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organic chemistry

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Determine the percent composition of your unknown mixture.

My data for refractive indexes for acetone is 1.365 and water is 1.330. This is what my unknown mixture was composed of. How do I use this info to find percent composition of each compound?

  • organic chemistry - ,

    Draw a line with two indices, one on each end. Actually this is a graph but we can't draw pictures on these boards.
    |__________________________|

    Call the left index 0 mole fraction acetone (pure water or 1.0 mole fraction water) and right index 1.0 mole fraction acetone (pure acetone or 0 mole fraction H2O). You have an unknown mixture and you measure (I assume you've already measured it) the refractive index for it. Let's just assume the r.i. for the unknown is 1.350.
    The difference between 1.350 and the left index is 1.350-1.330 = 0.0200
    The difference between left index and right index is 1.365-1.330 = 0.03500
    So the mole fraction of the unknown is just the ratio of the part to the whole, in this case 0.0200/0.03500 = 0.5714 = 57.14 mole percent acetone.

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