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Transcript
Oxidation-Reduction Titrations
VCL 20-1: Study of Oxidation-Reduction Titrations
Titrations provide a method of quantitatively measuring the concentration of an unknown solution. This is
done by delivering a titrant of known concentration into an analyte of known volume. (The concentration
of an unknown titrant can also be determined by titration with an analyte of known concentration and
volume.) In oxidation-reduction (redox) titrations, the voltage resulting from the mixture of an oxidant
and reductant can be measured as the titration proceeds. The equivalence point of the titration, or the
point where the analyte has been completely consumed by the titrant, is identified by the point where the
voltage changes rapidly over a small volume of titrant delivered. In this assignment, you will observe this
titration curve by titrating FeCl2 with KMnO4.
1. Start Virtual ChemLab and select Study of Oxidation-Reduction Titrations from the list of
assignments. The lab will open in the Titrations laboratory.
2. The buret will be filled with KMnO4 and a solution containing FeCl2 will be in the beaker on the stir
plate. The horizontal position of the orange handle is off for the stopcock. Open the stopcock by
pulling down on the orange handle. The vertical position delivers volume the fastest with three
intermediate rates in between. Turn the stopcock to one of the fastest positions. Observe the titration
curve. When the volume reaches 45 mL double-click the stopcock to turn it off.
3. Examine the graph of voltage vs. volume (blue line) and sketch the titration curve below. Label the
axes.
4. Write a balanced net ionic equation for the reaction in acidic solution of FeCl2 and KMnO4 (Fe2+
becomes Fe3+ and MnO4- becomes Mn2+).
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Chapter 20
5. The reduction potential of Fe2+ is 0.732 volts, and the reduction potential of MnO4- in acidic solution
is 1.507 volts.
If you titrate KMnO4 into FeCl2, what happens to the voltage of the solution as the titration starts and
proceeds to the end?
168