.
of the container in which it is nrenared. . The freshlv..n r e.~ a r e d foam usually contains unreacted isocyanate and should not he handled until it has cured several hours in a well ventilated area. The individual components are soluble in acetone and may he cleaned up easily. However, fully cured polyurethane is only slowly soluble in such solvents as dimethylformamide. It is therefore best to work with disposable surfaces. A dramatic demonstration can be performed in a 1-1tallform beaker. Mix the two components (100 ml each) and stir. If carefully supported by two glass rods, the foam can he made to form a column a t least twice the height of the beaker. Small amounts of a food coloring dye can be added to component no. 30-1961 prior to mixing with the other component. Thus, foams of different colors can he prepared. ~~~
~~~
~~
~
Figure 1.
Electrolytic-fuel cell.
'Saunders, K. J., "Organic Polymer Chemistry,'. Chapman and Hall, London, 1973, pages 318-46. 2Number 30-1961130-2023 available from Freeman Chemical Corporation, P.O. Box 247, Port Washington, Wisconsin 53074. Minimum order of $25 purchases one gallon of each component. 3Hocking,M. B., and Rayner Canham, G. W., J. CHEM. EDUC., 51, A580 (1974). 'Gilbert, G. L., private communication (1976).
The Electrolysis of Water-Fuel Submitted by: Checked by:
Cell Reactions
H. I. Feinstein a n d Vernon Gale George Mason University Fairfax, Virginia 22030 Becky J. Hickey Uniuersity of Washington Seattle, 98100
An apparatus has previously been described1 in which the polarization current of a water electrolytic cell is used to activate a flashliaht bulb. The amaratus of Humbv has now been modified that a light emitting diode or asmall electric motor may be powered by the counter emf. The counter emf in this case may also be looked upon as the product of a HZ-O2 fuel cell. Figure 1shows the complete apparatus. The binding posts labeled PROBES are used to connect the apparatus to an electrolytic cell (about 1M sulfuric acid) via carbon electrodes. The binding posts labeled MOTOR are used to connect the cell to a small toy d.c. motor. The switch labeled L.E.D. (light emitting diode)/MOTOR is used to select the load to be applied to the cell. The switch labeled CHARGEDISCHARGE is used to charge the cell or to discharge it into the load. Figure 2 is a view of the open case. Figure 3 is a schematic electronic circuit diagram. In the CHARGE nosition, enoueh hvdroeen and oxvaen will accumulate so t h a t when the D~SCHARGEposit& is selected the L.E.D. will glow or the motor armature will begin to revolve, as a function of the L.E.D./MOTOR switch position. The cycle may be repeated indefinitely. This demonstration illustrates the electrolysis of water and its reverse reaction-the H2-02 fuel cell without the added expense and inconvenience of using external sources of hydrogen and oxygen. The parts should cost no more than $10.
Figure 2 ,
view of circuit cell
CHARGE MOTOR
1 -
-~
i 3. ~schematic ~ ~electronic e circuit diagram of cell.
Parts List Suggested Sources
Jumper leads with alligator clips SPDT switches Binding posts Binding posts 1 100-ohm 'h watt resistor 1 Clip 1 LED
2 2 2 2
1 Plastic case 4" X 2 V X
'Humby, S. R., in "The Science Masters' Book, Series 1,Part 1, Physics," (Editor: Adlam, G. H. J.), John Murray, London, 1931, p. 177.
432 / Journal of Chemical Education
1W
Lafayette 99 R 00572 Lafayette 99 F 61897 Lafayette 32 F 64603 Lafayette 32 F 64611 Lafayette 52 F 2049 Lafayette 99 F 62879 Hewlett-Packard 50824655
Kelvin 133-58 1 Toy motor Edmund P-60985 1 9 V transistor radio battery 2 Carbon electrodes, beaker, acid, stand
