Tested Overhead Proiection Series Compiled by
HUBERT N. ALYEA Princeton University
12. GROUP I. THE ALKALI METALS
B. The Alkali Metals. Ammonium 2. AMMONIUM ION (Continued) Dem. 436-Ammonium
Amalgam
Experiment developed by James A. Young.
(b) Upon reversing the current the wire grows thin again, bubbles appear on it; copper scuffs off of it. It is a dramatic experiment. Note : 1. A great current density is used here to hasten effect. In actual electroplating a low current density insures a tightly-attached plating. 8. I n place of Pt electrode, one can use an insulated Cu wire with 3/4 in. of very thin P t wire soldered to its free end.
To show: Formation of ammonium amalgam by electrolysis of an ammonium salt using a mercury cathode. Materials: E-1, NarSOraq, 7 mm tubing 4 in. long, G2, cotton-tipped swab, conc. HCl, filmstrip coated with colorless phenolphthalein indicator, 6 N NaOH, medicine dropper.
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Procedure: Put 5 ml Hg 20 ml (NH,)pSO.,-aq in E-1. Now lower the 7 mm tubing into the Hg. Insert Pt-coil electrodes from cell E-1 in the 7 mm tuhe and the outside solution. (a) Project. Pass 9 volts dc for 10 minutes, the electrode in the small tube being the negative pole. (b) Holding a finger over the tubing to retain its solution, transfer the solution in the small tuhe to the two cells of C-1. Project. To each add a dropperful of 6 N NaOH. Now hold the phenolpthalein-coated filmstrip in one, above the reactants, and the swab soaked with conc. HC1 in the other. Observations: (a) Bubbles are given off as ammonium amalgam forms in the 7-mm tube. (b) When NaOH is added to the ammonium amalgam in C-2, NH2forms; this turns the phenolphthalein red and produces white smoke. Reference: (1929).
Dem. 438-Fehling's
To show:
Ted
Fehling's test for a reducing sugar.
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Materials: Soln. A: NaI
