Redox Titration

In a titration you measure the quantity of one reactant that is required to consume all of another reactant. To accomplish this you measure the volume of liquid released from the buret during the procedure. The initial level of the liquid in the buret is observed and recorded. The flask containing the sample to be titrated is placed under the buret. When the purple titrant enters the flask it reacts with the colorless sample. The products of the reaction are colorless. The titrant is a purple solution. The titrant solution in the buret is added to the sample solution in the flask. At this stage all of the added titrant has reacted within the flask. We know this because the solution in the flask has reverted back to being clear and colorless. Now we are at the end point of the titration where enough titrant has been added from the buret to react with all of the reactant in the flask and the solution's color has changed slightly due to a slight excess of titrant. At this point we can take our final reading.






Picture from left to right :
Initial reading , Placing the flask ,Adding titrant.. , ..to the sample , One final squirt








Slightly pink - the end point,Final reading.




In this animation of an oxidation/reduction titration at first we see the purple titrant reacting with the colorless sample. The products of this reaction are clear and colorless so no change takes place in the sample's appearance. When the sample is completely consumed we are at the equivalence point. When any more titrant is added the color changes slightly and we are at the end point. If any more titrant enters the flask the color darkens and we have overshot the end point.

Titrant has entered the flask,Before ,After ,The equivalence point

The end point, Overshoot.

Discussion
This redox titration provides a simple example of the principle of titration and limiting reactant. Because permanganate is intensely colored, no indicator is needed. As soon as some permanganate is left over (that is, as soon as it stops being the limiting reactant) some purple color is visible. The animation sequence is designed to illustrate this on the nanoscale (atomic/molecular scale).
The equation for the reaction is
5 H2O2(aq ) + 6 H+(aq ) + 2 MnO4-(aq ) --> 5 O2(g ) + 2 Mn2+(aq ) + 8 H2O(l )

Exam and Quiz Questions
1. Why does the intense violet color of the permanganate ion disappear when the permanganate solution is first added to the hydrogen peroxide solution?
2. Why does the color of permanganate ion remain when the last addition of permanganate solution is made to the hydrogen peroxide solution?