TOPS
--a
Dem. 779-Rates
8AI
of Rusting
To show: Steelwool rusts at different rates depending upon its cleanliness. Materials: Three 1-02. narrow neck square hottles cemented together; 5 X l'/* X 1-in. plastic tray; machine oil, HOAc, 3 tufts of fine steelwool each about 2 cms in diameter. Procedure: Wash one tuft with water, one with HOAc, and one with oil. Push into the bottom of each bottle and invert in a tray of water. Project, calling attention to equal heights of water in the three bottles. Project periodically. Observations: Water rises to bottle height with HOAc in hours, with water in days, and with oil in weeks. Dem. 780--Rate of Reaction: Zn
+ H+
Mossy zinc, granular zinc, CuCLaq, C-3.
Procedure: Project C-3 with cells two-thirds full of 1 M HCl. Add a dropperful of CuClp-aq to cell 3. Simultaneously drop granular Zn into cell 1, and an equal weight of mossy zinc into cells 2 and 3. Observations: React.ion is slowest in cell 2. I t is faster in cell 1because greater surface of zinc is exposed to the acid; it is fastest in cell 3 because of the catalytic action of Cu++. The bluish Cu++ decolorizes as red Cu coats out on the Zn.
of Reaction: Mg
+ Acids
8A1
Results by Evangeline B. Klug. To show: The effect of different acids and different acid strengths in t,he react,ion H + Mg.
+
Pvoceduve: (a) Project C-4 with cells three-fourths full of G N, 2 N, N, and N/2 HCI; simultaneously drop in 1-in. lengths of bright, clean RIg ribbon. Record times for complete reaction. (b) Repeat, using HzSOa. (c) Repeat, using HOAc. Results obtained by E. B. Klug.
GN 2N I N 0.5 N
Seconds to Complete Reaction H2S0, HOAc HCZ G 12 65 17 40 150 65 92 410 285 440 1425
Clock Reaction
8A2
To show: A clock reaction turning red, white and blue. Materials: Soh. A: 2.25 ml 37y0 HCH0/100 ml (0.3 M). Soln. B: 100 ml water to which a few drops of starch solution and tincture of iodine have been added, to give a nearly black solution. Soh. C: phenolphthalein indicator. Soh. D: thymolphthalein indicator. Soln. E : 100 ml of solution containing 1 g NaHS08 and 0.3 g iYapSOa(molarities are 0.1 NaHSOa and 0.025 M NaZSOa). Procedure: Half fill cell 1 with A, and add drops of C. Half fill cell 2 with B. Half fill cell 3 with A, and add drops of D. Project. Simultaneously dump into each cell an equal volume of E. Observations: The solutions turn red, white and blue respectively. Reaction: In cells 1and 3 OH- forms and turns the pH indicator red and blue respectively: SOa-
8A1
To show: Effect of active mass and catalyst on rate of reaction.
Dem. 7 8 I-Rate
Compiled by HUBERT N. ALYEA Princeton University Dem. 782-Patriotic
24. MISCELLANEOUS
Matevials: 1 M HCI.
