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GEORGEL. GILBERT Denison University Granville. Ohio 43023
Viscosity Races
Pipet # I Pipet #2 Pipet #3 Pipet #4 Pipet #5 Pipet #6
S U B M ~BYE D Willlam M. Hemmerlln Kenton B. Abel Paclllc Unlon College Angwln, CA 94508
CHECKED BY
Arnold George Manrtleld Unlverslty Manslleld, PA 18933
We present a simple demonstration t h a t illustrates t h e correlation between molecular size and viscosity. Several alkanes and alcohols are needed (see below) t h a t are readily available and inexpensive. Equipment Needed Double-buret clamps, 25-mL pipets, ring stands, 125-mL Erlenmeyer flasks, pipet filler bulbs, stop watches. Pipets should he selected to he as identical as possible. (We use pipets that were shipped in the same box.) Each pipet was filled with water and the drain time noted. Only pipets with drain times within a 0.2-s range were selected for use in the demonstration. Chemlcals Needed Methanol, ethanol, 1-propanol, l-butanol, l-pentanol, bexane, heptane, octane, nonane, and decane.
33.1 33.1 33.1 33.0 32.9 32.9
This demonstration provides an interestina wav t o show differences in viscosityand allows for student a s timers. It is easy t o generate discussion after the demonstration, particulahy ;hen students can see structures and time on the chalkboard.
Demonstration Properties of Sulfur Dioxide SueumEo sv H. Brouwer Redeemer College Ancaner, ON L98 3NG BY CHECKED
Procedure The 25-mL pipets are mounted in douhle-buret clamps that are attached to ring stands. In succession several pipets are filled to the mark, and the time required to drain is noted. Students are invited to he the timers. There are usually quite a few students witb digital watches that have a stop watch mode. For each run five or six students are asked to submit their time. The values are written on the board, evaluated for precision, (a "Q-test" may be used to delete extraneous data), and the average time calculated. Names, times, and structures are written on the chalkboard, and a discussion follows. Students are asked what they observe from the data and what conclusions they might draw. From the data it is clear that increasing chain length causes drain times to be longer. This can be interpreted to be the result of greater viscosity. Longer chains provide greater surface area for intermolecular attractions. The greater the intermolecular attractions, the greater the resistance to flow out of the pipet. Sample Data Compound
Time
hexane heptane octane decane
30.3 31.1 31.4 32.2 32.8
methanol ethanol 1-prapanol 1-butanol l-pentanol
31.8 34.1 36.2 38.0 40.8
nonane
In each case the time given is t h e average of a t least three runs. Standard deviation is less than 0.1 s. Below are given t h e time (s) required for each of the six pipets t o drain using water.
Davld Speckherd Loras co~iege Dubuque, 1A 52001
With the current political debate on acid rain between Canada and the ~ n i & dStates, a demonstration of some of the properties of sulfur dioxide, one of the main gases implicated in acid rain, is very timely. This very simple and biief demonstration illustrates the laboratory preparation, the odor of the gas, itsacidicnature, and itssolubility in water. A greater awareness of the detrimental effects of this gas will honefullv lead to further action bv our nolitical leaders to reduce t h e emissions of sulfur dioxide from the burning of sulfur-containing coa1,and processing of sulfide ores. Procedure To a large test tube or graduated cylinder add about 1g of sodium sulfite and a few milliliters of 6 M sulfuric acid. To demonstrate the acidity of the sulfur dioxide gas produced, insert the rinsed probeof s pH meter about halfway into the test tuhe or cylinder. The water on the glass membrane will dissolve the sulfur dioxide gas, causing the pH meter to display a low pH reading (
