3. Geochemistry

Magnesium, Mg, is the lightest structural metal in common use. It is obtained from sea water. Lime, CaO, is added to sea water to precipitate magnesium hydroxide, Mg(OH)2. Magnesium hydroxide is then filtered and neutralized with hydrochloric acid. After evaporation of the water, the resulting MgCl2 is melted and electrolyzed to give magnesium metal.

After recovery from coal and petroleum or even sulfur mines, sulfur is converted to sulfuric acid in four steps: (1) the sulfur is burned in air to sulfur dioxide, SO2; (2) sulfur dioxide is passed over a hot platinum surface where it is converted to sulfur trioxide, SO3; (3) sulfur trioxide is passed into sulfuric acid where pyrosulfuric acid, H2S2O7, is formed, and (4) the latter is diluted with water to give sulfuric acid, H2SO4. Sulfuric acid is the number one chemical substance in terms of total mass produced by U.S. industry.

Sodium hydroxide is prepared by electrolysis of a concentrated aqueous sodium chloride solution.

To the Contemporary World

1. Drugs

Lidocaine and novocaine are bases that are used by the medical profession as anesthetics. Because of their limited solubility in water (the typical injection solvent), the basic amino group in these molecules is converted to their hydrochloride salt form which is water-soluble. Furthermore, as bases these drugs would cause localized changes in pH at the injection site. Thus, the use of salt solutions minimizes this localized irritation.

Antacids are basic compounds that decrease the amount of hydrochloric acid in the stomach. Examples are milk of magnesia (magnesium hydroxide), Mg(OH)2, and Rolaids(TM) (sodium dihydroxy aluminum carbonate, NaAl(OH)2CO3). Sodium bicarbonate (baking soda), NaHCO3, is the antacid in Alka Seltzer(TM). When Alka Seltzer(TM) is placed in water, bicarbonate ions react with hydronium ions from the acid producing the familiar fizz and belch:

Acids and bases are used in cooking. Baking soda is sodium bicarbonate, NaHCO3. Baking powder is a mixture of sodium bicarbonate, NaHCO3, and an acid salt, potassium hydrogen tartrate, KHC4H4O6. When bread bakes, these ingredients react to produce carbon dioxide and steam which expands and produces an airy loaf.

Vinegar (acetic acid, HC2H3O2) is a component of salad dressings. Citric acid is a component of fruit juices. Salts of acids (sodium benzoate and sodium propionate) are food additives that preserve foods from microorganisms.

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