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# OldFinalKey - FINAL EXAM CHEMISTRY 102A Section 04 Answerz...

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Unformatted text preview: FINAL EXAM CHEMISTRY 102A Section 04 December 18, 2001 Answerz KEY NAME (Please Print) Seat Number I pledge on my honor that I have neither given nor received improper aid on this examination. Signature You will have exactly two hours to complete your exam. YOU MUST SHOW YOUR WORK TO RECEIVE FULL CREDIT Before you begin, CAREFULLY READ AND FOLLOW THE INSTRUCTIONS BELOW. Instructions 1. Flip over your exam and print your name on the top right corner of the back page. 2. Check to see that your exam contains all ten pages. 2. Show all work neatly and completely to receive partial credit. 3. Write your final answers clearly and legibly in the box provided. Answers not in the box and/ or not clearly written will be marked wrong. 4. Include units with answers. 5. Direct any questions to the supervising instructor or graduate student proctors. \ Equations and constants: R = 0.08206 L°atm/mol°K ATb = iKbm N0 = 6.022 x 1023 ATf = —inm 1.00 atm = 760 torr H = CRT Kw = 1,0 x 10-14 um = (3RT/M)”2 IIV = nRT page 1 of 12 Q I. Select the one best match for each of the following. (2 points each) Note: Some responses may be used more than once. 1. J) The oxidation number of C in C2042: 2. AA moles of O atoms in 11 g of C02 (44 g/mol) 3. NM % by mass of O in Fe203 (160 g/mol) 4. E Chemical formula fOr calcium cyanide 'Oh oxygen #1 .. ll KN FF 20—3—0: oxygen #2 5. Formal charge on oxygen #2 in ’ ' ' ' 6. ’D A mathematical representation of the relationship between volume and pressure of an ideal gas at constant temperature (Boyle's Law). Let ”C” represent a constant. nitrate t3 It The precipitate formed in the reaction of sodium hydroxide with iron(III) Gaseous compound A (molar mass = 25 g/mol and gaseous compound B (molar mass = 100 g/mol) are allowed to effuse through a small opening in a container. How many times faster is the rate of effusion of A compared to the rate of effusion of B? Spectator ions in the following reaction: 2 K3PO4 (aq) + 3 MgClz (aq) ------- > Mg3(PO4)2 (s) + 6 KCl (aq) 10. 2D Intermolecular force(s) expected to be present in pure methanol (CHaOH) A. CaCN B. Ca(CN)2 C Ca(N3)2 D. PV = C E. P = CV F. PT = P1 + P2 G. NaNOs H. Fe(OH)3 I. no reaction I. PO43- only K. Mg”, PO43- L. K”, Cl- M. K+ only N. Cl‘ only 0. 0.1 P. 0.25 R. 0.3 S. 0.4 AA. 0.5 BB. -5 CC. -4 DD. -3 EE. -2 FF. -1 CG. 0 HH. 1 II. 2 J]. 3 KK. 4 LL. 5 MM. 6 NN. 7 OO. 10 PP. 12 RR. 15 SS. 16 UU. 25 W. 30 XX. 36 YY. 73 22. 160 ZA. dispersion ZB. dispersion. dipole-dipole ZC dispersion, dipole-dipole, ion-dipole ZD. dispersion, dipole-dipole, hydrogen bonding page 2 of 12 II. True/False check the appropriate blank (2 points each 18 points total) True False 11. In general, when comparing molecules with similar mass, a polar molecule will have a lower normal boiling point X than a non-polar molecule. 12. As the concentration of a solution increases, the freezing pt. of that solution decreases. X 13. Consider the following reaction in a sealed container. CH4 (g) + H20 (g) =-‘—‘ CO (2;) + 3 H2 (g) Initially the reaction is at equilibrium. If H2 is removed X from the reaction mixture the amount of CO (g) will increase relative to the original equilibrium amount. 