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Acids and Bases: Salts |
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pH and Tooth DecayTeeth are made up of a soft material called dentin covered by a hard enamel layer. The outer layer is mostly hydroxyapatite (Ca10(PO4)6(OH)2), a sparingly soluble salt. Tooth decay occurs when the teeth become demineralized (or the hydroxyapatite dissolves) and cavities form. You were surely told as a child that eating sugar causes cavities. This could be true if sugar causes hydroxyapatite to be more soluble. Does sugar do this? The answer is yes and the explanation lies in plaque. Plaque is the substance that sticks to your teeth and consists mostly of bacteria. Bacteria live on energy obtained by decomposing sugars. One product of sugar decomposition is lactic acid (CH3CHOHCO2H). The more sugar that enters the mouth, the more the bacteria thrive and the more lactic acid is produced.
Ca10(PO4)6(OH)2(s)
PO43-(aq)
+ H3O+(aq) OH-(aq)
+ H3O+(aq) This removes them from the equilibrium, causing the equilibrium to shift to the right (Le Châtelier's Principle). Hence, the more sugar one eats, the more lactic acid produced. As more lactic acid is produced, the protective enamel coating becomes more soluble. As the enamel dissolves, tooth decay is very likely. There are many other insoluble salts that contain bases as anions. The addition of an acid will increase the solubility by reacting with the base. ![]()
![]() Are there any others? ![]() |
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