edited by
GEORGE L. GILBERT Denison University Granville. Ohio 43023
Flashy Solutions Submitted by: Checked by:
J o h n T. Riley Western Kentucky University Bowling Green, 42101 Gregory Tennyson Denison University Granville, Ohio
Whenever I discuss topics concerning acids, bases, and acid-base indicators, I have found that some short demonstrations using a universal indicator, and other combinations of indicators, is very helpful in getting the full attention of the students and leaving them with a better understanding of these tonics. The demonstrations are as follows. ~ i r s tb.1 , M HCI is added dropwise to a solution containing 3 ml of universal indicator and three drops of 1M NaOH in 500 ml of H 2 0 to illustrate the color changes that occur a t different o H ranees. While the HCl is heinaadded, listing the p 1 1 ranges that give the I~lu~~-gnwi,green, yrll~~w. oritngc and MI col~rrsofthe indirator. th(: volumeof the solution, and the solutions so that the class can molarity of the HCI and N ~ O H calculate the number of drops of HCI needed to bring about a color change generates quite a hit of interest. Next, I let the hydrolysis of t-hutyl chloride produce the HCI needed to bring about a gradual change in the colors of a solution containing acid-base indicators. This is done by adding 1ml of t-hutyl chloride to 500 ml of 50% isopropyl alcohol-water containing 4 ml of universal indicator and 3 drops of 1 M NaOH and the solution stirred vigorously for a few seconds. A color change from blue-green to green to yellow to orange to red takes place over a period of about two minutes. Adding a few drops of 1 M NaOH neutralizes the HCl produced and the color cycling can be observed again as more t-hutyl chloride hydrolyzes. This can he repeated many times wine the same solution. third demonstration using 500 ml of 50% isopropyl alcohol-water solution containing 4 ml of universal indicator, 4 drops of 1M NaOH and 0.5 ml of t-hutyl bromide really opens the students'eyes. The t-hutyl bromide hydrolyzes so rapidly that the whole series of colors is flashed before them in a matter of 10-15 see. The most fascinating change occurs from green to yellow to orange to red which takes only 2 sec. Adding approximatelv 1 ml of 1M NaOH neutralizes the acid prod k e d and the cycle of colors can he observed again as more t-butyl bromide hydrolyzes. This can also he repeated several times until the hydrolysis reaction approaches completion. Combinations of other indicators in isopropyl alcohol-water solutions nroduce some interestine effects with t-butvl chloride and t:butyl bromide. One succcombination is O.O~% each of methvl red. methvl hlue and hromthvmol . vellow.. thvmol " hlue in ethanol. Three milliliters of this indicator solution in 500 ml of 50% isopropyl alcohol-water flashes from green to yellow to orange-red. Use the indicator with t-hutyl chloride and vou have "the turning of leaves in autumn." or with t hut;] bromide and you have a "stoplight."
Display of Sodium as a Shiny Metal Submitted by:
Cheched by:
Scott Davidson, Computer Center University of Louisville Louisville, 40208 George Wollaston Clarion State College Clarion, Pennsylvania 16214
Chunks of sodium metal as small as 0.25 cm diameter may be displayed as shiny under kerosene by adding a few drops of a high molecular weight secondary alcohol such as diisohutyl carhinol. A 1/2-02 vial with press-on plastic cap makes a suitable, safe container. After adding the alcohol, the vial should he covered loosely-e.g., with clinging plastic wrapfor a day or two while hydrogen bubbles are visible. After capping, the vial should be ventedoccasionally for a few more days or until there is no residual pressure evident. The display is good for a t least three months, with the alkoxide in solution apparently serving to react with oxygen faster then the .. metal. The usual precautions for handling sodium apply. The vial should he stored in an unconfined area away from open flames and water, preferably in a beaker to reduce the danger of an accidental spill. During the first few days after capping, the user should also he alert to the possibility of a cap pop-off and protect the eyes and face by wearing safety glasses and handling a t arm's length.
Chemical Equilibrium Submitted by: B a r b a r a A. B u r k e El Camino College via Torrance, California 90506 Checked by: Paul T. Ruda Cleueland Hills Schools Cheektowoga, N. Y. 14225 This demonstration has been designed specifically far use on an overhead projector. It is based on the following equilihrium: CuS04r,,1+ 4 KBr,,,, = K d C u B r d ~+ KZSOII.QI blue colorless green colorless
Materials Three 100-ml beakers, three 400-ml beakers, three stirring rods, graduated cylinder, overhead projector, hot plate (or bunsen burner with ring stand), ice bath, CuSOc5H20, KBr, Na2S04.10H20. Volume 54, Number 1. January 1977 / 29
Preparations Prior to Demonstration 1) 0.17 M CuS04 2) Saturated solutions of KBr, N&Op 3) Place 150 ml of the CuS04 in each of three 400-ml beakers. 4) Place two 50-ml KBr solutions and one 50-ml NaBO4 solution in three separate, labeled, 100-ml beakers.
an equilibrium situation has been set up according to theabove equation.) To the reference beaker of CuS04add 50 ml H20, to account for dilution. 3) With stirring, add 50ml ofNarSO8 solution tooneof thegreen solutions prepared in (2). The color of the solution changes back to blue indicating the equilibrium (shown above1 has been shifted to the left. Aeain add 50 ml more of water to the other -~~ " beakers to account for dilution. 4) Remove the blue solution re pared in (3) from the overhead projector and heat. As soon as the solution gets-hot the color changes to green, indicating the equilibrium has been shifted to the right. DO NOT place the beaker directly on the overhead projector, rather hold the beaker about an inch above it. The reference solution of Kz[CuBu] should also be shown. 51 Finnllv. "lace the hot solution in an ice bath to cool. Show that ~~
Demonstration 1) Show the CuSOnsolution on the overhead projector. Keep one CuSOi solution in one of the 400-ml beakers as a reference for dilutions. 2) With stirring, add 50 ml KBr solution to each of the other CuS04 solutions.' The color of the solutions changes from blue to green, showing the formation of Kz[CuBrrl. (It can be pointed out that
30 / Journal of Chemical Education
