ELECTRODEPOSITION APPARATUS FOR STUDENT LABORATORIES PHILIP J. ELVING University of Michigan, Ann Arbor, Michigan JOHN R. HAYES Pennsylvania State College, State College, Pennsylvania M. G. MELLON Purdue University, Lafayette, Indiana T H E R E are good pedagogic reasons for including in elementary quantitative analysis at least one electrodeposition determination, generally that of copper in a copper-base alloy. I t illustrat,es a different, yet important, type of separation preliminary to gravimetric measurement; it may he conveniently used to review (or initiate) the study of the basic relationships involved in electrochemical processes; it is an excellent introduct,ion to the topic of oxidation and reduction.
ELECTRODES
has given excellent service. It is easily constructed from readily available and inexpensive components, allowing a considerable number to be made available to the class; it is quite portable so that even the most petite feminine student has no difficulty in carrying it to her laboratory desk; it operates directly from the 115-volt a.-c. line; the open wiring panel has proved very successful in demonstrating to the student the simdicitv of the eauivment and the essential nrincioles of the method. (Too frequently the less inquisitive student using a commercial piece of apparatus completes an experiment with only a very hazy idea of how the equipment functions.) To assist the student he is given a simplified schematic diagram (Figure 1). The details of construction will he apparent from the photograph (Figure 2), the construction drawing (Figure 3), and the wiring diagram ( F i r e 4). The essential electrical parts are listed, together with a sug-
ELECTRODES
One deterrent to a wider adoption of an electrodeposition determination in the elementary course has been the rather high mice of the equipment required. graduate laboratory. The simple apparatus described
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gested source and the current price. The electrical parts cost about $17 while the constructional parts are usually available in the chemistry shop or can be purchased for a few dollars. The base of the instrument is constructed of 1-inch wood, S/& plywood, and '/& hardboard (Masonite). The supporting metal framework is s/rin. brass, while the split sliding blocks which support the electrode arms and the air stirrers are of aluminum. The main panel and the side arms carrying the electrode terminals are of '/,in. Formica. It is obvious that other materials could be used. The side arms are fastened by two screws to the split block while the latter is fastened to the vertical rod by a screw passing through the split. For simplicity, stirring of solutions is accomplished by bubbling air through a capillary into the solution. The line (rubber tubing) from the compressed air outlet is divided by a glass Y-tube into two lines (rubber tubing), which lead to each capillary. An adjustable screw clamp is inserted on one or both ofethe air l i e s to the capillaries to regulate and equalize the amount of stirring in each solution. Several dozen of the assemblies have been in use in undergraduate laboratories for some years with excellent results and a minimum of maintenance. One unit is usually provided for each laboratory bench, which accommodates six students per section. By preparing the solutions beforehand, a student can readily complete a determination in duplicate during- a threehou; period. The instructions given the students for the operation of the apparatus are essentially those found in any
Wiring Diagram
Code Numbers for Fiwre. 3 and 4 '/rin. Formics. Panel 5/rin., 5-ply wood Aluminum block, / X X 1 in.. drilled to receive g l k t u b e Formica electrode side am Rubber sleeve, and tubing &mm. glass tubing, 8 in. long
Electrical Components
Quantilg Rewired
Deswi~lion
Catalogue No. LajczyelteConcord Radio Co.
Price
13N13082
0.60
Rheostat, 25-watt, 50-ohm Voltmeter, d. c., 0-8 volts Ammeter d. c., 0-3 amp. Knife swftch, SPDT Toggle switch, SPST Off-On switch plate Battery charger, 6AC4 Insulated binding posts, "4
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4 24 in.
Ehy binding post Hook up wire (two colors)
standard textbook on elementary quantitative analysis plus the following details pertaining to the use of the present apparatus: After the electrodes are in place, insert the air tube so that its tip is about '/An. above the beaker bottom. Adjust the air current to give a rapid stream of bubbles
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JOURNAL OF CHEMICAL EDUCATION
without splashing. Commence the electrolysis, adjust- When electrodeposition is complete, wash the exposed ing the resistance so that a current of 0.6 to 0.8 amp. is cathode with a stream of water from a wash bottle as the obtained a t a potential of about 2 to 3 volts (remember electrcde is being raised. As soon as the cathode is that the two solutions are connected in series). above the surface of the solution, throw the short-out To remove the electrodes, raise one set of electrodes switch and continue deposition in the other beaker for slowly from the solution, with the current left on. an additional five or ten minutes.
