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Difficulty: Very hardOxidation Numbers and IUPAC Nomenclature of Redox Species

In ammonium trioxonitrate(V), NH4NO3NH_4NO_3, nitrogen exists in two distinct ionic environments. What are the respective oxidation numbers of the nitrogen atom in the cation and the nitrogen atom in the anion, and what is the systematic IUPAC name of the nitrogen-containing oxoanion formed when the anion is reduced by gaining two electrons?

  1. −3-3 and +5+5; dioxonitrate(III) ionAnswer
  2. B
    +1+1 and +5+5; trioxonitrate(III) ion
  3. C
    00 and +5+5; dioxonitrate(III) ion
  4. D
    −3-3 and +3+3; trioxonitrate(V) ion

Answer

The respective oxidation numbers are −3-3 for nitrogen in the ammonium cation and +5+5 for nitrogen in the trioxonitrate(V) anion. The reduced species formed upon gaining two electrons is the dioxonitrate(III) ion.
In the ionic compound NH4NO3NH_4NO_3, the nitrogen atom in the cation NH4+NH_4^+ has an oxidation state of −3-3 because x+4(+1)=+1x + 4(+1) = +1. The nitrogen atom in the anion NO3−NO_3^- has an oxidation state of +5+5 because y+3(−2)=−1y + 3(-2) = -1. When NO3−NO_3^- is reduced by two electrons, the oxidation number of nitrogen decreases from +5+5 to +3+3, converting NO3−NO_3^- to NO2−NO_2^-. In IUPAC nomenclature, NO2−NO_2^- is named the dioxonitrate(III) ion due to its two oxo ligands and nitrogen oxidation state of +3+3.

Step-by-Step Solution

1
Determine the oxidation state of nitrogen in the ammonium cation (NH4+NH_4^+).
Let the oxidation state of N be xx. Since hydrogen is +1+1 and the net charge is +1+1: x+4(+1)=+1  ⟹  x=−3x + 4(+1) = +1 \implies x = -3.
Ammonium is a polyatomic cation where the sum of oxidation numbers equals the net ionic charge.
2
Determine the oxidation state of nitrogen in the trioxonitrate(V) anion (NO3−NO_3^-).
Let the oxidation state of N be yy. Since oxygen is −2-2 and the net charge is −1-1: y+3(−2)=−1  ⟹  y=+5y + 3(-2) = -1 \implies y = +5.
Nitrate is a polyatomic anion where oxygen exhibits an oxidation number of −2-2.
3
Calculate the oxidation state of nitrogen after two-electron reduction of the anion and determine its IUPAC name.
Reduction by gaining 2 electrons decreases the oxidation number of nitrogen: +5−2=+3+5 - 2 = +3. The resulting species containing nitrogen in the +3+3 state with two oxygen atoms (NO2−NO_2^-) is systematically named the dioxonitrate(III) ion.
Reduction corresponds to a gain of electrons (decrease in oxidation number), and IUPAC rules for oxoanions specify the prefix for oxygen count ('dioxo-') followed by the central element and its oxidation state in Roman numerals.

Key Concept

Polyatomic Ion Oxidation Numbers and IUPAC Nomenclature of Oxoanions
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Topics

Oxidation Numbers and IUPAC Nomenclature of Redox Species

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