14. In the titration of acetic acid (CH3COOH) with a strong _ base, the pH at the equivalence point is above 7. X 15. The solubility of Mg(OH)2 decreases with increasing pH. 16. Strong acids have strong conjugate bases. X 17. When 0.5 L of H2 at 400 K is increased in volume to 2.0 L at a constant pressure of 400 torr, the temperature will be X 100 K. — 18. A certain metal (M) reacts with oxygen to form a compound with a chemical formula of M203. The metal X could be gallium (Ga). 19. The pH of a 1.0 M HCl solution is zero. Z III. Multiple choice. For the following questions circle the one best possible answer (4 points each). Multiple answers will NOT receive credit. 20. If equal masses of H2(g) and HF(g) are in separate containers of equal volume and temperature, which of the following statements is true? ( a. The pressure in the H2 container is greater than that in the HF container. 7 b. There are more HF molecules than H2 molecules. c. The pressure of both gases is the same. d. None of the above are true. page 3 of 12 . ._.___...‘_.._....-4 . 21. A magnesium ion, Mg2+, has: a. 12 protons and 13 electrons b. 24 protons and 26 electrons c. 12 protons and 10 electrons d. 24 protons and 22 electrons e. 12 protons and 14 electrons 22. The solubility of BaSO4(s) in 0.100 M K2804 (aq) will be? I —. u the solubility of 33304 s in ure water less than the solubility of BaSO4( (s)' 1n pure water. c. the same as the solubility of BaSO4(s) 1n pure water. d. cannot be determined 23. A pH= 4 3.4 buffer 15 prepared from acetic acid, CHaCOOH, and sodium acetate, NaCH3COO. What are the concentrations of acetic acid and sodium acetate in this pH— = 4. 34 buffer solution? 1 00 M CHsCOOH and 0. 40 M NaCHaCOO b. 0.40 M CHaCOOH and 0. 40 M NaCHsCOO c. 0.40 M CH3COOH and 1.00 M NaCHaCOO d. 4.57 x 10'5 M CHaCOOH and 4.57 x 10-5 M NaCH3COO e. none of the above 24. Which of the following aqueous solutions will have the lowest freezing point? b 0.1 m HF c. 0.1 111 NaCl (1. 0.1 m sucrose (C12H22011) e 0.1 m acetic acid (CH3COOH) 25. Consider the following reaction at equilibrium: 2 502 (g) + 02 (g) ———‘ 2 503 (g) If 802' 15 added to the s stem, which of the following statements will be correct? the partial pressure of 02' increases c. the equilibrium constant, K, decreases. d. the equilibrium constant, K, increases. e. no changes occur page 4 of 12 26. Which the following compounds will give an aqueous solution with a pH > 7.0? a. CaBrz (aq) b. NH4Cl (aq) c. AlCl; (aq) e. NaCl (aq) 27. The molecular geometry of P113 is which of the following? a. linear b. bent c. trigonal pyramidal d. trigonal planar e. tetrahedral f. none of the above 28. Which of the following elements cannot expand its valence shell when combining with other elements to form compounds? b. S c. Br d. Xe e. all of the above can form an expanded octet 29. In the gaseous reaction, 2H2 (g) + 02 (g) -------- > 2H20 (5;) 4.0 L of Hz was reacted with 3.5 L of Oz, yielding 3.0 L of H20. The percentage yield of this reaction is equal