Quick Conductivity Cell A very simple cell for indicating the relative conductivity of electrolytes, nonelectrolytes, and weak electrolytes may he constructed from readily available materials. A glass 4-dram stoppered . Nichrome (Chrome1A) wire may he used to vial ~.125 X 25 X 52 mm). .. a number 8 cork s t o.o.~ e rand construct the cell. Straightened paprrclip mre may also be used a9 clrctrodes u)test the mnducti\ity ofoll rmgents hut atrung acids. A clear plastic pill bortlc tohmmahlr f n m apharmacy, may hr used fur the cell conroiner. Of course,in the latter rase any orgnnlr solwn- wmdd ha\e to be tested tor compatihility with the container. The cork is fitted with the electrode wires by cutting two vertical slits radially opposite each other on the cork. The vertical slits in the cork allow the wires to he positioned as shown in the figure. About 1cm spacing hetween electrodes works very well with a 9-V battery. A common 9-V hatterv is the simolest source of Dower to use with the cell. A r a ~ i d rate of huhhle information indicates a strong electrolyte and a slow rate indicates a weak electrolyte. No huhhle formation indicates a nonelectrolyte solution. The observation should he made within a few seconds after touching the battery terminals directly to the cell electrodes. Although electrolysis actually occurs in the cell, the solution must be J electrically conducting in order for one to ohserve huhhle evolution. Since the wire electrodes are not inert, short observation times prevent the solution and electrodes from undergoing appreciable decomposition. Example solutions that work well with the cell are dilute aqueous Na2S04or NaHC03, dilute acetic acid, and isopropyl alcohol. Large-diameter pencil leads work well as electrodes, but these will break if not handled carefully during cell construction. Drafting supply stores sell large-diameter, long pencil leads, which are rather rugged and work very well. With the pencil lead electrodesachannel iscut out of each side of the cork toaceommodate thelarger-diameter electrodes. The pencil lead electrodes offer the advantage of electrode inertness. This work was supported hy the National Science Foundation Grant numher DPE-8470135.
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Howard P. Willlams BOX5043. Southern Station Univers!V of Southern Mississippi Haniesburg. MS 39406
Volume 62
Number 9
September 1985
799
