Chem206_2007_Prelim1_AnswerKey - Page I of 7 Chemistry 206...

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Unformatted text preview: Page I of 7 Chemistry 206 Preliminary Examination 1 September 27, 2007 Name E 1 TA: 1. — 6. /30 7. n4 8.’ /23 9. /24 10. /50 11. /34 Total /175 Exam lasts 90 minutes. Plan your time accordingly. Some usefiJl information is provided on p. 7. Strict adherence to the Code of Academic Integrity is required of all students. Page 2 of 7 MULTIPLE CHOICE — CIRCLE THE CORRECT ANSWER: (5) 1. Most of the elements found in nature: a) are nonmetals b) are rare earths d) are semi-metals e) have an equivalent number of protons and neutrons (Si 2. Krypton (Kr) is a: a) metal b) noble gas c) rare earth (1) semi-metal e) chalcogen (5') 3. In which one of the following sets of atoms and ions do all species have the same number of electrons? a) B', Kr, Sr2+ c) Mg 2+, Sr“, Ba2+ d) O, 02‘, 02+ e) none of these (5) 4. What kind of reaction is represented by: Pb(NO3)2(aq) + 2KBr(aq) —> 2KN03(aq) + PbBr2(s) a) net ionic b) precipitation c) single replacement d) synthesis e) neutralization ( 5) 5. The spectator ion(s) for the reaction described in #4 are: a) Pb2+ b) N03' 0) Br" d) K+ e) (a) and (c) t) (b) and (d) (S) 6. Consider the following calculation: (6.23 x 0.042) + 9.86 The answer With the correct number of significant figures is: a) 10 b)10.l d)10.122 e) 10.12166 (é. 23 x 0.042.) = 0.2.6 +wo Signsfl-cant 33mm 0. 2 z, 51...: as 10 I 2 +UJO QJIE’fljKT":‘zI lD/thes Page 3 of 7 SHOW YOUR WORK IN SOLVING THE FOLLOWING PROBLEMS. Circle your answer. If you need more space, use back of page and mark clearly. Move circled answer to space under question. (“I i 7. if a marathon racer runs 26.22 miles in 3.25 hours, then how many miles does she run in a nanomole of seconds (assuming she keeps up the same pace). 3 b r , -’- 13 min ‘ hr ‘ Willi? X W“ “ ’0 qf;°""_"?u)?e‘i I2. .. Lgs x10 miles. p _‘”___‘.,_»--—we M W“ 8. A portion of food is combusted within a bomb of a calorimeter that contains 200 kg of water. Energy is released, and the temperature of this water that surrounds the bomb increases from 22.1 to 38.7°C. (l 5) a.) What is the energy content of this portion of food in Calories. 3 C/ . ode. r 2 O X10. - °C. 3%. ,1 5/3 c c he oi W I: O O S ZZ.| 2.0a K103 a some-er AT: 16.65C X Cg Mo'me “Oooxlg'sc><z’00x'°3%3 _,__-.__._51:,.._°£-_---. 2‘33-1 lemmak LW,,_,.....W.WM-WM * (3') b.) You read in a newspaper that splitting a specified amount of H2 molecules to H atoms in an “H bomb" releases 5.0 x 109 joules. Explain why you should not believe this report. EHQP‘EY 75 refutier +0 break bomdh (Energy is 93+ released) 9. Element Q has 2 natural isotopes 35Q and 37Q. Assuming natural abundance, the mass per atom of Q is 35.45 amu. (I 0) a) Identify Q in the periodic table, and specify how many protons, neutrons, and electrons in each of JSQand3Q From 035mm “Misfit “WWW Q3.CHE$W> :7 - ['7 eiem‘rems [fig net—Acf‘r'oft‘i: mum-mm“...- Page 4 of 7 (¢) 9.b) What is the mass of a mole of Q atoms in grams? IF One attam 1'5 35.45 chj 1‘qu (Dire. arm-pr- mole of Monte i5 ‘ Sis/“Eff (a) c) What is the mass of a molecule of Q2 in grams? Q ' 3:5 X Z 1”"“e4éafssal a» I m , “Amman...” 7.4. - vw ~1ku:WiW"~"‘""“‘" "-- ‘I " (“2.x i033 m+o”‘\3>‘/m”\’9/‘<- =-. /,/2 x/O'J‘Z /MO{C—C.UL’{_i 10. Silicon nitride (Si3N4) is a desirable ceramic material that withstands high temperatures. Si3N4 can be produced by reacting silicon tetrachloride (SiCl4) with ammonia (NH;). In addition to Si3N4, hydrogen chloride (HCl) is produced in this reaction. There are no other reactants or products. Go) a) Write W: this reactigpLuhmmwk 3S:’Cl«/ + ill/VH3 "‘9 51th “Mer (No) b) If 128g of SiCl4 is reacted with 10.2 g of NH3, which of these two compounds is the limiting reactant for the production of Si3N4? SiCl/f. 2%,0‘3 4- L/ (35.45”): Moot? 3/14/1014; Mao; + 3(I.Oo7)-w 17.03 3014.00. W3 SW“ iiég‘fa/tg—i- 3 0126' -' M M143, 10.2. $2 :7 LI, Yfim £0,150 reed—ions l7.o‘5 Slmou. Page 5 of 7 (I b) 10.c) Assuming the conditions of part (b), how many moles of Si3N4 can be produced theoretically? .I“ We a; 5W P*°W”<.f5’ emfl We o£ NHs Qantsumed .',l OJSL‘) _m§zes ott- [Ores oLHceo( based 0/? COL/WCM W ' [I ‘I . - L - Dr W ) _, OJSQ Malena at; 5‘; u t .. I I’LO3 affinities ‘4 We We (3) d) If 11.4 grams of Si3N4 are actually produced under the conditions of part (b) what is the percent yield of the reaction? [If you didn’t complete part (c), assume that answer is 0.12 moles] Shim, .. 3(az.os)+<i(1%orl= [40,3 glmole. Mm... "www.mtuaa—m -z. 0 Li- : g, [3)(10'2' Mot“ SUJ. M’lxloo: $K3°7e Hoe; 3 9 1,5029!) yi cl 4 11. Elemental analysis of unknown compound X showed that it contains only C, H, and 0. An experiment shows that 47.20g of X decomposes completely to its elements in the form of 18.9g C(s), 25.15g 02(g), and 3.17g H2(g). (3) a) What is the % composition of each element in the original compound X? Ante! Mass : go} + 25,15 + 3J7 -: 47.2.3 070 Compost-60m r———-—__.An‘._._..~7n - ‘ ____,_._,__ ‘____ Page 6 of 7 (I 0) Mb) What is the empirical formula of the compound? is? , a: [2'0 2: 0; 234.5 1 (I) O c) The molar mass of compound X is determined to be 60.05g, what is the molecular formula for X? CHZo: 12+ztnoi)+~l<o= 30.0 31mm. . K .... “#4.,- _-:ma_w _,. 0.0:“ 1w“! ' fad—i: L fi CZ O; Sta-D <1 W (3) d) If all the gaseous molecules produced in this reaction are captured in a sealed tube of volume 5.0L, what is the density of the gas in this tube (assume that no other matter is contained within this tube). 7 ‘3, 0L] - “a! a ‘ _, EM”..th “mm,” mm .— ...
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Chem206_2007_Prelim1_AnswerKey - Page I of 7 Chemistry 206...

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