Some characteristics of acids: Sour in taste, turns blue litmus (an acid-base indicator) red, liberates carbon ioxide from sodium bicarbonate in aqueous solution, ionises and liberates H+ ions in aqueous solution, reacts with alkalies in an exothermic manner to form salt and water, reacts with certain metals to produce gaseous hydrogen. Some characteristics of bases: turn red litmus blue, aqueous solution is slippery to touch, produces a brilliant pink coloration with phenolphthalein (another acid-base indicator), ionises and liberates OH- ions in aqueous solution, reacts in an exothermic manner with acids to form salt and water.
Some examples of common acids are, mineral acids: HCl, H2SO4, HNO3, acids of organic origin: acetic acid or vinegar, oxalic acid, formic acid(ant stings), tartaric acid(tamarind), malic acid(apple) etc.
Some examples of bases are NaOH, Ca(OH)2, Mg(OH)2, Al(OH)3, and weak bases such as NH4OH. In addition to them, certain metal oxides viz. CaO, Na2O, MgO, Al2O3 act as bases.
Depending upon the extent of ionization in solution, both acids an bases may be termed strong or weak.