Tested Overhead Projection Series
- +
+ HxO + HCHO
CH20HSOs
+ OH-
I n cell 2 the iodine is decolorized by the SOa- or HSOa-: HnO Iz + SO8- 2H+ 21SO,-
+
+
Notes 1. Formaldehyde must be present in excess, and the sulfite concentration should he low in comparison to the bisulfite. 2. Time for color change can be altered by diluting A or E. Dem. 783-Color
Clocks with HCHO
+ HS0,-
8A2
Same as preceding Dem. but substitute other pH indicators for phenolphthalein and thymolphtbalein. See Dem. 374. Dem. 784-H20, Decomposition: Effect of Temperature
8A4
To show: Increase in temperature causing increased rate of reaction. Materials: FeC1,-aq, CuClp-aq, icewater, hot water, syringe, 150 ml beaker, 3% H202. Procedure: Add drops of FeCls and CuCIa to 100 ml 3y0 H202; wait 3 min for a noticeable decomposition rate to build up. One-third fill each cell with this solution; project; call attention to the decomposition rate being the same in both cells. Now using a syringe, run hot water into one cell, and icewater into the other. Obse~~vations:The solutions are a t about 10' and 40': this makes a greater than 10-fold difference in reaction rate. Dem. 785-H,Oz
Decomposition: Surface Catalysis
8A4
Developed by Alex Leilch and David Lindenjeld, Pvinceton (1962). To show: Catalytic effect of surface on hydrogen peroxide decomposition. Volume 47, Number 6, June 1970
/
A437
Afaterials: C-2, I"eCla-aq, 3% HzO2, unglazed porcelain chips. Procedure: Project C-2 two-thirds full of H202to which sufficient drops of FeCL-aq have been added to give gentle evolution of O1. Drop bits of unglazed porcelain into cell 2. Obsevvations: Dramatic evolut,ion of O2 occurs a t the surface of the chips. Dem. 786Viscosily and Tomperdure
8A5
flxperiment adapted from Rogers, D. E., Chemistry, May, 1967, pg. 59. To show: Viscosity, analogous t o rate of chemical reaction, follows an exponential relationship with temperature. Materials: Prell liquid shampoo a t room temperature, and a t about 90°C; cell C-4, BB-shot, 0-100' thermometer, grease pencil. Procedure: Make two sharp horizontal pencil-marks in. above the base, the other 1 in. along C-4, one below the top. Fill cell 1 full, cell 2 two-thirds full, and cell 3 one-third full of Prell a t room temperature. Now pour hot Prell to fill cells2,3, and 4. Project. ( a ) Insert thermometer into cell 1, record temperature, and immediately drop in a BB-shot. Record time of passage of the shot between the t,wo marks. (b) Repeat with each cell in turn. (c) loinally return t o cell 1, now cooler, and to the others, and repeat. I n this way you will have readings a t eight different temperat,ures.
Procedure: Project C-3 with all cells half-full of 0.1 d l AgNOa. ( a ) T o each cell add 4 to 8 ml of 2 A4 NaOAc with stirring until crystals just appear. (b) T o cell 2 add 3 A4 HNOa. ( c ) TO cell 3 add 1 M HC1. Observations: Cell 1: AgC OAc + AgOAct. Cell 2: AgOAc H + as 3 M H N 0 8 + HOAc Ag+, the crystals of AgOAc disappear. Cell 5: AgOAc H + as 1 M HCI + HOAc AgCI, the AgOAc crystals are replaced by crystals of AgC1. The strong bond between H + and OAc-, forming the weak acid HOAc, yields different products in Cells 2 and 3.
+
+
+
+
Dem. 788-Shifting
+
Equilibrium
8C2
Developed by Jackman, Alyea, AicG'owan and Yarian. To show: Shifting equilibrium by changing concentration. Materials: Saturated NaCI-aq, conc. HCI, C-2, stirrer. Proceduve: Three-quarters fill C-2 cells with sat. NaC1aq. Project. Add HCl dropwise. Observations: Crystals form and settle down through the solution, as equilibrium is shifted by the common ion effect. Dem. 789-Solubilily
Producl: Ag-sohs
8C3
Developed by Jaclcman, Alyea, McGowa71 and Yarian. To show: Precipitation occurs when the product of the ion concentrations exceeds the solubility product. A.iaterials: 0.01 MAgN03, 0.01 M Na2S01, 0.01 M NaC1; test tubes, C-3, 6-2.
Obseivations: Just as a chemical reaction has a n energy barrier (energy of activat,ion, E 3 , so also viscous flow has a n energy barrier (E,:.) which must be surmounted to permit flow. A plot of the logarithm of velocity versus l/Temperature will yield a straight line, just as with chemical reaction rate, viz.
Procedure: Project four tubes immersed in water (for clarit,y) in C-2. T o tubes 1 and 2 in cell 1 add 20 drops of 0.01 M NaCl 2 drops of 0.01 A4 AgNOa. To tubes 3 and 4 in cell 2, add 20 drops 0.01 A4 Nai3Oa 2 drops 0.01 M AgNOl. Shakc all tubes well and let stand.
Where C includes constant factors and errors, and E,,, can be cnlculatcd from the slope of the line, just as is done for cncrgy of activation in a chcmical reaction.
Observations: (Two tubes each to confirm results). I n cell 1 precipitation occurs because [Ag+][Cl-] = [0.009][0.009] = 8 X which is >1.4 X the S.P.A.C,.I n cell 2 precipitation does not occur because [Ag+]2[S04=]= [0.009]2[0.009] = 7 X lo-' which is
