Box 15.9 deals with the nitrogen cycle and the removal of nitrates and nitrites from waste water.

(a) Urea is used to reduce [NO₂]⁻ to N₂. Write a balanced equation for the reaction of HNO₂ with urea. 

(b) Sulfamic acid is also used to reduce [NO₂]⁻ to N₂ during water treatment. Give an equation for this reaction. 

(c) Nitrites can be removed using H₂O₂, [OCl]⁻ or HOCl as oxidants. How does the reduction potential for the following process depend on pH?

Suggest products for the reduction of H₂O₂ and HOCl in acidic, aqueous solution. Give equations for the reactions of H₂O₂ with [NO₂]⁻ in acidic solution, and for [OCl]⁻ with [NO₂]⁻ in alkaline solution.

Box 15.9.

Transcribed Image Text:

[NO3] (aq) + 3H+ (aq) +2e¯¯= HNO₂ (aq) +H₂O(1) E = +0.93V