ST ROUND, PROBLEMS

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1 ST ROUND, PROBLEMS Solv all or som of th problms givn on th nxt pags and writ your full solutions in MS Word, Excl documnts or *.pdf fils. It is also accptabl if you scan your matrial and insrt as pictur in mntiond fil formats. If thr ar som xplanations rquird, writ thm in English. Plas, snd your answrs to: kimijas_olimpiads@inbox.lv till at 3: (Latvian tim; ). Answrs snt aftr this dadlin will not b gradd. Fil nam must consist from your nam, last nam (in English) and country, for xampl, John_Black_England.doc (or *.docx tc.). If you do not nam th fil as dscribd you will rciv 3 point pnalty. For all th corrctly solvd problms you can gt th maximum of 3 points. Th xact amount of points for ach task is givn at th top of ach problm. All th studnts who will b taking part in at last on round will participat in th final round which will b hld on th wb on Fbruary 7 th. During th final round you will hav to solv th multipl choic tst. Mor information can b found in BCC rgulations. Comptition organizrs and problm authors: Kaspars Vldr Vladislav Ivaništšv Egl Maksimaviciut Filip Topić PhD studnt, Univrsity of Latvia, Dpartmnt of Chmistry PhD studnt, Tartu Univrsity, Institut of Chmistry nd yar BSc studnt, Vilnius Univrsity, Dpartmnt of Chmistry Croatia Ptr Holzhausr Czch Rpublic Agris Bērziņš MS studnt, Univrsity of Latvia, Dpartmnt of Chmistry Good luck with problm solving! 1 Karina Kizjakina PhD studnt, Virginia Polytchnic Institut and Stat Univrsity, Dpartmnt of Chmistry Alons Lnds BSc studnt, Riga Tchnical Univrsity If you hav any qustions, you can addrss thm to us in English by snding thm to: kimijas_olimpiads@inbox.lv Fl fr to ask!

2 Problm 1 (Lithuania) Sulfur containing gass (8 points) A 5. L closd containr was filld with SO (7% of total volum) and O (3% of total volum) gass, th tmpratur insid th containr was kpt at 5 C. SO.5 O SO 3 raction occurs at 5 C. 1. What will b th final volum of th O in that containr aftr th quilibrium is rachd? 1. L of watr was addd into th sam containr kping it still closd.. Writ th raction that occurs upon th addition of watr? What is th ph of th rsulting solution? 3. What would b th ph of th solution if th tmpratur insid th containr (during th addition of th gass??) would b at C? Aftr adding watr th solution is coold to 5 C.. What would b th ph of th solution if th initial proportion of gass is 3 % (SO ) and 7 % (O ) of th total volum (at 5 C)? 5. Is it possibl chang concntration of hydrogn ions in solution to b two tims highr or lowr than in part by changing tmpratur or initial proportion of gass? If so thn how? Show th calculations. SO SO 3 O Δ f H o / (kj mol 1 ) S o m / (J mol 1 K 1 ) All rquird constants can b found onlin or in handbooks. Rfrncs should b givn to th sourc of information. Problm (Estonia) Blss you! (1 points) If too many drugs ar providd against on illnss, thn it mans that this illnss cannot b hald. Anton Chkhov Schm 1

3 Writ th structurs for compounds A E. Do you agr that in cas whn nitrogn atom carris thr diffrnt substitunts it is chiral, bcaus of its lon lctron pair that plays th rol of th forth substitunt? Why? Schm Writ th structurs for compounds A E, Х. Writ down th structurs for all of th compound B stroisomrs and assign configurations at thir strocntrs. Problm 3 (Latvia) Quantum organic chmistry ( points) β Carotn is an organic compound that is classifid as a trpnoid. It is a strongly colord rd orang pigmnt, abundant in plants and fruits. As a carotn with bta rings at both nds, it is th most common form of carotn. It is a prcursor ( inactiv form) of vitamin A. β Carotn contains a conjugatd chain of carbon atoms with an avrag intrnuclar sparation of 1 ppm. Th π lctrons in this conjugatd chain ar dlocalizd and, to a rough approximation, thy can b considrd to b particls in a on dimnsional box of 3.17 nm (that is x1 pm)lngth. Each carbon atom contributs to on π lctron. 3

