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Homework Help: What are some experimental errors associated with spectrophotommetry?

  1. Nov 3, 2011 #1
    This isn't an actual calculation homework problem I'm having but rather a lab discussion.

    I'm trying to find experimental errors of the experiment where you determine an equilibrium constant using spectrophotometry.

    The reaction is: Fe 3+ + SCN - = FeSCN 2+

    we used Fe(NO3)3 - iron (3) nitrate to supply Fe 3+
    and KSCN - potassium thiocyanate to supply the SCN-

    So in the final solution there would be some KNO3 i assume, and excess K+.

    The only thing I can think of is possibly that, having those other ions in the solution when measuring absorbance of FeSCN2+ will affect the reading because those other ions ...reflect light? So far I tried looking and it came up often that KNO3 as K+ ion are clear and colourless so that means they reflect all light right?

    So the spectrophotometer is set at 447 nm, where FeSCN2+ is sensitive to absorb.

    So would what I said above be a reasonable source of error? I just thought that having ions that will reflect the 447 nm wavelength will affect the absorbance reading.

    Are there other sources of errors and improvements one can make to this lab experiment?
  2. jcsd
  3. Nov 3, 2011 #2
    Well did you blank the spec before using it to make a reading? Cause that could cause some issues. I blank it before every reading.
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