litmus paper

Thân thiện

A student dips a strip of litmus paper into a clear liquid.

Definition

Noun: * A chemical indicator: Litmus paper is unsized paper (paper without a filler that makes it less absorbent) that has been treated with litmus, a water-soluble mixture of dyes extracted from lichens. It is used as a simple acid-base indicator to test the pH of a solution.

Usage

Litmus paper is used by dipping a small strip into a liquid or, for dry samples, by moistening the paper with distilled water and then touching it to the substance. The paper changes color to indicate whether the substance is acidic or basic (alkaline).

Examples

Advanced Usage

• Qualitative Test: Litmus paper provides a qualitative (yes/no) result, not a precise numerical pH value. It indicates only whether a substance is acidic (turns blue paper red) or basic (turns red paper blue).
• Neutral Result: If there is no color change, the substance is neutral (pH around 7) or very close to it.

Variants and Related Words

• Litmus test (Noun - Idiomatic): A decisive test that produces a clear positive or negative result, based on the definitive color change of litmus paper.
  • Example: Support for this policy became a litmus test for political candidates.

Synonyms

• pH indicator paper
• Acid-base test strip

Related Phrases

• Turn litmus paper red: To cause a color change indicating acidity.
  • Example: Vinegar will turn litmus paper red.
• Turn litmus paper blue: To cause a color change indicating alkalinity/basicity.
  • Example: A baking soda solution will turn litmus paper blue.

Học thuật

Noun

1. unsized paper treated with litmus for use as an acid-base indicator