2005年第37届IChO预备试题答案（英文）7-12无机化学

69 Answer 7 Atomic Orbitals 7 1 1s 0 2s 1 and 3s 2 7 2 2p z 3p z There is one angular node for 2p z one angular node and one spherical node for 3p z 7 3 0 2 4 1 3 Answer 8 Intermolecular Forces 8 1 1 Na OH 2 OH 2 OH 2 H 2 O OH 2 H 2 O 8 1 2 70 O O O O O O Na 8 2 1 F H F H F H F H F H F H 8 2 2 CH 3 C O O CCH 3 O O H H 8 3 N N N N N N H O OR H H 3 C NH H H R H Thymine Adenine N N N N N N NH H O R H H H O NH H R H Cytosine Guanine 71 Answer 9 Crystal Packing 9 1 Simple cubic 6 body centered cubic 8 and face centered cubic 12 9 2 For simple cubic a 2r 4 52 a 3 4 f 3 3 v r For body centered cubic ra 43 68 a 3 4 2 f 3 3 v r For face centered cubic ra 42 74 a 3 4 4 f 3 3 v r 9 3 ra 42 pmra 40722 3 3 23 g cm 6 10 407 1002 6 9 107 4 pm d 9 4 pm 22917 34 sin2012 sin2 o d Answer 10 Applications of Transition Metals 10 1 1 2 CrO 4 2 aq 2 H aq Cr 2 O 7 2 aq H 2 O l 10 1 2 CrO 4 2 6 Cr 2 O 7 2 6 10 1 3 This is not a redox reaction because the oxidation state in each metal center does not change 10 1 4 Hydrogen ion concentration is the main factor to control the equilibrium position 72 10 1 5 Cr O O Cr O Cr O O O O O O O O 2 2 10 2 1 12e 4e O 2 Cr 2 O 7 2 aq 2 H aq H 2 O l 3 O 2 g 2 Cr s Cathode Anode Overall Cr 2 O 7 2 14 H 2 Cr 7 H 2 O 2 H 2 O 4 H 10 2 2 1 5 moles of oxygen gas will evolve 12e 4e O 2 Cr 2 O 7 2 aq 2 H aq H 2 O l 3 O 2 g 2 Cr s Cathode Anode Overall 3x 52 g Cr x 1 mol Cr 52 g x 3 mol O2 2 mol Cr 1 5 mol O 2 Cr 2 O 7 2 14 H 2 Cr 7 H 2 O 2 H 2 O 4 H 10 2 3 16 h 52 g Cr x 1 mol Cr 52 g x 6 F mol Cr 16 h x 96485 C 1 F x 1 sec 10 C 1 min 60 sec xx 1 h 60 min 10 2 4 Chromium readily forms a thin adherent transparent coating of Cr 2 O 3 in air making the metal extremely useful as an attractive protective coating on easily corroded metals Answer 11 Electrochemistry of Inorganic Compounds 11 1 For the concentration cell Mn s Mn 2 aq 1M Mn 2 aq MnCO 3 Mn s 73 E cell E o 0 0592 2 log Mn 2 right Mn 2 left K sp 1 8 10 11 Mn 2 CO 3 2 Mn 2 right 1 0 10 8 M and Mn 2 left 1 0 M with E o 0 0 V both are Mn E cell 0 0 0 0592 2 log 1 0 10 8 M 1 0 M 0 237 V 11 2 Reduction of O 2 to H 2 O is obtained as 0 70V 1 76V 2 1 23 V for O 2 4H 4e 2 H 2 O E o 1 23V The E o value could be obtained directly from the diagram by dividing the differences 2 46 of O 2 and H 2 O by the differences of the oxidation number 2 For H 2 O 2 O 2 H 2 O E o 1 06 0 0 The disproportionation reaction is spontaneous 11 3 The number of electron pair should be 5 trigonal bipyramidal with three electron pairs in the equatorial plane thus the molecular geometry of XeF 2 is linear 2 H 2 O O 2 4H 4e E o 1 23V XeF 2 aq 2H aq 2e Xe g 2HF aq E 2 32V 2 XeF 2 aq 2H aq 2 H 2 O 2 Xe g O 2 4HF aq E 1 09 V The decomposition of XeF 2 in aqueous solution is favored in acidic solution Answer 12 Metal Carbonyl Compounds 12 1 Compound A is anionic the absorption bands attributed to CO stretching appear at lower 2H2 00 2H 74 frequency because of stronger back donation of the anionic charge to the anti bonding orbital of CO thus weakening the CO bond For the neutral species B absorption bands appear at the higher frequency 12 2 W OC CO CO W OC COOC W OC CO CO C CH 2 W OC CO CO W OC CO CO W CO 6 NaC 5 H 5 Na HCCCH 2 Br FeSO 4 Na Hg metal migration A B C D 12 3 C CH 2 W OC CO CO W OC CO CO D D metal migration C D