litmus
/'litməs/
Học thuậtThân thiện
Definition
- Noun:
- A natural dye used as a chemical indicator: Litmus is a water-soluble mixture of different dyes extracted from lichens. It is used to test whether a solution is acidic or basic (alkaline). Litmus turns red in acidic solutions and blue in basic solutions.
Usage
- Litmus is almost exclusively used in the context of chemical testing.
- It is typically used on a special absorbent paper called "litmus paper."
- The color change provides a simple, qualitative result (acidic or basic) but does not give a precise pH value.
Examples
- Noun:
- The scientist dipped the litmus paper into the liquid to determine its pH.
- A classic classroom experiment involves testing household substances with litmus.
- If the litmus turns blue, the solution is alkaline.
Advanced Usage
- "Litmus test": A figurative idiom meaning a decisive test that produces a clear "yes/no" or "pass/fail" result, often used in politics, ethics, or decision-making.
- His stance on the environmental bill became a litmus test for his political allies.
- For many voters, this issue is the litmus test for any candidate.
Variants and Related Words
- Litmus paper (noun phrase): Paper impregnated with litmus, used for testing acidity or alkalinity.
- She used a strip of litmus paper to test the water from the aquarium.
- Litmusless (adjective, rare): Not containing or not using litmus.
Synonyms
- Acid-base indicator: A more general scientific term for any substance that changes color to indicate pH.
- pH indicator: Another general term for substances like litmus, phenolphthalein, or universal indicator.
Related Phrases
- Turn litmus red/blue: A phrase describing the specific result of the test.
- Vinegar will turn litmus red because it is acidic.
Related Idioms
- "A litmus test for (something)": As described in Advanced Usage, this is the primary idiom. It compares a situation to the definitive result provided by a litmus paper test.
- The ability to work under pressure is often seen as a litmus test for this job.
Noun
- a coloring material (obtained from lichens) that turns red in acid solutions and blue in alkaline solutions; used as a very rough acid-base indicator