Questions Q 315. Chicago area drinking water contains 0.018 ppm of Hg. Does this concentration seem dangerous if the toxic dose is assumed to he 300 @g/day? 6316. A dieting lady in New York City ate 0.35 kg per day of tuna which contained 1ppm of Hg. How does her daily dose, which led to obvious poisoning symptoms, compare with the presumed toxic dose of 300 rglday? Q317. There are 2 X 1015 kg of COz in the earth's atmosphere. Humans annually hurn about 6 X 1012kg of carbon as fossil fuels. If none is removed, what is the annual percent increase in atmospheric COz? Q318. About 8 x 10's ka- of oraanic - carbon is buried in sedimentary rock, wiih about 0.1% of this amount possibly recovrrahle as fossil fuels. If all the recoverable fossil fuels (assumed to be pure carhon) were burned what fraction of the atmospheric oxygen would remain? Suppose all the buried carbon were burned; now what fraction of the atmospheric oxygen would remain? Comment on any meanings you extract from these numbers. 6319. Total stream flow in the US is about 1013cm3/day
containing 10 ppm dissolved 0 2 . The US also produces about 2 X lo9 kg of biological oxygen demand (BOD) per year. How does the BOD compare with the total oxidizing capacity of the water flow? Comment on the effects. 6320. Sodium tripolyphosphate (NaTPP, NasP3010) is a standard ingredient in many detergent formulations. Write the equation for its hydrolysis to Na+ and Pod3- and account for the resulting pH of about 11. 6321. The average coal contains ahout 3% sulfur. Coal costs about $6 per 103kg. Sulfur sells for about $32 per 103kg. Large power plants hurn about lo7kg of coal each day. How much can such a plant afford to spend annuallv on sulfur recovery without inrreasing the cost of elrctricity to the user. Q322. The IJS produces 1OYkalvr of lindane and similar pesticides. ~ s s u m e t h e s eare all washed into the ocean (containing 1.5 X loz1kg of HzO, of average depth 2 km, with the top 300 m rather well mixed each year). Is there any danger to phytoplankton, whose photochemical efficiency drops rapidly if lindane is present a t 10 ppb (10 parts in lo9). How about shrimp whose mortality is 50% a t 0.4 pph lindane?
Answers A315 An average person drinks 1-2 1of water per day. Assume 1 llday consistent with Q14, (This Journal, 49,181 (1972)).11 = 1000 g; 1000 (glday) X 0.018 X 10Pg Hglg Hz0 = 1.8 X (g Hglday). This is 18 X (g Hglday) or 18 pg Hg, about one twentieth (0.06) of the toxic daily dose. There should he no prohlem if the data are correct. A316. 0.35 kg = 350 g. 350 g tuna X 10W (g Hglg tuna) X lo6 pglg = 350 pg Hglday, well over the daily toxic dose of 300 pg Heldav. ... A~L'I. C u + O Z ( ~=)C02(s) [I00 X 6 X 1012kgC X (44g C02112g C)]/[2 X 1015kgCO*] = 1.1% increase in atmospheric COz per year if all COz comes from fossil fuels and none is removed. Actually, of course, there are other sources (ex. decay), and much is removed (ex. by photosynthesis). A318. c1.1+ 02(g1 = C 0 ~ 1 ~ ) heoverahle) X 32 ke.. 0.,/12e 8 x 10IRkeC X - C = 2.1 X 1016 kg 0~rcquiwd. Almo~pherirpresrure is about I5 p.s.i. runfortll~witelymmt uf US st111know this figure in English u n i t s only1 of amrh ahmrt 0 . 2 R~pwnd/in2i~due rooxypen. Thediameter of
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Burning all the recoverable carbon wouid require 100 X 2.1 X lfl'VI1.4 X 101fil= 1.5%oftheatmosohericmveen. ,.. ..orobshlvwith negliiible effec;on the ntmosph~re.but note, there is iniufhcirnt oxygen bya lacwr of 10 to burnnll the~edimentarym r h n lfunc aisume.; all the carbon came from (:01then iome of the oxsgrn released in the prncess has already been used elsewhere. It is aenerallv assumed it was used in oxidizing- exposed minerals, e.g. . iron. A319. BOD measures the oxygen which would he required ta midize completely the waste praducta. The figure given is 2 X 109 ~
498 1 Journal of Chemical Education
kg of Odyear. Total oxygen in annual stream flow =1013m3/dayx kglg = 4 X lo7 (kgOzlyr) 365 dayslyr X 10 X lo-" 002/cm3X in the streams if BOD = 0. The BOD is about 50 times greater than the total oxygen dissolved in the streams at any one time. Thus, very long stretches of many streams will be seriously contarninated, until further oxygen can dissolve and replace that usedup by the BOD. Dams, weirs, and rapids help speed this solution process. A320. The requested equation for the hydrolysis is ~
~
PLIOIO~-(~~I + 2HsOm = 3POFjegi + 4HC(*q) However, POa3- is a strong base in water and forms HPO1%3POP-1,)
+ 4H+(.,)
= 3HP04z-(,)
+ HC[.,)
HPOP- is still a stronger base than Hz0 SO also hydrolyzestosome extent. 3HPOP(.,,
+ H+(.q) + 2H20(1)= ~ H Z P O ~ +- (20H-(ss) ~~)
The principal equilibrium is between HPOP-, H2P04-,and OH-,
($Iyr)could be spent on sulfur re-covery. Note one significant figure. This assumes noother gains (like public relations, for example) from removing the S. A322. lo9 (kg lindane/yr)/[ld X lo2' (kg H20) X (0.312) (kmlkm)] = 5 X 10-l2 (kg lindanelkg HzO)per year. This is 0.005 ppb. Thus,if the lindane is uniformly dispersed there is no apparent problem. But note this value is only 0.01 the lethal dose for shrimp and 0.0001 that of phytoplankton. These levels would almost certainly he reached somewhere, but not often.
