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Thread: Spectrophotometric grade vs. Reagent grade

  1. #1 Spectrophotometric grade vs. Reagent grade 
    Forum Freshman
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    May 2009
    Hey there. I'm currently in a Quantitative Analytical Chemistry course at university, and my professor proposed a question for us to answer with research and labwork. In his General Chemistry course, a lab was being performed with halogens and halides, and during part of the procedure, aqueous bromine was placed in a test tube. Cyclohexane was then added to the tube, and when the color "switched" layers, the students learned about solubility in polar/non-polar solvents. However, one of his students accidentally added Spectrophotometric Grade cyclohexane rather than Reagent Grade. After vortexing, both layers became clear.

    As you can probably guess, my class' task is to try to figure out why this happened. We have some theories about impurities in the stocks and other things, but I'm thinking it has to do with the grade of cyclohexane the student used. I know that spec-grade cyclohexane absorbs light at wavelengths between 200~400 nm, but I don't know why that is. Can anybody either fill me in or link me to somewhere that might explain how the grades are different? I would really appreciate it, and I'm sure my professor would appreciate it, too :P

    PLEASE NOTE: I am in NO way asking for you to tell me the "solution" to this problem. That's obviously our job, and where all the fun is. I'm totally pumped to be testing these things with all sorts of instruments, so it would ruin the fun if somebody knew what went wrong in the student's experiment! I'm just asking for some help determining the different between the two grades. Thanks!

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  3. #2  
    JGK is offline
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    Jan 2010
    I would suggest checking the solvent suppliers website. You should be able to get certificates of analysis for each grade and do a comparison. looking for differences and how they may affect the reaction.

    "Therapy is expensive. Popping bubble wrap is cheap. You choose."
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