to which of the following? a. (3.0/7.0) x100% b. (3.0/3.5)x100% c. (3.0/4.0) x 100% d. (3.0/8.0)x100% e. (3.5/4.0) x100% page 5 of 12 16. Use a symbol to indicate if the first item is: (2 pt each) ”>" greater than, ”= ”equal to, ”< ”less than the 2nd1 item Duration of fall break. < Duration of Thanksgiving break. ums of Ar at 400 K ums of Ar at 40 K Strength of a hydrogen bonding interaction Strength of an ion-dipole interaction Normal boiling point for phosphine (PH3) Normal boiling point for silane (SiH4) Rate of effusion of N2 at 300K Rate of effusion of C12 at 300K The volume of 1 mole of ammonia gas at STP The volume of 1 mole of hydrogen gas at STP pH of a .1 M NaCl solution pH of a 1.0 M NaCl solution Acetic acid] / [acetate ion] ratio in a H [ p #4: "”4 3.5 buffer Value of Q when reactants are removed from the reaction [Formic acid] / [formate ion] ratio in a pH 3.5 buffer F k4, : 37% Value of Q when reactants are added to the reaction Production of product if heat is added to an endothermic reaction. Production of product if heat is removed from an endothermic reaction. Concentration of the hydronium ion in 100 Concentration of the hydronium ion in 10 mL of a 0.10 M HCl solution mL of a 0.10 M HCl solution. page 6 of 12 IV. Problems. Put final answer in box. Show your work for full credit. 30. (4 pts) Draw the Lewis structure for the following molecule. a) 131:3 A: 5+ 3(7) = 26 ‘ Nﬂaqf3= 32. 62b 31. (8 pts) Balance the following chemical equations by placing appropriate coefficients in the blanks. Be sure to include coefficients of one (1) when appropriate. No partial credit. (4 pts for each equation) Z A1+ 3 FeO ————— > | A1203+ 3 Fe l_Ca3P2 + LHZO ————— > iCawH» + _2‘_pHa 32. (6 pts) A solution made by dissolving 3.26 g of an unknown non-dissociating compound in exactly 100.0 g of benzene froze at 4.39 °C. What is the molar mass of the solute? K; = 5.07 K'kg/mol. The melting point of pure benzene is 5.45 °C. Hf: ‘lefﬁ’h m1: —AT¢ = ~{43‘l—51LlSWIK' g .2920 1—K; (0 5.07 K43? .925 mu =10 m (manual-— 0-2“!on + .\ao,\7$= 2.0qno'zmo “s 2“, M = __ 3.258 seewlo & £592 20%le?ng w .: 65.4 ﬁ/M molar mass = ‘55-‘61 9 rue-Q page 7 of 12 Q 33. (8 pts) Iron(III) oxide (molar mass = 159.69 g/mol) is reduced to iron metal by CO (molar mass = 28.01 g/mol) in a blast furnace. Calculate the volume of CO at a pressure of 850.0 torr required to produce 1.50 x 103 g of iron metal if the reaction takes place at 1015 °C. FezOs (l) + 3 CO (g) ——-> 2 Fe (1) + C02 (g) T: ‘ 05°C +273 \be1033 Fa * \mQje * sue co >= 4.03xw3me co 2 l : new$5.355? 2MFe W “Am "wow: 3 . W V: £12] __ (Loam MXWMZZZ K) \I: 3 .gbeDSL 5 Volume (in L) of CO = 3-30 K II) L 34. An 87.6-g portion of an unidentified sample composed only of carbon, hydrogen, and chlorine was analyzed and found to contain 28.4 g carbon and 3.18 g hydrogen. A separate method was used to determine that the molar mass was 222 g/ mol. a. Determine the empirical formula. (6 pts) maeaamrfmpﬁl ~mC—WH '7' $7.66 —$3.46 - 3326 a $6.025Cl Fen-owing! .. L'RwQCl Made bumwhem C H U 853453“ LE9 = ‘ dd 3 4 L 2845c 1%c = 2.354M96 g; ' My“ 5",; = mm?” .9 “TM” mom I? u a- stﬂl- = 3455.04 h“ ' ‘53 W“ ““3 b3 7' ’5. 