Question

1. The introduction states that nitrate is partially reduced to nitrite:

a) what are the chemical differences between the nitrate and nitrite

b) what was oxidized? include the chemical reactions

c) why is the time that nitrate solution and zinc power are in contact an important factor in the procedure?

Answer 1

a) The chemical differences between the nitrate and nitrite-

The nitrate ion (NO3^-) is the stable form of combined nitrogen for oxygenated systems. It is chemically unreactive. It can be reduced by microbial action. The nitrite ion (NO₂⁻) contains nitrogen in a relatively unstable oxidation state. Nitrogen in the nitrate exhibits an oxidation state of +5, while nitrogen in the nitrite ion exhibits an oxidation state of +3.

b) Nitrite ion is oxidized to nitrate when it combines with oxygen, O₂.

2NO₂^- + O₂(g) --> 2NO₃(aq)

c)

Zn(s) + NO3^- (aq)----> NO₂^- + ZnO

Zinc dust will reduce nitrate to nitrite, but will not further reduce nitrite to nitrogen gas or other nitrogenous by products when used sparingly.

Zinc is a powerful reducing agent. If there is any NO₃^- amount of zinc dust will rapidly reduce it to NO₂^-

So time factor is important in this reaction