What chemical is used to test for phosphorus in effluent?

The correct answer is Ascorbic Acid, which is used in the colorimetric method for the determination of phosphorus levels in effluent samples. This method relies on the reaction between phosphorus and molybdate ions in an acidic solution, resulting in the formation of a colored complex. Ascorbic Acid acts as a reducing agent that enhances the sensitivity of the color reaction, thereby allowing for the accurate quantification of phosphorus concentrations.

In this process, the intensity of the color produced is measured spectrophotometrically, and it correlates to the concentration of phosphorus in the sample. The use of Ascorbic Acid is favored because it provides reliable and reproducible results, making it a standard practice in wastewater analysis.

The other chemicals listed do not serve the same purpose in phosphorus testing: Sodium Bisulfite is often used for removing chlorine or other oxidative contaminants, Phosphoric Acid is not a testing reagent but rather a form of phosphorus itself, and Calcium Carbonate is primarily used to neutralize acidity or adjust pH rather than detect phosphorus.