Chemical oxygen demand, or COD, is a test that measures the amount of organic compounds in water. More specifically, the test is a process of decomposing pollutants in water after two hours of boiling the water in a solution of potassium dichromate. If the COD is high, the amount of pollution in the test sample is high. The COD test involves a blank, which is a sample made by adding the reagents of acid and an oxidizing agent to distilled water. There is a formula for calculating COD.

Consider the formula for COD calculation: (a - b) X C X 8,000 / the volume of the sample in mL.

Let "a" represent the titrant used for your sample expressed in mL.

Let "b" represent the titrant used for your blank sample in mL.

Let "C" represent the normality of the ferrous ammonium sulfate. Your result will be expressed in milligrams per liter.