Tested Overhead Projection Series Cornp~ledby HUBERT N. ALYEA
Prlnceton
6. IONIZATION, ELECTRICITY
A. Proof That Ions Exist 1. CONDUCTIVITY Icontinued) Dem. 305-Conductivity
Using a Meter
To show: Conductivity of electrolytes registered on a milliammeter. Special devices: See Figures SD-305 and alternate device SD-305a. A rheostat can be included to control the meter reading. Materials: Electrolytes such as aqueous CuC19, X2Cr20,, NaC1; non-electrolytes such as alcohols, toluene, glycerine. Cell SD-304. Procedure: Nearly fill SD-304 with distilled water. Show enormous increase in conductivity when a single drop of electrolyte solution is added to each cell. Contrast the various chemicals. Drop pinches of solids into distilled water in the cells, and test conductivity. Dem. 306-Conductivity
of HCI in Water versus in Toluene
Experiment developed by William Johnson and Paul Coeoran (Princeton '68). To show: HC1 shows apparent ionization in water but not in toluene.
Un~vers~ty
conc. HC1; add an equal amount of toluene and shake. Project. (a) Lower a Mg ribbon through the top (toluene) layer into the water layer. Then lower the bared wires of SD-304 into each layer. (b) Using the hypodermic syringe, transfer 5 ml of t,he toluene layer into cell 2, taking care not to include any of the water layer. Test as before with Mg and the conductivity wires. (e) Now add 5 ml water, stir, let stand. Again test with Mg and the conductivity wires. Observations: (a, b) There is conductivity and vigorous evolution of gas each time the Mg ent,ers the water layer (Rfg 2H+ Mg++ HI). No reaction occurs in the toluene layer, and it is non-conductive. (c) HC1 must have been present in the toluene layer, since the HC1 passed in this last experiment into the water layer, which was reactive and conductive.
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+
Dem. 307-Conductivity
+
of HCI in Wder versus in Benzene
Experiment developed by Robert Barnard. To show: Activity of HC1 in water, and its ina~t~ivity in benzene. Materials: HCl in benzene as described below; Mg ribbon, stirrer, dil. HC1. Device SD-304 with 3-in. culture tubes in the cells, or SD-305.
Procedure: Half-fill culture tube 1 of SD-304 with
Preparing HC1 in benzene: Fit a 125-ml Erlenmeyer flask with a 2-hole rubber stopper bearing a delivery tube and a thistle tube reaching to its bottom. Put 20 g solid NaCl in the flask, and add 20 ml conc. HtSO, dropwise through the thistle tube. HC1 gas is evolved; pass it into 25 ml benzene for several minutcs (it becomes cloudy in 30 seconds).
SD-305.
SD-305..
Materials: Cell SD-304 with 3-in. culture tubes inserted in each cell (or SD-305); Mg ribbon, conc. HC1, toluene, 5-ml syringe and hypodermic needle.
Cendudivity using o Meter and Battery
Conductivity using a Meter ond E-i
Volume 43, Number 6, June 1966
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A539
