NAME: _________________________________ STUDENT NUMBER____________
Quiz 4
Chem 2410
November 8, 2007
Answer all the questions below in the space provided. Show all work, otherwise a zero mark
will be given. Use the back of the page if required. Total: 10 marks. You have 15 minutes.
In a Volhard titration one back titrates excess Ag+ added to solution with SCN-, in the presence
of Fe 3+. Given that the Ksp for the AgSCN salt is 1.1*10-12, and the formation constant for the
Fe(SCN)2+ complex, 1 is 140.
a) Write out all the relevant chemical equations at the end point along with their corresponding
equilibrium expressions. Ignore Kw and any acid base chemistry. (4 marks)
b) Write down the charge balance equation. (2mark)
c) Given that the mass balance equation is:
[Ag+] =[SCN-] total = [SCN-] + [Fe(SCN)2+]
Derive an expression for the [Fe(SCN)2+] at the end point in terms, Ksp, 1 and [Fe3+].
(Hint: Do not use the charge balance equation) (6 marks)