LECTURE EXPERIMENTS IN ORGANIC CHEMISTRY
In presenting a new term to a class in chemistry, the teacher should always keep in mind the possibility that the students may memorize the definition recorded in the hook, or that given by the lecturer, without recognizing any connection between the term and the chemical behavior to which it relates. In some cases a lecture experiment may help to make the connection clear. In order that such a demonstration may be successful and carry the correct idea to the student, it must meet certain requirements. It goes without saying that the experiment must work. To insure this, every part of the apparatus should be carefully examined beforehand by the lecturer or the experiment run through before the class comes in. The apparatus should be simple, the reaction should he direct and rapid. Some definite relationship should be illustrated by the experiment, and special pains should be taken to explain this relationship in terms with which the students are already familiar, including the necessary equations, when possible. I t is believed that demonstrations similar to the ones described below will meet these requirements.
Addition and Substitution One difference between addition and substitution may readily be illustrated by showing that hromine reacts with some compounds without the evolution of hydrogen bromide, while with others that gas is liberated. In a suitable flask ( A ) of 100-150 cc. capacity, place 50 cc. of a carbon tetrachloride solution of ally1 alcohol containing about 10% of the latter, and close the flask with a two-hole rubber stopper. In one hole place a dropping funnel containing a quantity of 10% solution of bromine in carbon tetrachloride. In the other place a right angle bend of glass tubing, and connect this with a U-tube containing enough solutionjof silver nitrate to prevent the free passage of gas. Set up a second flask (B) with similar connections, but place in this one about 50 cc. of a 10% solution of phenol. This should be freshly prepared from pure crystals of phenol in order to obtain a colorless liquid. Now allow the bromine solution to drop slowly into each flask, when the red color will disappear promptly in each case. No precipitate will form in the U-tube connected with flask ( A ) , which shows that no hydrogen bromide is evolved in the reaction taking place there. Heat is liberated, consequently air will bubble through the silver nitrate solution at the beginning of the experiment. In the U-tube connected with flask (B) a precipitate of silver bromide will be formed, showing that hydrogen bromide was formed in that flask. Black cardboard behind the apparatus will make the result more easily seen at a distance. 1597
1598
JOURNAL OF CHEMICAL EDUCATION
JULY,1930
Action of Nitrous Acid on a Primary Amine Fit a 100-cc. flask with a two-hole rubber stopper and attach to one opening. a bent glass tube arranged to collect gas over water. In the other place a dropping funnel, the stem of which should extend to about the center of the bulb of the flask. In the flask place about 4 g. of ethylamine hydrochloride, 4 cc. of concentrated hydrochloric acid, and enough water to fill the flask, including the neck, to a level about 2-3 cm. below the stopper. In the dropping funnel place a solution of sodium nitrite containing 3.5 g. of the salt in 10 cc. of water. Adjust the delivery tube so as to collect gas, and in order to take care of small quantities of oxides of nitrogen that may be formed it is advisable to fill the collecting cylinder with 10% solution of sodium hydroxide. Allow the nitrite solution to enter slowly, then close the stopcock of the funnel. While the gas is being collected, arrange a condenser with a suitable receiving vessel. Test the gas with a lighted splinter. Pour one-half the liquid from the generating flask into a distilling bulb, attach to the condenser and distil 25-30 cc. Test the distillate for ethyl alcohol by means of the iodoform reaction. Write the necessary equations.
