In addition to demonstrating the vapor pressure of liquids this amnmtus also effectively drmoniitrates the use ot a Utuhe manometer. students in introductory chemistry courses usuallv grasp the concept of pressure reasonably amell, but the i&of Rcolumn of mercury or water representinp. a given pressure is not as readily appreciated. Thus this demonstrntion apparatus opens an excellent oppurtunity to explain pressure measured in centimeters, millimeters, or inihes of mercury (or water)
A Multicolored Luminol-Based Chemiluminescence Demonstration SueMlmo ev
John H. Chalmers, Jr.', Michael W. Bradbury, and Jill D. Fabrlcant Bloryne Corporation 1939 Richmond Avenue Houston, TX 77098
At the conclusion of the demonstration. the tuhes mav be resealed with Parafilm and stored for seveial days inarefrigerator. When needed for another demonstration the tuhes are removed from the cold to allow the DMSO t o thaw and are reshaken. Except for Rhodamine B and ruhrene, the fluors and dyes survive storage rather well; although some dark decom~ositionoroducts and a small amount of a white precipitate may accukulate, the light emission is still bright.
A Charles's Lawflapor Pressure Apparatus S U s M l m D BY
Phlllp K. Hall Unlverslty D1 Wisconsin Cenler Marshlieid, WI 54449
CHECKED BY
George Wollaston Clarion University Clarion, PA 16214
CHECKED BY
George L. Gllberl Denison University Granville, OH 43023
The luminol-DMSO-air system of Schneider2 is suitable for demonstrating chemiluminescence because of its experimental simplicity and luminous intensity. We have found that the fluorescent compounds used with oxalate esters3 work with luminol as well and mav he used to create a verv striking multicolored chemilumin&ent light show. The lu: miuol is dissolved in DMSO to a concentration of 5 me/mL. Stock solutions of the fluors and dyes may he m a d e i p in DMSO, though i t may he more convenient simply to weigh out the proper amount of the less efficient compounds such as Rhodamine B. Eosin Y, and rubrene in the test tuhes in which the demonstration w~llbe run. The demonstration is performed hv oipett~na1-3mLoftheluminol solution intoa series of smali tb medium-sized glass test tuhes and adding the fluorescent compounds t o the final concentrations indicated in the table. where a range of concentrations is listed,
An inexpensive apparatus may he constructed using two Erlenmeyer flasks and a 50-mL huret for use in lecture demonstrations to illustrate qualitatively either Charles's Law gas expansion or the vapor pressure created by liquids. As shown, the flasks fitted with two-hole rubber stoppers are connected with ruhber tubine and c l a m ~ e dto a rine stand. One flask is half filled with a ;ark solution such as hiue food colorine in water. A elass tuhe which extends to the bottom of this flask is connected with ruhber tubing to the huret tip. With the stopcock open the dark solution is poured into the huret until the connecting tubing is filled. A pinch clamp on the empty flask is then closed to prevent further movement of the solution. T o illustrate qualitatively the sensitivity of gas expansion to a mild increase in temperature, the flask containing air may he gently warmed with your hands. The solution in the buret will move up several centimeters. The flask may he heated directly with a flame to produce a more dramatic volume expansion.
Concentratlons of Fluorescent Compounds Used Color
FluwIDye
Concentration
5,12-bis(phsnyiethynyI)napMhacene FbOresCein 1.8dichlam-9.lO~is(phenylethynyl> anthracene Green 9.10-bis(phenylathyny1)anthmcene l-ehlor+9.10-bis(phenyIethynyi)anmracene 2-chlar~9.lo-bis(phenyIemynyi)anmr~~ene Salmon rubrene Rose Rhodamine B Orange Eosin Y Bluish no addiiions Red Yellow
the lower concentration gives a less saturated color and the bluish white luminol emission predominates. Light emission is initiated by adding 20 p L of saturated NaOH (in distilled H20) per milliliter of luminol solution. The tuhes are sealed with Parafilm and shaken vigorously for a few seconds or vortexed. In about a minute or so, the tuhes will begin to glow hrightly. As the glow fades, it may be restored by readmitting air and shaking the tubes.
' TOwhom correspondence should be addressed.
Schneider, H. W. J. Chem. Educ. 1970,47.519-522. Aldrichimica Acta 1983, 16(3), 59-61.
Gill, S. K.
The apparatus.
Volume 64 Number 11 November 1987
BSB
To demonstrate the pressure created bv an eva~oratine liquid the pinrh clamp-is opened, the. sol!ltion lev& in t h i 11urc.tand flask nre equalized, nnd 3 small iunount of volatile liquid is added tu the empty flnik with a medicine dropper. Upon closing the pinrh d a m p thedark solution immediately rises in the huret. I f diethvl ether is used. the buret is fillrrl in less than 1min. ~ a u t i o n s h o u l dbe observed because of the extreme flammability of diethyl ether. Acetone or methyl
970
Journal of Chemical Education
alcohol may be substituted for ether. Although they are water soluble and have significantly lower vapor pressures than ether, a 10-cm pressure change is observed after 1min. I t should be emphasized that this apparatus serves principally as a qualitative tool to demonstrate gas expansion and vapor pressure. I t is easy to set up and offers the opportunity t o provide a brief lecture demonstration of these principles without the disadvantage of using toxic mercury.
