Common bases, strong and weak

Ammonia, NH3 , is a weak base. Ammonia is an ingredient in household cleaners. Ammonia has a pungent odor. The unshared pair of electrons on the "N" is attracted to H+ ions. Water and ammonia react to form ammonium ions, NH41+ , and hydroxide ions, OH1- . Here a H+ is stripped off of a water molecule.

NH3(g) + H2O(l) <---> NH41+ (aq) + OH1- (aq)


The reversible reaction has an equilibrium constant identified as Kb with a subscript "b" to indicate that the equilibrium has OH in the products side of the equation. The equilibrium constant is Kb = 1.8 x 10-5

Kb = 1.8 x 10-5

Most weak bases are organic compounds related to ammonia. These organic compounds are called amines. This class of compounds have a carbon chain in place of the hydrogen atoms that are present in ammonia. An example is methylamine, CH3NH2. The CH3- group is attached to the "N" nitrogen atom. The unshared electron pair on the ammonia can accept a H1+ from and acid. The general formula for primary amines is RNH2.

The metal oxides like CaO react with water to form hydroxides. The hydroxides like KOH or Al(OH)3 are sources of hydroxide ions in water solutions. Click here to see how aluminum hydroxide a common stomach antacid behaves in water.

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Dr. Walt Volland all rights reserved -1997-2000