Small things and large numbers

edited by ROD O'CONNOR Texas A8M University College Station. TX 77843

Small Things and Large Numbers Milton H. Rosenburg Pace University. Westchester Campus Pleasantville. NY 10570 1) Cinnabar (HgS) is one of the more commm mercury ores. Mercury(ll) sulfide is une of the least solulrle of all chemical sal& having a solubility product of about 1.6 X 1(1-'~. Hou many liwrs 01 i l saturated aqueous solution of HgS would he rewired in order LO have onr dissulved He'- ion? (Note: ~ l t c o u g hnumerical calculations are apGicahle, thev have no real exoerimental validitv a t such low concentrations.) An ecology-conscious gardener finds a container of DDT with about 0.78 lb left. Wishing to dispose of it properly he goes on a trip around the world and distributes the DDT evenly in all the oceans. After the DDT has mixed thoroughly in the oceans (this may take some time) he draws a &as; of water from tht*nearest orean. How many molerules of DDT would h~ expect to find in this sample? 111 mav heln in the solution to~knowthat the volume of all the w a k r in the oceans is estimated as 1.3 X loz1 1, that a tvoical holds 0.25 1. and that it iust h a. ~. ~ e n s .. drinkine elass . that 0.78 ltr of DIH' isahout a mule. R'e may assume, also, that thpre is no loss of I)IYI'.J 3) A careless lecture as;iistant accidentally released 10 ml of H2.i (at 7G0 torr and 27°C) in a closed lecture hall 20 m long, 15 m wide, with an average height of 4 m. Alter the HkS was uniformly diitrihuted, how m a y molecules of H2S were inhaled by a student taking a "full deep brwth" (1.01K'

-

Answers (1) about 1300 1 (2) about 120 molecules (3) about 2 X 10" molecules Detailed solutions available. Address your requests to Rod O'Connor, Department of Chemistry, Texas A&M University, College Station, TX 11843

962

Journal of Chemical Education