output of the spectrophotometer over time, after the "play" or "fast forward" buttons are pressed. Lines may be added or removed using the check boxes beneath the plot, and, to determine reaction orders, the y-data may be altered using the functions next to the radio buttons, also below the plot.

If using this simulation to turn in homework:

1. Login to the vSTEM.org web site first to assure your name will be associated with your score.
2. Select the unknown you were asked to determine by clicking on the variable's symbol.
3. Perform the necessary calculations, and enter your answer into the highlighted text box below the plots (when you use scientific notation, enter, for example, 1.23e4, or 1.23e-4, not 1.23e+4 or 1.23*10^4).
4. Press the submit button (See an example in the screencast links above).
5. Remember that you must calibrate any spectrophotometer before you can take any reading. To calibrate you must set the power to the light to such a level that the spectrophotometer reads 100% transmittance when there is no dye in the cuvette.

Note that you can hit the "eject" button in the simulation controls to open up a new window containing the data from the kinetics and spectral plots. You can easily copy this data into a spreadsheet for analysis.

Alternatively, you can hit the "download" button to download a csv file you can open in excel.