| Base (chemistry) |
Index for Base |
Website Links For Base |
Information AboutBase (chemistry) |
|
The common definition of a base is a Chemical Compound that absorbs Hydronium ions when dissolved in Water (a proton acceptor). An '''alkali''' is a special example of a base, where in an aqueous environment, Hydroxide Ions are donated. Bases and Acid s are seen as opposites because the effect of an acid is to increase the Hydronium ion (H3O+) Concentration in water, whereas bases reduce this concentration. Arrhenius bases are water-soluble and these solutions always have a PH greater than 7. There are other more generalized and advanced Definitions Of Acids And Bases . Common bases
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 Ion s (H3O+) and Hydroxide Ions (OH−), according to the following equation: :2H2O(l) H3O+(aq) + OH-(aq) The Concentration , measured in Molarity (''M''), or the equivalent Moles per Liter , of the ions is indicated as and [OH− ; their product is the Dissociation Constant of water with and has the value 10−14 ''M''. The pH is defined as −log [H3O+]; 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 Ion s (H3O+) from the solution, or donates Hydroxide Ions (OH-) to the solution. Both actions will lower the concentration of hydronium ions, and thus raise pH. By contrast, an acid donates H3O+ 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 hydroxide ions becomes Therefore [H+ = 10−14 mol/l, and pH = −log 10−14 = 14. Characteristics of bases Bases are slightly less viscous than pure water, have a bitter taste and are soapy to the touch. They react with acids to form Salts . Neutralization of acids When dissolved in water, the base Sodium Hydroxide decomposes into hydroxide and sodium ions: : and similarly, in water Hydrogen Chloride forms hydronium and chloride ions: : When the two solutions are mixed, the H3O+ and OH− ions combine to form water molecules: : If equal quantities of NaOH and HCl are dissolved, the base and the acid exactly neutralize, leaving only NaCl, effectively 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: : : Bases as heterogeneous catalysts Basic substances can be used as Insoluble heterogeneous Catalyst s for Chemical Reaction s. Examples are metal oxides such as Magnesium Oxide , Calcium Oxide , and Barium Oxide as well as Potassium Fluoride on Alumina and some Zeolite s. A great deal of Transition Metal s make good catalysts, many of which form basic substances. Basic catalysts have been used for Hydrogenation s, the migration of Double Bond s, Meerwein-Ponndorf-Verlay Reduction , the Michael Reaction , and many other reactions. See also External links |