I gain 598 MAN IS MASTERING HIS MATERIAL WORLD This reaction is typical of all displacement reactions in that it involves a transfer of electrons. Electrolysis, Which Is Cell Action in Reverse, Is Also an Oxidationreduction Reaction. When metals are plated by electrolysis, the metal goes into solution at one electrode and plates out at the other; thus, in silver-plating, a brass spoon may be used as one electrode and a bar of silver as the other electrode, the electrolyte being a solution of some silver salt. Electrons are sent to the brass spoon and are taken up by the silver ions surrounding the brass spoon to form metallic silver, which is then deposited as a plate on the spoon. of electrons J Ag"*" + electrons >- Ag" silver ions metallic silver This reaction is clearly electronization (reduction). At the other electrode electrons are removed from the silver to form silver ions. Ag" —>- Ag+ 4- electrons [loss of electrons t This reaction is de-electronization (oxidation). Electrolysis Is a Very Important Metallurgical Process. The following metals are now produced or refined by electrolysis: sodium, aluminum, magnesium, zinc, lead, copper, nickel, cadmium, bismuth, cobalt, and berylHum. Fifty years ago the price of metallic sodium was $2.00 per pound; today it is $0.14 per pound. The world production of sodium exceeds 300,000 tons per year. Sodium was formerly used to separate aluminum from its compounds, but it is now used as a reducing agent chiefly in the organic chemical industry. In 1886, 16 metric tons of aluminum were produced at a cost of about $8.00 per pound; in 1941 the Aluminum Company of America in the United States alone produced 200,000 tons of aluminum at about $0.17 per pound; this company's production in 1941, as its $200,000,000 expansion program neared completion, exceeded 300,000 tons; in 1942, 350,000 tons. In 1941 the Reynolds Metal Company was producing 50,000 tons; and the United States Government planned to build plants to produce an additional 600,000 tons of aluminum per year to meet the needs of an expanding airplane industry. The entrance of the United States into World War II considerably expanded the above production program.
ELECTRON TRANSFER 599 Magnesium is a competitor of aluminum. Magnesium is a lighter metal than aluminum, and its alloys are very strong. A new process has been developed for the production of magnesium from magnesite (magnesium carbonate), a very abundant rock, by reduction with coke in an electric furnace. This promises to make magnesium available at half the price of aluminum. Dow metal contains 90 per cent or more of magnesium, plus 10 per cent or less of aluminum, plus small amounts of other metals. Its use in airplane construction is well known. Only a few hundred pounds of cadmium were produced in 1890, but the world production in 1940 was 12,000,000 pounds. Cadmium is replacing zinc for many purposes because it produces a protective coating on iron which is superior to it under some circumstances. Electrolysis is being used increasingly in the organic chemical industry to oxidize and reduce organic compounds. The advantage of electrolytic oxidation and reduction is that it can be carried out at ordinary temperatures and pressures and can be accurately controlled. The melting-point of beryllium is 1285° C, 185° above the meltingpoint of copper. A very little beryllium added to gold makes the gold very hard. Two per cent of beryllium added to copper gives it the strength of steel, in fact, a beryllium-copper chisel may be hammered through soft steel. Two per cent of beryllium added to nickel gives it a tensile strength after heat treatment of 260,000 pounds per square inch, as compared with only 60,000 pounds per square inch for structural steel. From 0.01 to 0.02 per cent of beryllium imparts a smooth grain to copper castings and improves the electrical conductivity of copper as much as 20 per cent and at the same time makes the copper more resistant to corrosion. From 1 to 5 per cent of beryllium in silver prevents it from tarnishing with sulfur and sulfur compounds. Only those metals which are below hydrogen in the displacement series can be prepared by electrolysis of their water solutions. All metals above hydrogen in the displacement series, such as sodium, magnesium, aluminum, and beryllium, are prepared by the electrolysis of their melted compounds. A very interesting recent development is an electrolytic method of producing a high polish of mirror-like quality on steel, nickel, copper, brass, and zinc that protects them against corrosion. STUDY QUESTIONS 1. Which type of elements loses electrons most readily? 2. What are the two main types of chemical reactions? 3. Give examples of each of the four main types of electron transfer.