COD as mg O 2/L = (A-B) x M x 8000/mL sample A: mL Mohr salt used for blank B: mL Mohr salt used for sample M: molarity of Mohr salt • The main reaction involved in the determination of COD is: Ag 2SO 4 Cr 2O 7 2-+ 14H+ + 6e-2Cr3+ + 7H 2O reaction: Cr