How To Calculate Chemical Oxygen Demand

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.

Step 1

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

Step 2

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

Step 3

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

Step 4

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