Which toxic chemical is used in the COD test?

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Multiple Choice

Which toxic chemical is used in the COD test?

Explanation:
The COD test relies on a strong oxidizing agent to quantify how much organic material is present by how much oxidant is consumed. The oxidant used is potassium dichromate in concentrated sulfuric acid, and the amount of Cr(VI) reduced to Cr(III) provides a measure of the chemical oxygen demand. This reagent is toxic because it contains hexavalent chromium, a hazardous substance. Mercuric sulfate is added as a catalyst to speed up the oxidation and to help overcome interference from chloride in some samples, but it is not the primary oxidant that defines the COD test. The other options—sodium hypochlorite and chlorine gas—are used for disinfection, not for COD determination. So the toxic chemical fundamentally used in the COD test is potassium dichromate.

The COD test relies on a strong oxidizing agent to quantify how much organic material is present by how much oxidant is consumed. The oxidant used is potassium dichromate in concentrated sulfuric acid, and the amount of Cr(VI) reduced to Cr(III) provides a measure of the chemical oxygen demand. This reagent is toxic because it contains hexavalent chromium, a hazardous substance.

Mercuric sulfate is added as a catalyst to speed up the oxidation and to help overcome interference from chloride in some samples, but it is not the primary oxidant that defines the COD test. The other options—sodium hypochlorite and chlorine gas—are used for disinfection, not for COD determination. So the toxic chemical fundamentally used in the COD test is potassium dichromate.

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