A substance liberating hydroxide ions in water, an acceptor of protons, or a donor of electron pairs: each of these definitions includes the previous one. The term is thus the opposite of an acid, whatever definition of acid is used. In water, strong bases include the hydroxides of the alkali metals, while weak bases include ammonia and the amines.
You can think of bases as the chemical opposite of acids. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium ion (H3O+) concentration in water, where as bases reduce this concentration. Bases react with acids to produce water and salts (or their solutions). Some general properties of bases include:
Bitter taste (opposed to sour taste of acids and sweetness of aldehydes and ketones) Slimy, sleazy or soapy feel on fingers Caustic on organic matter, react violently with acidic or reducible substances Bases turn red litmus paper blueBase definitions
A strong base is a base which hydrolyzes completely, raising the pH of the solution towards 14. Strong bases like strong acids attack living tissue and cause serious burns. They react differently to skin than acids do so while strong acids are corrosive, we say that strong bases are caustic. Superbases are a class of especially basic compounds and harpoon bases are a special class of strong bases with poor nucleophilicity. Bases may also be weak bases such as ammonia which is used for cleaning. An alkali is a special example of a base, where in an aqueous environment, hydroxide ions are donated.
The notion of a base as a concept in chemistry was first introduced by the French chemist Guillaume François Rouelle in 1754.
Bases and pH
The pH of (impure) water is a measure of its acidity. (These numbers are correct at 23 °C and slightly different at other temperatures.)
A base accepts (removes) hydronium ions (H3O) to the solution.
Neutralization of acids
When dissolved in water, the base sodium hydroxide decomposes into hydroxide and sodium ions:
NaOH → Naand similarly, in water hydrogen chloride forms hydronium and chloride ions:
HCl + H2O → H3OWhen the two solutions are mixed, the H3O ions combine to form water molecules:
H3O → 2 H2OIf equal quantities of NaOH and HCl are dissolved, the base and the acid exactly neutralize, leaving only NaCl, effectively table salt, in solution. Acids have pH levels below 7
It is always suggested to use a weak base to neutralize any acid spills, such as soda or egg white. Neutralizing acid spills with strong bases, such as lye or ammonia, can cause a violent exothermic reaction, and the base itself can cause just as much damage as the original acid spill.
Alkalinity of non-hydroxides
Both sodium carbonate and ammonia are bases, although neither of these substances contains OH when dissolved in water:
Na2CO3 + H2O → 2 Na + OH- NH3 + H2O → NH4Strong bases
A strong base is a basic chemical compound that is able to deprotonate very weak acids in an acid-base reaction. Common examples of strong bases are the hydroxides of alkali metals and alkaline earth metals like NaOH and Ca(OH)2. Hydroxide compounds in order of strongest to weakest:
Potassium hydroxide (KOH) Barium hydroxide (Ba(OH)2) Cesium hydroxide (CsOH) Sodium hydroxide (NaOH) Strontium hydroxide (Sr(OH)2) Calcium hydroxide (Ca(OH)2) Lithium hydroxide (LiOH) Rubidium hydroxide (RbOH)The cations of these strong bases appear in the 1st and 2nd groups of the Periodic Table (Alkali and Alkali-Earth Metals).
Even stronger bases are:
Sodium hydride (NaH) Lithium diisopropylamide (LDA) (C6H14LiN) Sodium amide (NaNH2)Bases as heterogeneous catalysts
Basic substances can be used as insoluble heterogeneous catalysts for chemical reactions.
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