J. A. CAMPBELL Harvey Mudd College Claremont, California 9171 1
Questions Q193. Fast draw expert Bill Munden claims to have been "clocked a t 0.001 second for drawing a Colt 45, firing it, and jamming it back into its black leather holster." Evaluate this claim from a molecular point of view. Q194. G. D. Garlick and J. R. Dymond in "Oxygen Isotope Exchange between Volcanic Ash and Ocean Water" [Geol. Soc. Amer. Bull., 81, 2137 (1970)] report that '80 concentration in volcanic ash deposits resulting from selective exchange with surrounding ocean waters increase with time of exposure to the ocean. The exposure ages as judged both by their strata and by K-Ar dating (which agreed) range from 0.05 to 46.1 X lo6 yrs. The authors state, "It is surprising that K-Ar determinations yield reasonable ages. We expected neutral argon atoms to he far more mobile than the oxygen ions that are chemically bonded to various cations and volumetrically constitute the hulk of the glass." Comment on why this might or might not be so. Q195. Most bacteria will not grow if the p H is less than 4.5. What is the corresponding [H+]? Describe the pmduction of an acetic acid-sodium acetate buffer that would have a pH of 4.5.
Q196. The concentration of oxygen in natural bodies of water follows a daily cycle, called the oxygen pulse, maximizing about 3 P.M. and minimizing about 7 A.M. Interpret these data. Q197. According to Robert Shapiro, R. E. Semis, and M. Welcher, [J.Amer. Chem. Soc., 92.2,422 (1970)l sodium bisulfite, NaHSO3, converts cytosine to uracil to the extent of 90% in yeast RNA under physiological conditions. The reaction is reversible upon adding OH-. H S O J is the first chemical found that can specifically change one natural nucleic acid component into another. Sulfur dioxide is released in the burning of coal and other fossil fuels, and is also used as a food additive. Shapiro, et al., discuss possible relationships between these two observations. Do you see any? This column consists of questions (plus possible, but 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 A193. The claimed time sounds impossible. An object moving uniformly a t the speed of sound travels about 1 St in 0 . 0 1 sec. Nerve impulse, carried by molecular collisions, can hardly exceed the speed of sound (essentially the same as molecular velocities). Since each nerve command must travel about 5 ft (hand to brain and return) it's hard to see how any action, even a very simple one, could take less than 0.005 see. You might also like to consider the energy required to aecelerate a gun out of the holster, stop it, and return it in such a short time. Remember F = ma; E = Fd = md2/t2.0.1 second might be just possible. A194. Every natural crystal contains imperfections, many due to vacant sites in the crystal array and some due to interstitial holes in addition t o the vacant sites. Conversion of K + to Ar radioactively produces a large atom from a small ion. The large atom is probably wedged quite tightly in the crystal and rather immobilized by the surrounding oxide cage. Oxide ions are not only smaller, they are identical in size and so could move into empty sites, or even interchange, more readily than the Ar atoms. It is true that the attractive forces between cations and anions are greater than those with Ar atoms but the repulsive forces are similar and are more effective in restricting the Ar atoms, which are larger than the ions. It is the relative repulsive forces which determines the relative mobilities in the crystals. The figures cited suggest that the Ar atoms are almost completely immobilized.
[OAc-I [HOAcl -=-
K,
[H I +
3 X lo-' = -= 1.8 X
lo-"
2 (to one significant figure]
So make a solution by adding NaOAc (to give OAc-) and HOAc in the ratio of 2 to 1. For example, add 0.2 mole of solid NaOAc to 1 liter of 0.1 M HOAc. Adjust p H as closely as desired to 4.5 by adding HOAc (to lower pH) or NaOAc (to raise pH). A196. Photosynthesis requires light and varies in rate with available sunlight. In the early afternoon aqueous phatosynthesis reaches a maximum rate causing rapid increase of [Od as its rate of production maximizes. At night the 0%is used in respiration, none is regenerated, and much escapes from the surface into the atmosphere so that its concentration reaches a minimum as the dark period ends. A197. Cytosine and uracil are bath components of standard nucleic acids but they do not behave the same genetically. Conversion of cytosine to uracil, by H S 0 3 or any other substance, will change the genetic message. SO2 dissolved in HzO produces H S 0 3 and it is not difficult to believe that inhaling SO2 could alter genes, as could ingesting H S O J in food. Presumably the effect is not great since many cities from 1900 to 1940 had rather high SOz content in their atmosphere. Many adults are quite familiar with the smell of SOz from coal furnaces and fireplaces.
Volume 52, Number 7, July 1975 / 457
