An acid can be defined as a proton donor and has sour taste. Many acids naturally occur and have known for hundred years. Some foods contain acids, such as vinegar (ethanoic acid), citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) and ascorbic acid (vitamin C). Hydrochloric acid (HCl) occurs in the stomach to provide an acidic environment for the digestion of proteins by certain enzymes and to kill microbes. Other acids used in the laboratory include sulfuric acid, nitric acid and hydrobromic acid, which do not occur naturally and must be synthesised. These and many naturally occurring acids are manufactured extensively by the chemical industry.
Bases are also encountered in everyday life. They are used in a variety of household cleaning agents such as oven, drain and window cleaners. Common household and industrial bases include sodium hydroxide (caustic soda), sodium carbonate (soda ash), sodium carbonate-l0-water (washing soda) and ammonia. Bases such as magnesium hydroxide and aluminium hydroxide are also used in various preparations as antacids for the relief of upset stomachs and gastric reflux. Sodium hydroxide NaOH used in the manufacture of soap, some synthetic polymers and alumina; and in drain and oven cleaners. Ammonia NH3 used to make fertilisers including ammonium sulfate; in the extraction of nickel; and in household cleaners. Calcium hydroxide Ca(OH)2 used in plaster and cement. Magnesium hydroxide and aluminium hydroxide Mg(OH)2 and Al(OH)3 used in many antacid preparations.
Neutral compounds include water, common salt, and ethanol. Acetic (ethanoic) acid CH3COOH , acid In vinegar, to flavour and preserve food. Ethanol C2H5OH, neutral, alcoholic drinks and in methylated spirits. Sodium hydrogen carbonate NaHCO3, base, bicarb soda used to make cakes rise and to safely neutralise acids. Magnesium sulfate MgSO4, slightly basic, epsom salts – for constipation. Hydrochloric acid HCl, acid, cleaning cement off bricks. Maintain pool pH. Sodium hydroxide NaOH, basic, in drain cleaners.