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PKa of phenol lab

  1. Mar 21, 2007 #1
    1. The problem statement, all variables and given/known data

    I am working on a lab about pKa of phenol, and I don't understand how to do the following questions. Can someone please kindly help me??

    Why was the rinsing of glassware with acetone not allowed in this experiment?
    T/F Acetone has a UV absorption itself and causes errors in the absorption measurement.
    T/F Acetone would dilute the solution, thus causing errors in the measurement.
    T/F Acetone would react with the buffer and skew the pH of the solution.
    T/F Acetone will react with the phenol and cause the experiment to fail.

    The wavelength of the transition depends on the exact energy difference between either π or n orbitals and the π* orbitals -- in other words, the HOMO-LUMO gap or the n-LUMO gap. When the energy gap becomes smaller, for example by increasing the size of the conjugated system, the absorbance wavelength increases. The question is what kind of factors affect this energy gap for aromatic compounds. Please select T/F for the following options:
    T/F addition of a double bond which is conjugated to the ring will decrease the wavelength of absorbtion?
    T/F addition of electron-withdrawing substituents like keto or nitro groups will increase the wavelength of absorbtion?
    T/F addition of alkyl chains like methyl or ethyl groups will increase the wavelength of absorption?
    T/F addition of electron-donating substituents like methoxy or hydroxy groups will decrease the wavelength of absorbtion?

    3) What would cause the absorbance curves to not go through the isosbestic point?
    T/F A change in the position of the equilibrium.
    T/F A change in pH.
    T/F A change in the total concentration of phenol.
    T/F A change in the ratio of phenol to phenolate.

    Thank you !!!

    2. Relevant equations
    3. The attempt at a solution

    These are the answer I think it's right so please correct me if i got anything wrong. I have totally no idea how to do #2 if someone could kindly explain, thank you.
    #1 (T,T,F,T)

    #3 (F,F,T,F)
  2. jcsd
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