John W. Hill, Dennis L. Foss and Lawrence W. Scott university of Wisconsin River Falls. WI 54022
I 1
A Copper Mirror: Electroles Plating of Copper
aqueous ammonia (0.5 M )to just dissolve the precipitate of silver oxide. Add 15 ml distilled water and mix thoroughly. If silver oxide Preparation of a silvered mirror makes an interesting lahprecipitates an dilution, add more ammonia. Now add 3 ml of 3% oratory experiment, b u t t h e cost of silver a n d its comp&nds glucose solution, mix quickly but thoroughly, and pour the mixture i s t o o expensive for most schools. W e have developed a procedure f& making a coppered mirror by e l e c t r o l e ~ s ~ ~ of l a t i ~ ~ onto the surface to be plated. Ifpossihle, swirl the container to insure deposition as evenly as possible. The solution turns yellow or brown copper o n treated glasa. T h e process does require a b o u t 2-3 assilver is deposited. Let stand about 5 min (lessifyellowingis rapid; m e of silver nitrate. b u t the c o s t of s u c h an-amount is n o t more if yellowing is slow) until a uniform coating of silver is obtained. This is a critical step in the procedure. An uneven coating or one that F o r s t u d e n t use. the exoeriment is oerformed easilv in a is too thin will lead to an uneven layer of copper. A silver coating that watch glass, P e t r i dish, o r beaker. A fla't piece of glass can he is too thick will result in a loose, flaky copper film. Now rinse the solution gently from the surface. Allow to drain dry. coooered h v m a k i n e a d a m at the edees. Careful work a n d Prepare a copper coatingsolution hy mixing, in the order given, a t k n t i o n t d d e t a i l are necessary in order to get a good mirror. ' equal volumes (about 6 or 7 ml each) of a 7%copper(lI)sulfate saluS t u d e n t s nenerallv aet a satisfactorv ( h u t n o t s ~ e c t a c u l a r ) tion, tartrate solution (prepared by adding 8 g potassium sodium m i r r o r o n t h e fir& attempt. T h e in%uctor sbohd t r y thk tartrate tetrahydrate and 2.6 g sodium hydroxide to 20 ml distilled e x p e r i m e n t before using it a s a laboratory exercise for s t u water), and 37%formalin. Mix thoroughly and pour onto thesurface dents. t o be plated. Let stand about 5 min (less if bubbles start to form on the copper surface; bubbles indicatea liftingaf thecopper film from Procedure the glass surface). Rinse the surface with distilled water and observe The glass surface to be coated must he thoroughly cleaned, prefyour rosy complexion in the copper mirror. erably with a scouring powder and hot detergent solution. Rinse Notes thoroughly with distilled water. Cover the glass surface with a 10% solution of tin(l1) chloride dihydrate. (Dissolve the tin chloride in 6 The silver r ~ l mshould be just vislhle ns n shark uf gray trr purple M hydrochloric acid and dilute tovolume. Alternatively, youmay use on the glass surface. Areas xithc,ur r h e r will not pldte well w t h a freshly prepared suspension of tin chloride; just mix the SnCI2with copper. If mzufficwnt copper is plated on the rlrsr atltrnpt, the npwater.) Let stand for about 5 mi". Rinse gently, taking care to remove plication of copper tartrate solution can he repeated. any visible particles. Allow todry; DO NOT WIPE. The tin chloride Acknowledgment treatment speeds the next step, hut an excess may contribute to poor plating. We are grateful to our colleague, Charlie Kolpin, and to the students In a small beaker, place one drop of 5%silver nitrate solution and of our Chemistry 100 course for testing the procedure for this experone drop of 10% sodium hydroxide solution. Add enough dilute iment.
752 1 Journal of Chemical Education
