Bases:

             Ammonium hydroxide, or ammonia water, is very irritating to the nose and the eyes.  This substance, called a hydroxide, or a base, is often used in the home for cleaning because bases generally dissolve grease.  Milk of magnesia (magnesium hydroxide), which is used as an antacid, is a base; lye (sodium hydroxide), which is used in the manufacture of soap, is another familiar example of base.

             Bases are ionic compounds containing metal ions and hydroxide ions.  For example, sodium hydroxide contains sodium ions and hydroxide ions.   When sodium metal is placed in water, sodium hydroxide is formed and hydrogen gas is released.  Since the formula for water can be written as HOH instead of H₂O, the reaction involves single replacement:

2 Na (s)  +  2 HOH (l)   à  2 NaOH  (aq)  +  H₂ (g)

 Properties of Bases:  (in water solutions)

1.  Bases taste bitter.  A bitter taste is characteristic of all bases.  It is the presence of a base that give unflavored milk of magnesia its bitter taste.

2.  Bases feel slippery.  If you rub a drop or two of household ammonia between your fingers, you experience the slippery feeling of a base.  Wet soap is also slippery because of the presence of a base.

3.  Bases turn red litmus blue.  A common indicator, used to detect the presence of a base, is phenolphthalein which, when mixed with a base, turns pink.

4.  Bases release hydroxide ions in water solutions.  When dissolved in water, bases ionize releasing metal ions (or metallic polyatomic ions) and hydroxide ions.  For example:  when sodium hydroxide is dissolved in water, it ionizes as:

NaOH (s)  +  H₂O (l)   à   Na¹⁺ (aq)   +   OH^1- (aq)

NH₄OH  (aq)  ß -> NH₄¹⁺ (aq)  +  OH^1-  (aq)   
double arrow indicates ionization of weak base ammonium  hydroxide

 Thus bases are defined as substances that release hydroxide ions in solution.  It is these OH^1- (aq) ions that are responsible for the properties of bases.

 How Bases are Prepared:

            Bases may be prepared by the reaction of water and very reactive metals, related to the base, and by the reaction of water and certain oxides, again related to the base.

 2 K (s)  +  2 HOH (l)  à  2 KOH (aq)   +  H₂ (g)

 CaO (s)  +  HOH (l)  à   Ca(OH)₂ (aq)   plus considerable heat released

Uses of Bases:

            Ammonium hydroxide, frequently called ammonia, is used in the preparation of important related compounds such as nitric acid and ammonium chloride.  Ammonia is also used as a cleaning agent.

             Sodium hydroxide is used in the manufacture of soap, rayon, and paper.  Strong solutions of this base are very caustic; that is, they are extremely harmful to the skin.

            Calcium hydroxide, commonly known as slaked lime, is  used in the preparation of plaster and mortar.  Water solutions of calcium hydroxide, called limewater, can be used in the lab as a test for the presence of carbon dioxide.

Page Last Updated: Friday March 02, 2007           Webmaster: Larry Jones                 Pickens County School District