VOL.6, No. 10
T m SOLVAY PROCESS
THE SOLVAY PROCESS-A
1763
DEMONSTRATION
ARMUR HAUT, JAMES MONROE HIGH SCHOOL, NEW PORK CI~Y
In the past the writer has experienced some little difficulty in effectively teaching the "Solvay Process." This was no doubt due to the comparative complexity of the several equations necessary to bring out the process and to the fact that there was no successful demonstration to show the formation of the products. In a few laboratory manuals there are described experiments which are said to result in the precipitation of sodium bicarbonate but in these cases the action took too long and the result was far from impressive. Recently the writer undertook to study the process, making use of solid carbon dioxide. The results show that the industrial process cannot only be reproduced as a very effective demonstration but also as a successful laboratory exercise. Not only is the "Solvay Process" brought home to the student, but a large number of chemical principles may also be applied as will be shown. The directions are as follows: Concentrated ammonium hydroxide is saturated with sodium chloride, filtered, and the clear solution poured into a cylinder or graduate whose diameter is about 2 inches. The cylinder should be about half full. To this are now added pieces of solid carbon dioxide, which may be obtained from the school lunchroom or nearby stores where ice cream is sold. The carbon dioxide proceeds to neutralize the ammonium hydroxide present and a copious precipitate of sodium bicarbonate isqhrown down within ten minutes. If it is desired to completely precipitate the product, the carbon dioxide should be added until the odor of ammonia is no longer perceptible. The precipitate is then filtered and dried between filter paper. It can then be heated, at first gently, to drive off excess water and then decomposed to yield sodium carbonate and carbon dioxide. The latter is allowed to bubble through limewater and is thus identified. The sodium carbonate residue is tested with litmus to show its alkaline reaction and then tested with an acid to prove that it is really a carbonate. The filtrate contaming the ammonium chloride may be evaporated and shown to be an ammonium salt by the usual test with sodium hydroxide. The whole procedure can be easily carried out in a 45-minute period and can, if desired, very readily be done as a laboratory experiment. The following advantages of this demonstration are apparent: 1. It reproduces an important industrial process on a laboratory scale. The student has the satisfaction of making something himself. He learns by doing, and retains the idea much better. 2. The experiment also illustrates the following chemical principles and thus aids as a fine review of previous work:
(a) Decomposition of a bicarbonate. (b) Test for a carbonate. (6) Test for an ammonium salt. (d) Action of litmus on salts that are not neutral-'. e., hydrolysis. (e) The rules of solubility are admirably exemplified, namely, the insolu-
bility of the sodium bicarbonate under the conditions of the enperiment. Note here the low temperature produced hy the "dry ice" and the saturated condition of the mixture which aids the precipitation.
