Acids, Bases and Salts

Definition

Acids are substances that release hydrogen ions in water and taste sour; bases (their alkalis when soluble) release hydroxide ions and taste bitter; a salt is formed when an acid reacts with a base.

Key points

• Acids turn blue litmus red; bases turn red litmus blue; the pH scale measures acidity, with 7 being neutral, below 7 acidic, and above 7 basic.
• Common acids include hydrochloric acid (in the stomach), sulphuric acid (battery and industry), nitric acid, and weak acids such as citric acid (citrus) and acetic acid (vinegar).
• Common bases include sodium hydroxide (caustic soda), calcium hydroxide (slaked lime), and ammonium hydroxide; antacids use mild bases to neutralise excess stomach acid.
• An acid and a base react to form salt and water; this is neutralisation, an exothermic reaction. Common salt (sodium chloride) comes from hydrochloric acid and sodium hydroxide.
• Everyday links: acid rain (from sulphur and nitrogen oxides) damages buildings and crops, and soil pH affects plant growth.

Why it matters for CAPF

Acid and base properties, the litmus and pH indicators, neutralisation, common laboratory acids and bases, and acid rain are recurring everyday-chemistry and environment facts.

Common confusion

All alkalis are bases (soluble in water), but not all bases are alkalis; the two terms are not identical. A strong acid is fully ionised, while a concentrated acid simply has little water, so strength and concentration are different ideas. pH below 7 is acidic, above 7 is basic, which is sometimes reversed by mistake.

Related concepts

concept ph scale, concept catalysts, concept enzymes

Parent note

chemistry everyday