acid

Everyday

1. An acid is a chemical substance that tastes sour; strong acids can burn skin and dissolve metals. tree →
2. Acid (adjective) or acidic means containing acid or tasting sour. tree →
3. Acid can describe unkind, sharp words, like an acid remark. tree →

In the lessons

In science, acids include lemon juice and vinegar (weak, safe to eat) and battery acid or hydrochloric acid (strong, dangerous). The pH scale measures acids (below 7), neutral (7) and alkalis (above 7); red cabbage water or litmus paper changes colour to show acids. Acid in the stomach helps digest food; acids from sugar harm teeth; acid rain damages trees and buildings. Safety: never touch or taste chemicals; wear goggles. Phrases: «acid rain», «citric acid», «stomach acid», «acid test» (a real test of something).

Examples

• Lemon juice is an acid. tree →
• Vinegar is a weak acid. tree →
• Acids turn blue litmus paper red. tree →
• Never touch strong acids; they can burn your skin. tree →
• Your stomach makes acid to break down food. tree →
• Sugar turns into acid that harms your teeth. tree →
• Acid rain can damage statues and trees. tree →
• Wear goggles when working with acids. tree →
• We might take him some acid drops." So they went. tree →

Note

Plural acids. Adjective: acidic. Opposite of an acid: an alkali (or base); neutral substances like pure water are neither. Not all acids are dangerous: we eat weak acids in fruit. «Sour» describes taste; «acidic» describes the chemistry.