edited by
J. DUDLEY HERRON Purdue Unlvemty West Latayene, lndlana 47907
Pre-Vacation Experiment: The Effect of Temperature and Torsion on the Structure of a Saccharide
I Linda K a y F o r d
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~ ' C i n c i n n a t i0h;o , Having tried with much success the Christmas Exneriment P " described in this Journal,' I developed my own Otion" experiment. The Students look forward to this sumrise Nexperimknt with a great deal of enthusiasm. In the experiment the students prepare a delicious salt-water taffy. I feel this experiment has two advantages over its predeAcessor, the peanut brittle experiment. I t is cheaper to run. It R costs appc,:r.imately thirty dollars for 125 two-person teams. y Secondly, h e students can produce a more individual product since they itave the choice of different flavorings and col-
re-vaca-
S Orkbe es:wiuent can he done in a 60-min period. If your C classes 0 7 r h w t e r , the ingredients can he measured the day H before a c 8;uied overnight. Cleanliness is very important. All lab benc: :s and equipment must he scruhbed with hot 'soapy water. After the preparation the glassware must be 0 thoroughly scrubbed. If traces of sugar are left in the beaker, L scorching will occur when the beaker is reused. Finally, during the heating, the formation of crystals on the sides of the beaker must he prevented. I had the students tape a folded paper C towel to a stirring rod. They could then dip this in water and H wipe the crystals away. E The students received the following lab sheet. No common names were given; they are provided here for the reader's Mconvenience. I'm sure the experiment can be adapted to your I own situation.
S The Enect of Temperature and Torslon on the Structure of a T Saccharide R Materials: 600-ml beaker; stirring rod; Bunsen burner; ring stand;
wire gauze; heaker tongs; graduated cylinder;thermometer (cooking); Al-foil oan Reagents: Sucrose (table sugar);3 M glucose solution (clear corn syrup);sodium chloride;hydrogenated vegetable oil (margarine);f d wlaring-red, blue, green, or yellow; flavoring-4-hydroxy-3-methoxybenzaldehyde (vanilla), 3-p-menthanol (peppermint), isoamyl acetate (banana), methyl salicylate (wintergreen),glyeyrrhizic acid (licorice),hesperidin (lemon) Procedure: Make the measurements of the first four reagents in a clean graduated cylinder. Place in your 600-ml beaker 110 ml of sucrose, 1 ml of NaCI, 74 ml of glucose solution, and 47.5 ml of water. Thoroughly mix with your stirring rod. Place over a gentle flame until all the sucrose has dissolved, stirring constantly. Increase the heat and do not stir during the rest of the heating. Wash the sides of the beaker with a rod covered with a folded paper towel, using an upward motion. This will prevent the formation of crystals. When the solution begins to boil, insert the thermometer. Heat until the thermometer registers 265*F. While you are heating, prepare an Al-foil pan and generouslylubricate with hydrogenated vegetable ail. Also obtain about 314-em slice of the vegetable oil for later. As soon as the beaker reaches 265'F, remove the heat, add the slice of hydrogenated vegetable oil and stir very gently. Pour the mixture 550 1 Journal of ChernicalEducation
onto the Al-foil pan. Take approximately 2 ml of your favorite flavoring and 3 drops of your desired color and sprinkle them across the mixture. Do not attempt to mix these last two reagents in. These will be mixed in as you pull the mixture. Let the mixture cool about 5 minutes. Meanwhile lubricate "our hands with the weetable oil. When the mixture is cool enoueh to handle, hegin t,, p& and fold, pull and fold. When the mixture takes on n F o r m shren, pull otf blte-sile pieces and wrap in saran urap. Consume the product. ~
S Sycamore High School
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'Adams, Richard C., J. CHEM. EDUC., 49,536 (1972).
An Aid to Teaching Weak Acids and Bases David E.B. Kennedy University of British Columbia Vancouuer, B.C. For those students who have not learned formal ooerational thought, a fmt year chemistry instructor still requir& as many s u r r o ~ a t concrete e props' . . as possible for abstract conceot. A general observation on first year non-science majors (many of whom canstill only think in concrete terms) is thedifficultv these students havein comparing numbers outside the ran&
-i tninn .-
A simple but extremely effective teaching expedient for solutions of equilihrium problems is merely to draw the quantities concerned roughly to scale; thus a-weak acid becomes:
[HA]- .i +
1-
and a typical 0.1 M weak base buffer after adding a few millimoles of strong base becomes:
[NH,OH+
[OH-] + r4JHJ
T h e other possibilities for other equilibrium become ohvious. Thia simple device has enabled a remarkable number of frustrated chemistry students to see where " x is small" how a n equilibrium and a buffer work, which quantities to cancel and which to ignore and even to solve buffer problems which are not "type" problems.
' Herron, J. D., J. CHEM. EDUC. 52,147 (1975).
