Base (chemistry)
A
base is a
chemical compound that will
neutralize an
acid and form a
salt + water. Bases are typically water-soluble and bitter tasting and always have a pH greater than 7 in solution. A base is able to take up a proton from an acid or able to give up an unshared pair of electrons to an acid.
Common bases
\n*baking soda\n*sodium carbonate\n*ammonia \n*Many metal oxides and hydroxides will also form basic solutions.
Bases and pH
The pH of (impure) water is a measure of its acidity. In pure water, about one in ten million molecules dissociate into hydronium ionss (H+) and hydroxyl ionss (OH−), according to the equation\n:\nThe concentration (in mole/liter) of the ions is indicated as [H+] and [OH−]; their product is the dissociation constant of water with and has the value 10−14 mole2/l2. The pH is defined as −log [H+]; thus, pure water has a pH of 7. (These numbers are correct at 23 °C and slightly different at other temperatures.)
A base accepts (removes) hydronium ionss (H+) from the solution, or donates hydroxyl ionss (OH−) to the solution. Both actions will lower the hydronium concentration, and thus raise pH. By contrast, an acid donates H+ ions to the solution or accepts OH−, thus lowering pH.
The pH of a solution can be calculated. For example, if 1 mole of sodium hydroxide (40 g) is dissolved in 1 liter of water, the concentration of hydroxyl ions becomes [OH−] = 1 mole/l. Therefore [H+] = 10−14 mol/l, and pH = −log 10−14 = 14.
Neutralization of acids
When dissolved in water, sodium hydroxide decomposes into hydroxyl and sodium ions:\n:\nand similarly, hydrochloric acid forms hydronium and chloride ions:\n:\nWhen the two solutions are mixed, the H+ and OH− ions combine to form water molecules:\n:\nIf equal amounts of NaOH and HCl (measured in moles, not grams) are dissolved, the base and the acid exactly neutralize, leaving only NaCl (table salt) in solution.
Alkalinity of non-hydroxides
Both sodium carbonate and ammonia are bases, although neither of these substances contains OH− groups. That is because both compounds accept H+ when dissolved in water:\n:\n:
Theorys of Bases
Arrhenius Bases
A compound that gives hydroxide ions in an aqueous solution
Bronsted - Lowey Base
A proton acceptor
Lewis Base
Electron pair donor
See also
\n*Acid-base reaction theories\n*Alkaline foods
\n \n \n \nnds:Base\n
Category:Chemical compounds
