For Example Engineering—Chemical, That Is

When people think of the chemical industry, they may think of the manufacturer of pesticides, pharmaceuticals, solvents, lubricants, or other relatively complex processes. Many people are surprised to learn that the vast bulk of the chemical industry revolves around the manufacture of four relatively simple chemicals sulfuric acid, phosphoric acid, sodium hydroxide, and our old friend, sodium chloride. 

The use of sulfuric acid in automobile batteries, however, does not account for its production in such vast quantities. The largest single use for sulfuric acid is fertilizers, especially a sulfuric-acid/phosphate-containing-rock mixture called superphosphate. Because phosphorus is a major mineral nutrient needed by plants and because phosphorus is a major component of bones, bone meal was once a commonly used fertilizer. Today, however, phosphate rock, treated with sulfuric acid to become more soluble, can be used, too. 

Sodium hydroxide or lye, NaOH, is used in the production of soap, textiles, petroleum products, dye, detergent, and paper. Sodium hydroxide is produced by running an electric current through a mixture of water and NaCl (table salt). The balanced equation is straightforward  

The number in front of the formula for water and also in front of the formula for table salt indicates the number of units of each that enter into the reaction. Two water molecules react with two units of sodium chloride to form one unit of sodium hydroxide, one molecule of chlorine gas, Clj, and one molecule of hydrogen gas, Hj. In other words, if we were to write each reactant individually, the reaction would be 

The tally of hydrogen before the reaction is two from each water, or four hydrogens. The total of hydrogen after the reaction is two from H2 plus one from each NaOH, or four hydrogens. Thus we have the same amount of hydrogen before and after reaction but found in different compounds. The hydrogen is balanced. The tally of oxygen before the reaction is one 

---