4 1.. Calculat th diffrnc in nrgy btwn th highst occupid π lctron nrgy lvl (HOMO) and th lowst unoccupid lvl (LUMO). Calculat th wavlngth of radiation that would b absorbd in producing a transition btwn ths two stats. Problm (Estonia) Chmistry of points) radioactiv particls (8 Part 1 Radioactiv dcay quations Radioactiv dcays ar classifid by ruls of Fajans and Soddy into two groups: α and β dcays: A A- X Y A A X Y Y 1-1 H α dcay, β dcay, A X A 1 Y 1 β dcay. Complt following quations and, if it is possibl, dtrmin th typ of radioactiv dcay. 1 n Tc 8Pb H 8 B H Cd Tl 6 C N I Bi 6 81 Tl 19K Nd H 86Rn 18 8 Po 68 31Ga 68 3 Y 18 6 Sm 1 Nd Ra Part Masuring radioactivity For masuring activity of radioactiv particls SI masurmnt units, bcqurls (Bq), ar usd. On bqurl corrsponds to on dps (dcay pr scond). Masurmn nt units as dpm (dcays pr minut), Bq/kg or Bq/mL ar drivd from Bq that way to show th numbr of dcays pr mass or volum of radioactiv matrial. Bsids SI units non Si unit, curi (Ci), is also usd for dscribing radioactivity. On curi is qual to Bq and originally it was dfind as activity of 1. grams of radium 6. 1) Calculat half lif of 6 Ra (in yars) using dfinition of curium. Latr, half lif of radium 6 was dtrmind mor prcisly and it appard to b T ½ = 16 yars, but masurmnt unit Ci was not changd and it is still bing usd for approximat calculations. ) Calculat mass or radium which has activity of 1 Ci.

5 Radium was discovrd in 19 by Pirr Curi and Mari Sklodowska Curi. From 8 tons of uranium or wast thy obtaind 1 mg of radium chlorid. 3) Calculat activity of obtaind radium chlorid in Bq pr kilogram (Bq/kg). In 197 Mari Curi giftd 1. g of radium to Institut of Radium in Paris (now Institut of Curi), whr it is still kpt nowadays. ) Calculat amount of radium (in mols) which was not dcomposd in th tim priod from 197 to1. 5) Calculat mass of radium (in g) dcomposd in this tim priod. 6) Calculat in what yar practically all radium will b dcomposd (99.99%). Part 3 Equipmnt for masuring radioactivity Radioactivity of particls is masurd by spcial quipmnt. Not all masuring dvics ar up to dat so it is vry hard to dtrmin th corrct valu of radioactivity. With th aim to improv radioactivity masurmnt, instrumnts ar calibratd using spcially prpard spcimns. 35 Such matrial is 16 S (T ½ = 87.9 days) with initial radioactivity.1 μci. In days, radioactivity of this matrial, dtrmind by Gigr countr, dcrass to 6 dcm. 35 1) Calculat actual radioactivity that 16 S will hav in days (in Bq). ) Calculat snsitivity of Gigr countr (in %). 3) Calculat radioactivity valu dtrmind by this Gigr countr aftr 7 days for 1 mg 51 Cr sampl (T ½ = 7.8 days). ) Calculat mass fraction of 51 Cr in obtaind sampl (aftr 7 days). Part Dangrousnss of radioactiv lmnts At th momnt of Earth formation, radioactiv lmnts wr part of svral chmical compounds. Som scintists associat high tmpraturs in Earth cor with th radioactiv hat. Existnc of radioactiv lmnts with long half lifs (for xampl: uranium yars; thorium yars; potassium yars; rubidium tc.) is supporting this statmnt. Othr lmnts with shortr half lifs ar formd at dcay of uranium 38, thorium 3, and uranium 35. Radium, polonium, and radon ar among thos nwly formd lmnts. Du to ffct of diffrnt wavs from univrs on th Earth atmosphr, radioactiv carbon 1 C (T ½ = 57 yars) and tritium 3 H (T ½ = 1. yars) ar formd. Radioactiv background xists at all tims, and is formd from both natural and man mad radionuclids. For xampl, contnts of radioactiv isotop of potassium K (T ½ = yars) in natur is qual to.117%. All othr isotops of potassium ar stabl. 1) Calculat radioactivity of mtallic potassium (m = g), found in school laboratory. ) Stat at last two rasons why potassium from school laboratory is considrd to b saf. Espcially dangrous isotop is strontium 9, which rplacs calcium in liv organisms and accumulats in bons. 3) Explain why strontium 9 is so dangrous, nam two illnsss causd by radioactiv strontium. As a fact, cigartt contains from 3 to mbq of 1 Po. Aftr ntring human organism, most part of 1 Po accumulats in bons, tth, and also in kidnys and livr. ) Calculat tim that is rquird for complt (99.99%) dcomposition of 1 Po (T ½ = 138. days) aftr smoking on cigartt. 5