acid

The word “acid” means in chemistry, a substance that reacts with a base, tastes sour, and can turn litmus paper red; on the pH scale it measures below 7. In plain terms, a sour or corrosive chemical substance — or, informally, the drug LSD.

“Acid” is pronounced A-sihd (/ˈæsɪd/ in IPA).

Here is “acid” used in a sentence: “Vinegar contains a mild acid called acetic acid.”

Words with a similar meaning to “acid” include acidic.

The opposite of “acid” — its antonyms — are alkaline, base and alkali.

Depending on how it is used, “acid” can be a noun and an adjective.

The word “acid” comes from Latin. From French acide, from Latin acidus, "sour," related to the verb aceo, "to be sour.".

“Acid” is a fairly common word in modern English, usually learned at around the B2 level.

Acids and bases are chemical opposites. An acid tastes sour, turns litmus paper red, and measures below 7 on the pH scale. A base, or alkali, tastes bitter, feels slippery, turns litmus blue, and measures above 7. When mixed, an acid and a base react and neutralise each other, forming a salt and water.

Everyday acids include the citric acid in lemons and oranges, acetic acid in vinegar, and lactic acid in sour milk. Your stomach uses hydrochloric acid to digest food. Industrial and laboratory acids include sulfuric, hydrochloric, and nitric acid, which are far stronger and highly corrosive. Acids range widely in strength.

The classic test is litmus paper, which an acid turns red. A pH reading below 7 also confirms it, with lower numbers meaning stronger acidity. A sour taste is another traditional sign, think lemon or vinegar, though tasting unknown chemicals is never safe. Indicators and pH meters are the reliable methods.

No. Strength matters. Strong acids like sulfuric or hydrochloric are corrosive and can burn skin, so they demand care. But weak acids are all around us and harmless in normal amounts, since the citric acid in fruit and the acetic acid in vinegar are safe to eat. Concentration and type decide the risk.