acid number
Low (C2)Technical/Scientific
Definition
Meaning
A chemical measure (usually expressed in milligrams of potassium hydroxide) of the amount of free acid present in a substance such as a fat, oil, or wax.
A standardized laboratory value used to assess the quality, freshness, or degree of degradation in fats, oils, lubricants, and petrochemical products by quantifying their acidic components.
Linguistics
Semantic Notes
This is a highly specific term from analytical chemistry and industrial quality control. It is not used metaphorically. The related term 'acid value' is synonymous.
Dialectal Variation
British vs American Usage
Differences
No significant differences in meaning or usage. Both regions use 'acid number' and 'acid value' interchangeably in technical contexts.
Connotations
Purely technical and neutral in both dialects.
Frequency
Equally low-frequency in both technical registers.
Vocabulary
Collocations
Grammar
Valency Patterns
The acid number of [SUBSTANCE] is [VALUE].[SUBSTANCE] has an acid number of [VALUE].Vocabulary
Synonyms
Neutral
Weak
Vocabulary
Antonyms
Usage
Context Usage
Business
Used in procurement, quality assurance reports, and product specifications for oils and fats.
Academic
Used in chemistry, food science, and engineering research papers and lab reports.
Everyday
Virtually never used.
Technical
The primary context. Found in standards (e.g., ASTM, ISO), lab manuals, and quality control documentation.
Examples
By Part of Speech
verb
British English
- The lab will titrate the sample to acid-number it.
- We need to acid-number these batches of lubricant.
American English
- The technician will run tests to acid number the oil.
- The protocol requires us to acid number each sample.
adjective
British English
- The acid-number determination is crucial.
- Follow the acid-number procedure.
American English
- The acid-number test is complete.
- We reviewed the acid-number results.
Examples
By CEFR Level
- The acid number tells us about the oil's quality.
- A rising acid number in the transformer oil indicates ongoing degradation and the potential for corrosion.
- The procurement specification stipulates that the supplied coconut oil must have an acid number not exceeding 0.5 mg KOH/g.
Learning
Memory Aids
Mnemonic
Think of an ACID test giving you a NUMBER grade for how acidic a fat or oil is.
Conceptual Metaphor
DEGREE IS A NUMBER (The degree of acidity/degradation is conceptualized as a quantifiable figure).
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Do not translate as 'кислотное число' generically; in specific technical contexts, 'число омыления' (saponification number) is a different, related measure.
- Beware of false cognates: 'acid номер' is incorrect.
Common Mistakes
- Using 'acid number' to refer to pH (e.g., 'The acid number of lemon juice is 2').
- Confusing it with 'saponification number' or 'iodine value'.
- Treating it as a countable noun in plural without context (e.g., 'different acid numbers' is fine for different substances).
Practice
Quiz
What does a high acid number most directly indicate in a vegetable oil?
FAQ
Frequently Asked Questions
No. pH measures the concentration of hydrogen ions in an aqueous solution. Acid number measures the mass of potassium hydroxide required to neutralize the free acids in a non-aqueous substance like oil or fat.
A low acid number indicates a low concentration of free acids, which generally corresponds to a fresh, refined, or high-quality fat or oil that has not undergone significant hydrolysis or oxidation.
It is central to the food industry (for edible oils and fats), the biodiesel industry, the lubricants and petroleum industry, and the chemical manufacturing sector.
It is almost always expressed in milligrams of potassium hydroxide (KOH) per gram of sample (mg KOH/g).