The COD test is based on a back titration of organic matter using ferrous ammonium sulfate (FAS) as the titrant. This statement is:

The COD test is based on a back titration of organic matter using ferrous ammonium sulfate (FAS) as the titrant. This statement is:

• A. True
• B. False
• C. It uses potassium permanganate as the oxidant
• D. It uses direct titration with FAS

Answer: (B)

In COD testing, organic matter is oxidized by an excess amount of potassium dichromate in acidic solution, and after digestion the remaining dichromate is titrated with ferrous ammonium sulfate to determine how much oxidant is left. From that, you calculate how much dichromate was used to oxidize the organics, giving the COD. The statement is not accurate because ferrous ammonium sulfate titrates the leftover oxidant, not the organic matter itself. The titration targets the oxidant (dichromate), making this a back-titration of the oxidant, not a direct titration of the organics. Also, the standard COD method uses dichromate as the oxidant, and direct titration with FAS or using permanganate as the oxidant describe different approaches.

In COD testing, organic matter is oxidized by an excess amount of potassium dichromate in acidic solution, and after digestion the remaining dichromate is titrated with ferrous ammonium sulfate to determine how much oxidant is left. From that, you calculate how much dichromate was used to oxidize the organics, giving the COD. The statement is not accurate because ferrous ammonium sulfate titrates the leftover oxidant, not the organic matter itself. The titration targets the oxidant (dichromate), making this a back-titration of the oxidant, not a direct titration of the organics. Also, the standard COD method uses dichromate as the oxidant, and direct titration with FAS or using permanganate as the oxidant describe different approaches.