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A Supplement to the "Water to R o s e Demonstration SUsMlTEO BY Edwin 5. Olson
South Dakota State Un~vers~ty Brookmgs, SD 57007 CHECKED BY
Darrell D. Axtell Eastern Montana College Billings, MT 59101 Good demonstrations can focus attention on different types of scientific inquiry. Thus, we can ask and subsequently discuss why something was observed, but occasionally we might wish to explore the question of how does one actually find out what happened in a chemical reaction, Together these inquiries serve to illustrate scientific methodology, a subject which must he taught as an important part of chemical education at all levels. The demonstration described below might best he utilized in a one-year general or organic course. In the demonstration1 where the leuco form of phenosafranine reacts with Oz when shaken with air to give the pink dye, the question can be asked, "What is the product of reduction of the 02?" Superoxide, peroxide, and water might be considered. Addition of 1ml of 20% H202to the colorless leuco dye solution produces the pink color of the oxidized form of the dye, indicating that the ultimate reduction product will be water. By using the dramatic luminol reaction, the presence of peroxide or possibly superoxide can be tested in the phenosafranine dye-glucose-base system after it has been shaken several times with air. Thus, 100 ml of the rose system is poured into a beaker containing 25 ml of 0.3% luminol in 1% aqueous sodium hydroxide plus 175 ml of water plus 100 ml of 0.6% aoueous ~ o t a s s i u mferricvanide. A brief flash of chemiluminescence is observed. This may be compared with the more extensive chemiluminescence obtained using.3% hydrogen p e r o ~ i d e . ~ EDUC., 54, 366 (1977). 'Olson, E. S., J. CHEM. Fieser. L. F., and Williamson K . L., Organic Experiments. 3rd Ed., D. C. Heath, Lexington, MA, 1975, p. 258.
Blood Buffer Demonstration SUBM~TED BY Charles E. Ophardt ElrnhurSl College
HC1 and 20 ml of 0.85% lactic acid solution. The spatula used in the demonstration is a Coors 02 which holds about 0.9 g NaHCOj heaped on the spoon. Demonstrations and Remarks Note that your pH values may be slightly different, but that should not make much difference since only relative increases and decreases in pH are important at any particular step. Hydrolysis of N a H C 4
Dissolve 2.5 g NaHC03 into 100 ml of distilled water in the tall form beaker and stir at a moderate rate. Lower the electrode into the solution and measure the pH (a typical value may be 8.5). Remarks. Discuss the hydrolysis reaction of NaHC03 to explain this pH:
+
Na+ HCOf
+ HOH
-
HzC03 + Nat
+ OH-
Simulated Blood Buffer
Add 30ml of 0.1 M HCI to the sodium bicarbonate solution and note the formation of gas bubbles. Read the pH after one minute (pH is approximately 7.3). Note that the normal pH of blood serum is 7.35-7.45. Remarks. Discuss the HC1 addition as a Bronsted acid-base reaction followed by decomposition of carbonic acid to carbon dioxide. HC1+ NaHCOz H2C03
-
-
HzCOa + NaCl
C021+ Hz0
The final buffer equilibrium is represented by:
Metabolic Acidosis
Acidosis is a condition which occurs when the pH is less than normal. T o simulate this condition, add 10 ml of 0.85% lactic acid to the simulated blood buffer and read the pH after about one minute (pH is approximately 7.1-7.2). Remarks. Explain that lactic acid is produced during strenuous exercise. The pH decreases because hydrogen ion concentration increases as a result of the addition of lactic acid. Lactic acid: H(C3H403)+ H+ + C3H403This reaction is also re~resentativeof metaholic acidosis oc-
ElrnhurSt, IL 60126
CHECKED BY Paul F. Krause
University of Central Arkansas. Conway, AR 72032 Preparation This demonstration is more easily visualized by large groups if a digital pH meter with a large readout is available. However, the checker reports that the demonstration also works on a "metered" pH meter and may be suitable for small groups if a digital pH meter is not available. Standardize a digital pH meter using a pH 7 buffer solution and then set it up with a 200-ml tall form beaker on a magnetic stirrer. Weigh out 2.5 g of NaHC03 and also make available 5-10 g of NaHC03 and NH4C1solids. Prepare 50 ml of 0.1 M
three ketone bodies are acetoacetic and 3-hydroxybutanoic acids. Natural Compensation of Metabolic Acidosis
If metaholic acidosis is present, the body attempts to com~ensate(increase DH)bv increasing the rate of respiration au that morc ('0. is expired. 'l'hi, arliun uin bc sirnulatcd I,? ~r r h n ~more ('0 tn~hhlesleave the stirr~nrmurt v~ror~milv solution. Read the p ~ a f t e one r minute of vigorous stirring (pH is approximately 7.25). Remarks. Explain the slight increase in pH on the basis of equilibrium shifts in the buffer eqn. (I). A decrease in COz concentration causes the equilibrium to shift left, which decreases H+ ion concentration and thus increases the pH. Volume 60 Number 6
June 1983
493
