Question

A common aqueous reaction in anaerobic conditions is the bacterial conversion of nitrate ions (present from biological wastes or synthetic fertilizers) to dinitrogen monoxide. This process is put to work at wastewater treatment plants, in a process called denitrification, to remove nutrients from wastewater. Unfortunately, dinitrogen monoxide is a greenhouse gas that accounts for ~10% of global anthropogenic GHG emissions. Which of the following statements is not correct?

2NO₃⁻(aq) + H₂O(l) → N₂O(g) + 2O₂(g) + 2OH⁻(aq)

A. As written above, four electrons are transferred from oxygen to nitrogen in this reaction.
B. Oxygen is oxidized.
C. Nitrogen is reduced.
D. Water can be written as a reactant in the oxidation half reaction.

Answer 1

Statement B, which claims that 'oxygen is oxidized', is the incorrect statement. Oxygen in the reaction is reduced rather than oxidized, as it ends up in molecular oxygen and hydroxide ions.

Step-by-step explanation:

In analyzing the statement given in the question regarding the anaerobic reaction of converting nitrate ions to dinitrogen monoxide, we can determine the accuracy of the statements listed:

• As written above, four electrons are transferred from oxygen to nitrogen in this reaction.
• Oxygen is oxidized.
• Nitrogen is reduced.
• Water can be written as a reactant in the oxidation half reaction.

Statement B, which asserts that oxygen is oxidized, is not accurate. In the context of this reaction, the nitrate ions (NO₃⁻) are reduced to form dinitrogen monoxide (N₂O), and oxygen atoms from nitrate are not subject to oxidation; instead, they are incorporated into molecular oxygen (O₂) and hydroxide ions (OH⁻), which means oxygen is ultimately reduced, not oxidized.

Statement D is also misleading because water (H₂O) does not directly participate in the oxidation step; it is, however, a product along with oxygen gas.

Statement A, mentioning electron transfer, does not specify whether it's accurate without additional electron accounting which would confirm the actual transfer. Statement C is accurate as nitrogen is indeed reduced during this reaction.