posted by :kkk: .
experiment: potentiomeric titration
1. Why is continuos stirring (use of stirrer and magnetic stir bar)important in potentiometric titration?
2. Why should the increments of addition of titrant be narrowed down as the titration approaches the equivalence point?
3. What are the advantages and disadvantages of potentiometric titration?
for 2. the reason you narrow the increments as you near the equivalence point is so you don't go over the equivalence point or at leaststay at a close range around it and don't go over by too much.
1. Should be obvious. Continuous stirring keeps the possibility of incremental hot spots (where the local concentration of the titrant is much higher than the surrounding fluid) and allows the equilibrium conditions to be approached more rapidly.
3. One advantage is that this is a method which is useful when no visual indicator is available. One disadvantage is that most potentiometric titrations require plotting the titration curve and that is so much more time consuming than using an indicator.
2. Christina's answer is ok. Another reason is that often the end point is determined by the second derivative of the titration curve. Adding exactly 0.1 mL near the end point (both before and after) is a way of getting the second derivative. That is a more accurate way of graphically determining the end point than ploying the conventional S-shaped titration curve.