Read Nitrogen's Oxidation-State Ladder Before Naming Its Oxides
Nitrogen forms a full ladder of oxides from N2O (+1) to N2O5 (+5) — knowing which oxide is the acid anhydride of which oxoacid, and which contain an N-N bond, resolves most of this cluster's questions directly.
Chemistry questions first require the material, particles or reaction condition to be identified before a formula or rule is selected.
Nitrogen oxide oxidation states and their acid anhydrides
N2O3 is the anhydride of nitrous acid (HNO2, N at +3); N2O5 is the anhydride of nitric acid (HNO3, N at +5). NO (+2) is paramagnetic (an odd-electron molecule) and does not act as a reducing agent as readily as the lower oxides; N2O5, at nitrogen's highest common oxide oxidation state, cannot be oxidised further and so cannot act as a reducing agent at all.
Which nitrogen oxides retain an N-N bond
N2O, N2O3 and N2O4 all retain a direct N-N bond in their structure; N2O5 does NOT — its structure is ionic-like, built from NO2+ and NO3- in the gas phase, with no direct N-N connection. This single fact resolves 'which oxide lacks an N-N bond' questions immediately.
Common hydride and salt preparations
NH4NO2 decomposes on heating to N2 (not NH3) — a genuine exception among ammonium salts, most of which DO release NH3 on heating (like (NH4)2SO4, (NH4)2CO3, NH4Cl). Aqueous ammonia contains mostly NH3 molecules with only a small equilibrium concentration of NH4+ and OH-, which is why it behaves as a weak base rather than fully ionising.
Industrial nitrogen chemistry: Haber and Ostwald processes
The Haber process (N2 + 3H2 ⇌ 2NH3) uses an iron-oxide catalyst (Fe2O3, often promoted with other oxides), not platinum. The Ostwald process converts NH3 to HNO3 through catalytic OXIDATION of ammonia (4NH3 + 5O2 → 4NO + 6H2O, then further oxidation and hydration) — the direction is oxidation, not reduction or hydrolysis, since nitrogen's oxidation state rises from -3 in NH3 to +5 in the final HNO3.
OlympIQ exam lens
- ✓N2O3 is the anhydride of HNO2 (nitrous acid); N2O5 is the anhydride of HNO3 (nitric acid).
- ✓N2O, N2O3, N2O4 retain a direct N-N bond; N2O5 does not.
- ✓NH4NO2 is the exception that decomposes to N2 (not NH3) on heating, unlike most other ammonium salts.
- ✓The Haber process uses an iron-oxide catalyst; the Ostwald process is an oxidation of ammonia, not a reduction or hydrolysis.
Don't assume every ammonium salt releases NH3 on heating — NH4NO2 is a genuine exception, decomposing instead to N2 and water, which is exactly the kind of exception these questions test.
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