Acids are compounds that form hydrogen ions in solution and neutralize bases to form salt and water only. Acids may be described as either a mineral acid or an organic acid. Mineral acids, as their name suggests, are originally derived from minerals, and organic acids are originally derived from plants and animals. Examples of common organic acids are citric acid, found in citrus fruits, and ethanoic acid (vinegar). Examples of common mineral acids are hydrochloric acid and sulphuric acid. Acids may also be described as strong acids or weak acids:

A strong acid is completely ionised in aqueous solution. Example hydrogen chloride:

HCl _(aq)  →    H⁺_(aq) +   Cl^–_(aq)

A weak acid is one which is partially ionised in aqueous solution. Example carbonic acid:

H₂CO_{3 (aq)     2H⁺ (aq) + CO3^2-(aq)}

The 2 way arrow represents a 2 way reaction. H₂CO₃ ionises to form 2H⁺ + CO3^2- however 2H⁺ and CO3^2- also recombine to form H₂CO_3.

Properties if Acids

– Acids turn damp blue litmus to red

-They neutralize base to form a salt and water only, example:

HCl_(aq) + NaOH_(aq) →  NaCl_(aq) + H₂O_(l)

Acid+ base    →        salt+ water

-CO₂ is liberated from carbonates and hydrogen carbonates with effervescence, when reacted with acids,  example:

Na₂CO_3(s) + 2HCl _(aq) →   CO_{2 (g)} + H₂O _(l) + 2NaCl

-Have a sour taste

-Acids react with reactive metals to form a salt and hydrogen gas, example :

HCl _(aq) + Zn_(s) →H_{2 (g)} +ZnCl₂

-They react with sulphites to form a salt, water and sulphur dioxide, example:

K₂ SO3_(s) + 2HCl _(aq)     →      H₂O_(l) + SO_2(g) + 2KCl_(aq)