Question

Cod standard method titration against sodium thiosulfate with starch indicator

Answer 1

Answer:

In the titration method for determining COD, the excess dichromate is reacted with a reducing agent, ferrous ammonium sulfate. As the ferrous ammonium sulfate (FAS) is added slowly, the excess dichromate is converted into its trivalent formStarch is now used as an indicator for the presence of iodine. ... As to why it is added near the end of the titration rather than at the beginning is because the starch-iodine complex at high I2 concentrations is relatively stable