The Cell Potential and the Distance between Electrodes Submitted by: Paul M. Lauren, Forest Hills High School, 67-01 110th Street, Forest Hills 75, N. Y. Checked by: Doris V. Stage,' Fort Hays Kansas State College, Hays, Kans. PREPARATION
Prepare a silicic acid gel by mixing equal volumes of 1M acetic acid and sodium silicate solution (d = 1.06). The sodium silicate solution is made by dilution of commercial 40ÂBaum6 sodium silicate (d = 1.39). Provide additional 1M acetic acid, two small beakers, a strip of zinc and one of copper, galvanometer, glass scorer, wire leads, and an equal arm U tube formed from a piece of softglass tubing 6 mm or 7 mm in diameter and about 30 cm long. Each arm should be 13 cm long.
Invert the U tube so that one arm is in one beaker and the other arm in the other beaker. The beakers should be about 20 cm apart. When the electrodes are connected to the galvanometer the needle will be deflected. Gradually shorten the ion path between the beakers by breaking off successive sections of the U tube and bringing the fresh sections of gel together. Observe successive increases in cell potential. REMARKS
DEMONSTRATION
Hold the U tube upright and fill with the silicic acid solution. Let stand overnight to gel. Add 1 M acetic acid to each beaker. Insert the zinc strip into the solution in one beaker and the copper in the other one. Present address. Madison College, Hamsonburg, Va.
Have the class try to account for the observed change in cell potential using Ohm's Law: E=IXR. This demonstration illustrates the importance of the role played by ion diffusion in determining the magnitude of the emf of a primary cell. i
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1 of Chemical Education
September 1.968
The Relative Stability of Cadmium and Cobalt Chloride Complexes Submitted by: S. B. Butler, Queens College, Flushing, N. Y. 11367 Checked by: Robert Bernoff, The Pennsylvania State University, Ogontz Campus, Abington, Pa. 19001 PREPARATION
REMARKS
Provide three 250-ml flasks, hot plate, 100-ml graduate cylinder, 5 N NaCl, 5 N CdC12, 1 N CoCIa, solid sodium chloride.
The presence of complex ions in the cadmium chloride solutions is shown by comparison with a sodium chloride solution of equal chlorine content, using a complex cobalt ion as an indicator of the relative chloride ion concentration. Flask #1 will be blue; flask f2 will be pink, showing that there is insufficientchloride ion to form the cobalt complex; flask 43, after the addition of the salt (which doubles the chloride content), will be lavender colored, indicatine the canacitv " of cadmium to comnlex with chloride ion thus preventing the full development of the blue cobalt complex.
DEMONSTRATION
Place 100 ml sodium chloride solution in flask #1 and 100 ml cadmium chloride solution in flasks #2 and #3. Heat just to boiling and maintain the temperature To each flask add 3 ml cobalt chloride solution. Add 29.2 g NaCl to flask #3, continuing to heat until dissolved.
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1 o f Chemical Education
September 1968
Volume 45, Number 9, September 1968
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A691