3 IlfwnsMDetermine the molecular formula. (2 pts) =‘7 7'4 Cl {SM cl bl WWI-”H 0344M; mm = 3603 a W” SNQCJ‘ Wk» 3 “to Wolw‘g'” M N xcE‘FB Cb‘l'lgC/l‘k page80f12 — Mp: ' Q Zwe 61* 32355: 70-4504 9:: 722‘? = 2.0 N_/— “/0555 M wijmriwaboy 1.031.709: mom, mmammgwmgm. u r . 35. Consider 25.00 mL of 0.250 M acetic acid, CH3COOH. (Ka = 1.8 x 105). a) What is the pH of this solution? (6 points) cu +Hc>4——Ho'* c ‘ 3032““? 2 --7 3 “0+ “£024.25 .751)“ 4.0 O I 0, -)€ 47‘ * )L E .2So—x x 54 R0" ﬂabQthoﬂ : (9000 MW x<4 .750!“ [cage 1H3 (390—13 4' v H = 409030 3 Ken: 2,6,: 91+ : 4&05L2.\2¥Io‘5> b) If 12.50 mL of 0.500 M NaOH are added what is the resulting pH? (6 points) t2-50mL a- «500W : 6.25% 00,091 «arm, manai 1 1 ML ML g. 350%,,2 5 6.2!:M aﬂscozH 3. WOW pt ML 526 J \U? H . M ' 00300; ”a? :44 94+ “3"“ 559». [mama] V (12-§+ zst: weak W ! 1'4 Kb: Kw : LOX”)— cH co“ 4,“ A Maud-l2. 0H: 3 K,“ l-‘BXID’S 3.52%) 2‘60) 7 o ('0 “0°93 Kw- 555me : LK +)§ +X E Jb‘r-x ’X ‘K gqg pH= Mb- [W .(M 43 Ccu3co; 467% (ii = \q+$2»5(q.eaxro pagegoflz MW “(.4 Ab? W Ky. 16‘ {ﬂights = -\bT(65bxto"') Q _ :— 43¢ [“43 JG? 7': ‘Zg '0'” 'XsinJ ?0H’” 5 .5 - 0’“ 36K: 3.63369 Mb pH W i” 36. (12 pts) The solubility product for Can in water at 25°C is 4.0 x 10-11. a. What is the molar solubility (mol/ L) of Can in water at 25°C? (6 points) - - 2. 2 F' Ksp=LLO¥IO n K5? : [Coy-3U: ] I C0-F(s\—7 Ca. 099 + 20 (as) C +5 +Zs E s 2 5 KW: 5(25)‘ 2 463 3 41 5: “HR“ = 2\leo‘q if solubility= 2.15wo' 4M L, b What IS the molar solubility of Can at 25°C in a solution of 0.060 M Ca(N03)2? (6points) CA? (a): Ca2+ +21: 1 .%H 0 #3qu _C/______’_'.___er_‘>.4_&s__ '5 .oms '25 “5?: (054’sz9)?’ 046W $<4 .Olo [15‘0” (WWW &%YW1)4HDH:-3- 5: ’24 a I. zﬁxm solubility = ! page 10 of12 Q 37. When 820.0 g FeCrO4 (molar mass = 171.84 g/mol), 250.0 g K2C03 (138.21 g/mol), and 80.0 g 02 (32.0 g/mol) are reacted, 194.0 g KzCrO4 (194.19 g/ mol) are produced according to the following reaction. 4 FeCrO4 (s) + 8 K2C03 (s) + 7 02 (g) -—~> 8 KzCrO4 (s) + 2 F6203 (s) + 8COz (g) a. What is the theoretical yield of K2CrO4? (6 pts) manor (Limo 3M KZCA‘Oq Elli-’19:), P253 KCrO a owmza “aqua Emmi“ “‘9 6 z (e 2505 \42003. mung, * ‘3’va K393, * mange, : 1351.33 K1099] Ksza liming {5%.ZI 8 3 M K2603 3°30: ,. M 0,. 1 W21 1% (42%. 564.25 mm 31-06 '7 a7. theoretical yeild = 35 i 3$3 sz‘f b. What is the percent yield of the reaction? (2 pts) \$61014 : imiifmﬁ 351:); 1d a o y1e = 38. Consider 100.0 mL of a buffer that is 0.500 M in formic acid (HCOOH) and 0.500 M in sodium formate (NaHCOO). If 8.0x10'3 moles of HCl are added to this buffer solution Without changing the volume, what is the resulting pH? (Ka of formic acid = 1.8 x 104) (6 points) Ime+.5£m9 —. Sammie Hcogrl i send ManL ML Hal + NatHcoz ’9 ”0149.23 4 ”cozHcag) (3 (‘63 HQ; aﬂcsfw‘ouxn w/HCI) 1 2M 42H - . H60— : L—— =. ' n " 5 5-0on NGHCO *gwwon‘a 2' 42mg RCO; t 2 [DOML ”’ ’ g 53.....4 m... Lw.u1=s.:__w~e0=5w i “COM + a " iOOwL Mm,“ = 60M z (WW\ I mud/Hf"l o H oz— 0+ 4 £460; \ Q H‘nglrl‘r Z 7+}: .47, pH= 3450 c. + +)u 4K 5 "55% x 42+): page 11 of12 WM {4 "EL Q K4 .[Haoﬂﬂlﬂﬂz :i _ ﬁll“ it 76 (35% y.- Mebm‘“: {H305 ' 7H - vﬁag(2-It‘lslo'*)s 3.2 ...
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