inject any water into the bottle until you are ready to per- form the demonstration. Students expect the hottle to "bulge" when the syringe is pressed, since you are adding material to an already "full" hottle. Hold the hottle upside down with the syringe at the bottom. Press the syringe. The hottle will collapse immedi- ately as the ammonia dissolves into the water, creating a lower Dressure inside. The deeree of collaose. of course. de- pendLon several factors, iniluding the amount of water iniected and the concentration of ammonia in the bottle. If a feadrops of phenolphthalein is added to the water, the basic pink can be seen in the hottle. Caution should be used in handling the concentrated ammonia solution. Proper eye protection should be worn and good ventilation used in the preparation. Any of the concentrated ammonia solution that comes in contact with the skin should he washed off as quickly as possible. The excess ammonia solution should be flushed down the drain. With reasonable care, this demonstration poses no great hazards. Redox Demonstrations and Descriptive Chemistry: Part 3. Copper(l1-Copper(l1) Equilibria SUBM~ED BY: Charles E. Ophardt Elmhurn College Elmhurn, IL 60126 CHECKED BY: George Wollaslon Clarion unlverslty Clarlon, PA 16214 The descriptive chemistries of copper(1) and copper(I1) ions are compared hy observing some rather unusual redox properties involving precipitation and complex ion reac- tions. The redox principles have been explained and illus- trated in two previous demonstrations.l~2 Safety Prepare the solutions containing ammonium hydroxide and ethylenediamine in a ventilated hood. 1 L 0.01 M copper(I1) chloride 500mL 0.1 M potassium iodide 500 mL 6 M ammonium hydroxide 15mL cone. ammonium hydroxide 250 mL 25% ethylenediamine 20 g potassium chloride 20 g copper thin wire turnings 600mL 0.01 M copper(1)chloride (see below) 1OOmL 0.01 M diamminecopper(1)complex (see below) Preparation of Coppefll) Chloride Dissolve 60 g ammonium chloride in 600 mL distilled water, and boil to expel oxygen. When cool, add 5-10 g copper wire turnings, and dissolve 0.6 g of capper(1) chloride with a minimum of stirring. (It may not all dissolve.) Preparation of Diamminecoppertl) Complex Do this in o hood. Into a 125 Erlenmeyer flask, put 100mL of 0.01 M copper(I1) chloride and 5-10 g thin copper turnings. Bring the solution to a boil to expel oxygen. Then add 15 mL of concentrated ammonium hydroxide, which will produce the deep blue colored copper complex (A). The solution should turn nearly colorless after about 48 h. ' Ophardt, C. J. Chern. Educ. 1987, 64, 716. 'Ophardt, C. J. Chern. Educ. 1987,64,807. Driscoll, J. A. J. Chem. Educ. 1973, 50, AS9. 248 Journal of Chemical Education Experimental Procedure Demonstrations Starting with Coppeflll) Ions Pour 200 mL of 0.01 M eopper(I1) chloride into each of four 600- mL beakers. Safety: Have watch glasses available to cover the bea- kers containing ammonium hydroxide and ethylenediamine. Procedure I. Add 100 mL of 6 M ammonium hydroxide into the first beaker to form a blue eopper(I1)complex ion (A). Proeedure2. Into the second beaker, pour 50 mL of 258ethylene- diamine to form a purple copper(I1) complex ion (B). Procedure 3. Pour 100 mL of 0.1 M potassium iodide into the third beaker, and observe the formation of a yellow solution (C) and precipitate (Dl from a redox reaction. Next add 100 mL of 6 M ammonium hydroxide, and note the rapid disappearance of the precipitate and the formation of a blue color (E). Procedure 4. Finally, dissolve about 20 g of potassium chloride into the solution in the fourth beaker and then add 5-10 g of copper turnings. Observe theslow formation of a barely visible white cloudy precipitate (F). (Go on to Proeedure 5 while waiting.) Procedure 5. (Adapted from DriscolL3) At least two days prior to the demonstration, make up the diammineeopper(1) complex (G) as indicated above to establish the equilihrium. At the time of the demonstration describe howthe flask was prepared, and refer to the color before equilibrium as the same as solution (A). At the time of the demonstration simply pour the colorless solution into a beaker, and watch the color gradually change to a deeper blue (H). . Demonstrations Starting with Coppefll) Pour 200 mL of copper(1) chloride solution with a minimum of splashing into three 600-mL beakers. Safety: Have watch glasses available to cover the beakers cantainine ammonium hvdroxide and ethvlenediamine, ~rwedure6. Into the first heakeradd 100mL of 6 M ammonium hydroxide. The resulting sdution may be slightly blue \I1 but nut as blue as the previous coppertll, solution with ammonia (A). As the solution stands for awhile, a darker blue oulw develops in the sur- fare laser due to a reaction with air. Pmcpdur~ 7. Add 5u mLof25'bethylenedian1ine to the roppertl) solutiunintherecund beaker.A purplecoloredsolution rJJ that first develops, gradually darkens, add within a few minutes produces a copper metal color on the surface of the beaker (K). Procedure 8. To the third beaker add 100 mL of 0.1 M potassium iodide solution to produce a white precipitate (L). Pour half of the solution into another beaker, and add 50 mL 6 M ammonium hy- droxide toone and 25%ethylenediamine to the other. In both cases, the precipitate dissolves to farm colored solutions, (A) and (J,K), respectively. Dlscusslon The reactions in this demonstration are designed to con- trast and compare the relative stabilities of the copper(1) and co~oer(I1) oxidation states with different anion or li- -~ -- -~ gand enGironments. It is important to note the relative order of the reduction ~otentials for the comer ions in an aoueous &. environment. Rsductlon Potentlalsa Oxidizing Agent6 [Cu(en)*12+ + e- = CUI + 8- = [Cu(NHs)2]+ + e- = [Cu(enkli + e- = [Cu(NHoh12+ + e- = CUCI + e- = cuz+ + e- = cuz+ + 2e- = O2 + 2H20 + k- = cut + e- = I, + 2s- = cu2+ + CI- + e- = cue+ + I- + e- = Reducing Agents fCu(en)P C" + 1- Cu + 2NH3 Cu + 2en [Cu(NH&l+ + 2NH3 CU + c1- C"+ C" 40H- cu 21- C"C1 cu1