blank is used to dissipate the error brought about by impurities. What is the other reason of using blank in Mohr method?

Answer 1

Using the amount of chromate ion calculated to give the best end point gives such an intense yellow color that generally less than the optimum is used; therefore, generally, one must over titrate to get the end point color. The blank helps correct for that excess AgNO3 added to reach the end point. A second reason is that some people/students have trouble seeing the end point. In fact, through my years of teaching, I found that more students had more trouble with the Mohr method than any other procedure and all of it was because of the difficulty in seeing the end point. By using a blank, this problem corrects itself somewhat.