Acid-Base Reactions
Acids and bases are the most important class of substances that occur in nature everywhere.
Simple definitions of acid and base are:
• Acid is a substance that produces hydrogen ion (H+) or ions in solution
• Base is a substance that produces hydroxide ion (OH-) or ions in solution.
Some acids and bases occur naturally like hydrochloric acid in the stomach and ammonia gas (in
aquatic organisms and some insects, nitrogenous waste (from the breakdown of amino acids) is
excreted in the form of ammonia). Some acids and bases are also formed when oxides of
nonmetals and oxides of metals react with water. For example, when sulfur dioxide (oxide of
sulfur, a nonmetal) combines with water, it produces sulfuric acid (acid rain) according to the
following equation.
SO2(g) + H2O(l) Æ H
2SO4(aq)
When oxide of metal like calcium oxide (also known as lime or quicklime) reacts with water, it
forms a base calcium hydroxide.
CaO(s) + H2O(l) Æ Ca(OH)2(aq)
When acid and base are mixed, they neutralize each other forming water as a soluble salt. This
reaction is known neutralization reaction.
Acid + Base Æ Water + Salt
For example, when hydrochloric acid is neutralized by the sodium hydroxide, the following
neutralization reaction takes place producing water and sodium chloride as a soluble salt.
HCl(aq) + NaOH(aq) Æ H2O(l) + NaCl(aq)\\
This is the bases for designing the antacids. An antacid is any substance, generally a base, which
counteracts stomach acidity. In other words, antacids are stomach acid neutralizers.
Some examples of antacids (brand names may vary in different countries).
• Amphojel®, AlternaGEL® contain Aluminum hydroxide, Al(OH)3
• Phillips’® Milk of Magnesia contain Magnesium hydroxide, Mg(OH)2
• Maalox®, Mylanta® contain Aluminum hydroxide and Magnesium hydroxide
• Basaljel® contains Aluminum carbonate ( Al2(CO3)3 ) gel
• Alcalak®, Calcium Rich TUMS®, Quick-Eze®, Rennie®, Titralac®, Rolaids®
contain Calcium carbonate, CaCO3
• Alka-Seltzer® contains Sodium bicarbonate, NaHCO3(Bicarbonate of soda)
• Talcid® contains Hydrotalcite (Mg6Al2(CO3)(OH)16 · 4(H2O)
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