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Homework Help: Equilibirum constant

  1. Feb 6, 2008 #1
    Hey so im doing a lab write up right now for determining the value of K of the reaction of Fe3+ + SCN- <---> Fe(SCN).
    In the procedure for creating dilute solutions for analysis (by colourimetry) we mixed Fe(NO3)3 KSCN and HNO3. I know that the first two will ionize and react to form Fe(SCN) (which is a red pigment) I am however confused with the role that HNO3 plays in the emperiment.
    Thanks so much.
  2. jcsd
  3. Feb 6, 2008 #2


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    The pKa of thiocyanic acid is ~5.4. What is its pKb? How might that affect iron +3 in solution?
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