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    The Oxidation of Alcohol by Dichromate Ion

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    1) I'm given a spectrophotometer. How can I determine the rate law? I can only use the spectrophotometer to determine %T. How can I get from %T to concentration? What strategy do I have to use? Can you provide me a step by step strategy about how to get "from %T to concentration" and how to get "from concentration to rate law"?

    3) I will need to compare the class data after lab (average and Std dev) with my own data. What is standard deviation? When I'm asked to compare AVERAGE and STD DEV, what exactly do I need to write? Can you give me an example?

    4) What is the purpose of this experiment? Is it to determine the rate law?

    5) What will be my source of error? What can I do to improve it?

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    Solution Preview

    - How to determine the rate law:

    With a spectrophotometer, you cannot directly measure any rate law, but what you can measure is the concentration of a certain species under study. In this case you are going to measure the colour of chromate. You will not only be able to measure the colour, but you will be able to tell how much is present, by the intensity of the colour.

    As your reaction proceeds, you should be able to watch the concentration of dichromate disappear, such as is predicted in the chemical reaction for the oxidation of isopropanol. You should then be able to plot the concentration of the dichromate species over time, in three different ways (one is straight up[dichromate vs. time, the second is ln[dichromate] vs. time, and the third is 1/[dichromate] vs. time).

    - How to get from %T to concentration:

    The equation that you really want to use is the Beer-Lambert Law:

    A = ebC

    Which is equation (1) from your lab manual.

    But your spectrometer is giving your data in the %T form, which is not so useful, but there is an easy conversion, which is also in your lab manual (equation (2)).

    But first you need to ...

    Solution Summary

    This solution includes discussion (1000 words) and an Excel sheet set up to determine concentration from %T and the rate law from concentration when numbers are inputted.