Those titration in which absorbance of the solution is used to determine the end point are called photometric titrations. The method is based on the fact that the absorbance of the solution is directly proportional to concentration.
During the course of titration the concentration of the solution being titrated changes. So the absorbance of the solution changes. The end point is obtained from the graph by plotting Absorbance Vs volume of titrant added.
1. If titrand is the absorber while titrant and products do not absorb then O.D. decreases during the titration and remain constant after the end point is reached.
2. If the titrant is capable to absorb then O.D. initially remain constant but increases once the end point is reached as excess titrant is added.
3. When the products are capable to absorb the radiations while titrand and titran cannot absorb. Thus as the titrant is added to titrand the product formation take place, so the absorbance increases up to the equivalence point and after that it remain constant.
4. When the titrant and titrand are capable to absorb and the products cannot, initially absorbance decreases as titrand diminishes and after the equivalence point, again the absorbance increases due to presence of excess of titrant.
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