Week of February 15, 2010

The Final Formal Scientific Report (on Experiments 12 - 15) is due next week (the week of February 22, 2010). For MS Word users, a useful list of "special character features" is available in PDF format (this includes instructions for using superscripts, subscripts, symbols, etc. in your final paper). In the discussion section of your final report, you should use a confidence limit analysis when comparing your experimental results with the theoretical results.

Bring a stopwatch or a watch with a second hand to lab this week. You need to time reactions. You may also want to bring your laptop computer. There are PC's available in lab if you don't have a laptop but there may be a wait to use them. You will be able set up spreadsheets to process and plot your data in lab. There are instructions for using Excel for calculations and a sample Excel template for experiment 16-077b in your laboratory manual.

Report Sheets for Experiment 16-077b will be due the Week of March 1, 2010.

Extra report sheets for experiment 16-077b: Files are in PDF format.

In the first part of the experiment you will determine the reaction order and the rate constant. You will set up a series of 10 reactions using varing intial concentrations of KI and K₂S₂O₈ at room temperature. Using a colorimetric assay, you will determine the rate for each of the 10 reactions. From your data you will be able to determine the rate constant and the reaction order using the general rate-law expression:

where k is the rate constant at a specific temperature, [A] and [B] are the initial molar concentration of the reactants, and a and b are empirically-determined constants (you'll determine a and b using your data from this experiment) whose sum constitutes the order of the reaction.

In the second part of the experiment you will determine the activation energy for reaction 1. The rate constant of reaction 2 varies with temperature. The Arrhenius equation describes the relationship between k and T:

where, E_a is the activation energy, T is the absolute temperature, A is a constant specific to the reaction, and R is the Ideal Gas constant. If you measure k at differernt temperatures, you can plot ln k as a function of 1/T and fit a straight line through the data points. The slope of this line corresponds to -E_a/R, thus E_a can be determined. In this part of the experiment you will measure the reaction rate at 5 different temperatures(using constant intial concentrations of KI and K₂S₂O₈ and determine k. You can then construct a graph of ln k vs 1/T to determine E_a.

An example of an Excel spreadsheet designed for experiment 16-077b is found on pages 83 - 84 of your lab manual.