alkali

Everyday

1. (science) An alkali is a chemical that is the opposite of an acid; it can cancel out an acid. tree →
2. (science) An alkali dissolves in water and makes a solution with a pH above 7. tree →
3. Strong alkalis, like some oven cleaners, can burn skin and eyes, just like strong acids. tree →

In the lessons

In school science the word comes with acids, pH, indicators and neutralisation: acid + alkali makes a salt and water. Litmus paper turns blue in an alkali, and universal indicator turns blue or purple. In everyday life alkalis are in soap, toothpaste, baking soda and indigestion tablets. Safety: cleaning products with alkalis carry warning signs; wear goggles and gloves. Phrases: «acids and alkalis», «a strong alkali», «a weak alkali», «alkaline batteries».

Examples

• Soap is a mild alkali, so it feels slippery. tree →
• We tested the liquids to see which were acids and which were alkalis. tree →
• Litmus paper turns blue in an alkali. tree →
• An alkali can neutralise an acid. tree →
• Indigestion tablets contain a weak alkali that calms stomach acid. tree →
• The oven cleaner is a strong alkali, so Mum wears rubber gloves. tree →
• Toothpaste is slightly alkaline. tree →
• Bicarbonate of soda makes an alkaline solution in water. tree →

Note

Plural «alkalis» (also «alkalies»); the adjective is «alkaline» (alkaline batteries, alkaline soil). Pronounced AL-ka-lie. Trap: an alkali is not «safe» just because it is not an acid; strong alkalis are dangerous too. A base is the wider word; an alkali is a base that dissolves in water. pH 7 is neutral, below 7 acid, above 7 alkali.