Redox and redox equilibria
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Hi, I hope you can help me. thank you.
1.What are the significant regions in a titration curve and what are the characteristics of these regions?
2.What are the differences in the Veq values obtained?
3.How is the end-point estimated using potentiometric titration if no chemical indicator is added?
4.What is the importance of continuous stirring in potentiometric titration?
5.Why should the increments of addition of titrant be narrowed down as the titration proceeds and approaches the equivalence point?
6.What are the advantages of using potentiometric titration?
7.What are the possible sources of error?
130808
Corrie writes ...
Here are some of the answers given to an earlier question about potentiometric titrations which may be useful to you:
1 & 3. Similar to pH titrations, the changes in shape of the emf vs added volume curve are used to estimate the end-point. The emf will change slowly at first, then rapidly at the equivalence point, producing a vertical, or near vertical, section of the curve. The value of the volume added at the midpoint of this region of rapid change will give a value of Veq. No visible change may occur in the solution and no chemical indicator is needed.
2. Not sure what you are asking here.
4. The importance of stirring is simple - the solution and the added titrant must be thoroughly mixed so the reactants can react completely and their concentrations are the same all over, especially on the surface of the electrode, if the emf readings obtained are to be accurate.
5. The amount of titrant added is reduced as the region of rapid emf change is approached to ensure that the readings obtained are accurate, that is all the added titrant has reacted (see stirring above) and that the equivalence point has not been 'overshot' by adding too much titrant. If the portion of titrant added is large, it will take longer before it has all reacted and the rapidly changing emf reading may not have reached a steady value. If too much is added close to the equivalence point, this could be an excess and the value of Veq from the curve will be greater than the actual value.
6. An advantages of potentiometric titrations is that they may be used to study systems that cannot be studied using conventional indicator-based titrations. Being able to record the changes during the titration continuously and electrically is also an advantage.
A disadvantage is the need for suitable electrical equipment and stable reference half-cells instead of simple titration apparatus.
7. I think the possible sources of error should be obvious from some of the answers to your questions above.
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updated: 14 August 2008
