J. A. CAMPBELL Howay Mudd College Cloromont, California 9171 1
Questions Q145. A manufacturer advertises a dry cell which will keep a 1.5-V bulb brightly lit for 2 hr (using 1 A) a t 25°C. Zn2+ Mnz03 Hoir much Zn (assuming a Zn MnOz reaction occurs) will be used up. Q146. I t is not known how glucose moves through the wall of t h e first half of the small intestine where it is absorbed into the blood, but (1) the rate of transfer is very slow in t h e absence of oxygen, (2) blood is more concentrated in glucose than t h e intestinal contents. What do you deduce about possible mechanisms from these ohservations? It may be useful to learn t h a t galactose behaves very much like glucose in this transfer process, but fructose is not so transported. Q147. A vinometer consists of a short glass tube of narrow (-0.2 mm) bore with a small funnel a t the top. I t is used by adding a few drops of wine which flow into the tube, inverting the vinometer, and using its engraved scale t o read off the percentage of alcohol in the wine opposite the top of the liquid column. What property, related t o percent alcohol, determines t h e position of the top
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of the liquid? Draw a picture of the vinometer and show the probable orientation of a 0-20% alcohol scale. Why does a vinometer work well only on low sugar wines? Q148. Indian women polish brass pots by rubbing them with calamansi ( a citrus fruit). Suggest a t least one possihle mechanism for the polishing action. Q149. Dunbar and Flanders ("Emotion and Bodily Changes," Columbia University Press, 4th Ed., 1954, p. 166). ". . . the laws of thermodynamics have no operational meaning when applied to organisms on earth because they do not exist in a closed system." Comment.
This column consists of questions (plus possible, hut certainly. not uniquely satisfactory, answers) requiring no more than a concurrent first-year, college level course, a data handbook, and a willingness to apply fundamental chemical ideas to the systems which surround us (or even are inside us). Contributions for possible inclusion are solicited. Initiated in the January 1972 issue of this Journal.
Answers A145.
1 ampere x 2 hr x 60 (min/hr) X 60 (sec/min) = 7200 amp sec = 7200eoulombs.
7200 coulombs/[96,500 (eoulombs/mole of charge) X 2 (eharges/male of Zn)] = 3.7 X moles of Zn used up 3.7 x 10W2 moles of Zn x 65.32 (g/mole Zn) = 2.4 g Zn used UP. A146.
H + O H
I
H-C-OH
I c=o I
glucose fits into a transfer molecule which is then activated by an oxidative process to carry the sugar through the intestinal wall, release it on the blood side, then return for another molecule of sugar. A147. The vinometer probably works using the surface tension of the wine; alcohol lowers surface tension (especially in the lower concentration ranges) and the liquid thread penetrates further downward into the funnel (region of increasing area of air-liquid surface). At higher concentrations the surface saturates with sugar and little change in surface tension occurs as concentration varies. A148. Corrosion of brass is primarily due to formation of Cu and Zn oxides and basic carbonates fmm the action of atmos~hericO9 and CO. on the metals. Citrus fruits contain orample:
HA-OH HA-OH HA-OH I
H glucose
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H galactose
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H f~ctase
The structures of glucose, galactose, and fructose are given. Note the similarities between glucose and galactose (both aldehydes) and their differences from fructose (a ketone). All are six carbon sugars of similar size and polarity. The facts that (1) the rate of transfer depends on [021, (2) blood is more concentrated in glucose than the intestinal contents, and (3) elueose and "ealaetose are similar but differ from fructose in transfer, all suggest active pumping by some structure and mechanism requiring O2 oxidation, not just by diffusion. The 458 I Journal of Chemical Education
CuQ,, + ZH+,,,,+ 4X-,,,, = CuX,';,, t H,O,,, A149. Some of the laws of thermodynamics apply only to isolated systems (AS maximum), some only to closed systems (AG minimum at constant T and P ) , but some are at least ~ a r t i a l applicable l~ to open (including steady state) systems. Even in open systems the zeroth law applies as does the statement that net heat flow occurs from higher to lower T. Almost every heat engine operates an an open system and thermodynamics is very useful in understanding them. It is essential to note the nature of any system of interest, hut, once that is done, thermodynamics can often he useful (and relevant) regardless of the nature of the system. For example. the Nobel prize in 1968 was given to Lars Onsager for his work on irreversiblethermodynamics.
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