nitrous acid
LowTechnical / Scientific
Definition
Meaning
A weak, unstable acid containing nitrogen, with the formula HNO₂.
In chemistry, it refers to a specific inorganic acid that exists primarily in cold, aqueous solution and is used as a reagent in organic synthesis, notably in the formation of diazonium salts. In atmospheric chemistry, it can refer to the gas-phase acid involved in pollution and nitrosation reactions.
Linguistics
Semantic Notes
This is a highly specialized chemical term. It is primarily used in inorganic and organic chemistry contexts. In everyday language, 'nitrous' is more commonly associated with 'nitrous oxide' (laughing gas). Do not confuse 'nitrous acid' (HNO₂) with 'nitric acid' (HNO₃).
Dialectal Variation
British vs American Usage
Differences
No significant usage differences; the term is identical in spelling and usage in scientific contexts across both variants. Pronunciation differs slightly (see IPA).
Connotations
Neutral scientific term in both variants.
Frequency
Equally rare outside of chemistry in both variants.
Vocabulary
Collocations
Grammar
Valency Patterns
NOUN + of + nitrous acidADJECTIVE + nitrous acidVERB + nitrous acidVocabulary
Synonyms
Neutral
Weak
Usage
Context Usage
Business
Virtually never used.
Academic
Used in chemistry textbooks, research papers, and laboratory manuals.
Everyday
Extremely rare; might appear in advanced educational contexts or popular science articles.
Technical
Primary context. Used in chemical engineering, atmospheric science, and laboratory procedure documentation.
Examples
By Part of Speech
adjective
British English
- The nitrous acid solution must be kept chilled.
- They studied the nitrous acid concentration.
American English
- The nitrous acid solution needs to be kept cold.
- They measured the nitrous acid concentration.
Examples
By CEFR Level
- Nitrous acid is a chemical studied in science.
- The laboratory prepared a fresh solution of nitrous acid for the experiment.
- Nitrous acid decomposes readily at room temperature.
- Diazotisation, a key step in azo dye synthesis, relies on the reaction of a primary aromatic amine with nitrous acid.
- The atmospheric formation of nitrous acid (HONO) plays a significant role in the morning hydroxyl radical budget.
Learning
Memory Aids
Mnemonic
Think 'NITRO-gen + -OUS' (less oxygen than nitric acid) + ACID. 'Nitrous' sounds like 'night' + 'rous' – imagine a weak acid that only works at night.
Conceptual Metaphor
N/A for highly technical terms.
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Do not confuse with 'азотистая кислота' (correct) and 'азотная кислота' (nitric acid, HNO₃).
- The adjective 'nitrous' is 'азотистый', not 'нитрозный' (nitroso-).
Common Mistakes
- Misspelling as 'nitrus acid'.
- Confusing it with 'nitric acid' (a much stronger, common acid).
- Pronouncing 'nitrous' as 'night-rus' instead of 'nye-trus'.
Practice
Quiz
Nitrous acid (HNO₂) is best described as:
FAQ
Frequently Asked Questions
The chemical formula is HNO₂.
No, it is unstable and readily decomposes, especially when warmed, into nitrogen oxides and water. It is typically prepared in cold, dilute aqueous solution just before use.
Its primary use is in organic chemistry for the diazotisation of primary aromatic amines, a key reaction for producing diazonium salts, which are precursors to azo dyes and other compounds.
Nitrous acid (HNO₂) is a weak, unstable acid where nitrogen has an oxidation state of +3. Nitric acid (HNO₃) is a strong, common, and stable acid where nitrogen has an oxidation state of +5.