hydroxide ion
Very Low (Academic/Technical)Technical/Scientific
Definition
Meaning
A negatively charged ion (anion) consisting of one oxygen atom and one hydrogen atom, with the chemical formula OH⁻.
In chemistry, the hydroxide ion is the simplest oxyanion, fundamental to defining alkaline or basic solutions (high concentrations of OH⁻). It is a central species in acid-base chemistry, solubility equilibria, and many industrial and biochemical processes.
Linguistics
Semantic Notes
The term is exclusively used in chemistry and related sciences. It refers to a specific chemical entity, not a general concept. It is almost always preceded by 'the' (e.g., *the* hydroxide ion).
Dialectal Variation
British vs American Usage
Differences
No significant lexical or grammatical differences. Pronunciation differences are minor and follow general patterns of UK vs. US English.
Connotations
Identical technical connotations in both variants.
Frequency
Identical, extremely low outside of scientific contexts.
Vocabulary
Collocations
Grammar
Valency Patterns
The hydroxide ion (acts as) a nucleophile.The hydroxide ion (reacts with) an acid.A solution (contains) hydroxide ions.The (concentration) of hydroxide ions (determines) the pH.Vocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Phrases
Idioms & Phrases
- “[None - term is purely technical]”
Usage
Context Usage
Business
[No standard usage]
Academic
Essential in chemistry, biochemistry, and environmental science textbooks and research papers.
Everyday
Virtually never used in everyday conversation.
Technical
Core term in laboratory protocols, chemical engineering, water treatment, and pharmacology.
Examples
By Part of Speech
verb
British English
- The compound will hydroxide to form a precipitate.
- [No standard verb form]
American English
- The compound will hydroxide to form a precipitate.
- [No standard verb form]
adverb
British English
- [No standard adverbial form]
American English
- [No standard adverbial form]
adjective
British English
- The hydroxide-ion concentration is critical.
- A hydroxide-ion attack mechanism was proposed.
American English
- The hydroxide ion concentration is critical.
- A hydroxide ion attack mechanism was proposed.
Examples
By CEFR Level
- [Too technical for A2]
- Soap feels slippery because it makes hydroxide ions.
- The pH scale measures the concentration of hydrogen ions versus hydroxide ions in a solution.
- In the saponification reaction, the hydroxide ion acts as a nucleophile, cleaving the ester bond to yield carboxylate and alcohol.
Learning
Memory Aids
Mnemonic
Think 'HYDROgen + OXide = HYDROXIDE'. The 'ion' reminds you it's charged (OH⁻). Link it to 'high pH' – both start with 'hi'.
Conceptual Metaphor
Often conceptualised as a 'base particle' or the 'chemical opposite' of an acid (H⁺).
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Avoid translating 'ion' as 'ион' in isolation; the correct full term is 'гидроксид-ион' or 'гидроксид-анион'. Do not confuse with 'гидроксильная группа' (hydroxyl group), which is neutral and part of a molecule.
Common Mistakes
- Incorrectly saying 'hydroxide ion**s** concentration' instead of 'hydroxide ion concentration' or 'concentration of hydroxide ions'. Mispronouncing 'hydroxide' with stress on the first syllable (/ˈhaɪ.drək.saɪd/).
Practice
Quiz
What is the chemical formula for the hydroxide ion?
FAQ
Frequently Asked Questions
No. A hydroxide ion (OH⁻) is a negatively charged, free-floating species in solution. A hydroxyl group (-OH) is a neutral functional group covalently bonded within a larger molecule, like in ethanol (C₂H₅OH).
pH is a measure of hydrogen ion (H⁺) concentration. The concentration of hydroxide ions (OH⁻) is inversely related. A high concentration of OH⁻ means a low concentration of H⁺, resulting in a high pH (alkaline/basic solution).
First, find the hydrogen ion concentration: [H⁺] = 10^(-pH). Then, use the ion product of water (Kw = 1.0 x 10⁻¹⁴ at 25°C) to find [OH⁻] = Kw / [H⁺].
In common bases like sodium hydroxide (lye/oven cleaner), calcium hydroxide (limewater), magnesium hydroxide (milk of magnesia), and in all aqueous solutions where pH is above 7.