fianl spring 01 - CHEM 14A Final Exam sp 2001 (“’7 Mac...

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Unformatted text preview: CHEM 14A Final Exam sp 2001 (“’7 Mac oat-3W Wednesday, June 13 Prof. H. D. Kaesz a; $0M 11:30 am — 2:30 pm T.A.'s: Mike Bedard, Tom Mil er . NAME: I|II||IIIIIIIIIIIIIIIIIIIIIIII |III|III||I|II||I||II||I|III| LAST FIRST STUDENT I.D.: | I I I I | I | I I I I I I I | I | I | SIGNATURE INSTRUCTIONS: I Question I I _ I 1.Please sign above. I Number I Max. I Score | I I I I 2 . Answer each question in the space provided. I 1 I 34 | | I | | l 3 .Where reasoning is requested, this should be. I 2 I 33 I I well organized and legible. | I I I | 3 I 33 I I 4.All answers MUST appear on respective pages. | | I | ' l 4 | 34 I | | | I | I 5 | 33 | | I | I | I 6 I 33 | I I I | I | TOTAL I 200 I I CLA'SS Ave: 97 Two sheets containing the PERIODIC TABLE and other information will be separately distributed. FINAL COURSE GRADES AND RETURN OF FINAL EXAMS To receive notification of your course grade, please submit a self-addressed postcard. To pick up your final examination please leave a stamped, self-addressed 9” x 12” manila envelope at the Chemistry Receptionist, Young 3034, or in the box outside my office, Molec. Sci. Bldg. 1505, and the exam will be mailed to you: the envelope plus exam requires 55 cents postage. pagel Name (2mg: 4 1. (34 points total) a. (12 pts) Referring to the Tables of bond dissociation energy, estimate the energy change accompanying formation of ammonia in the gas phase reaction N2 + 3 H2 = 2 NH3. Show method. Ans. 2% kJmol‘l .f. 7,20%.— 2518 = “/z7/kf b. (6 pts) Given a mixture of N2, H2 and NH3 that is at equilibrium, circle one of the following three transformations which will occur if the s stem is com ressed int a small r volume while equilibrium is maintained. (A) some of the N2 (B) some of the NH3 ' or (C) there and some of the H2 must decompose will be must combine to give into N2 and H2. no change. c. (8 pts) For the reaction N2 + 3 H2: 2 NH3, K = 6.8 x 105 at 298 0C. What is the value of K for the reaction: 1/2 N2 + 3/2 H2: NH3 at 298 °C? 2 Show method. Ans. K = Zl/x '0 at 298 °c - WA , . L ' (NA/4H,)?» : gum/o d. (8 pts) The energy change for the reaction PCl3 + Cl2 = PCl5 is —88 kJmol" at 298 °C. What will be the effect of heating this reaction to a higher temperature? Ans. The reaction will A... . shift to the right, or shift to the left or, remain unchanged Briefly explain. / page 2 Name (M %4 2. (33 points total) a. (4 pts) Using the qualitative conductivity apparatus of a light bulb connected to a 120V AC circuit through two open electrodes, was crystalline sodium chloride shown to be a weak, strong, or @- conductor. Explain. Ans. conductor ‘ M a M; d) L If; weak, strong or. ball,“ a a” b. (4 pts) What type of conductivity is indicated when distilled water is added to the crystalline sodium chloride in the apparatus described above? conductivity Explg'n. \ Ans. _ - ~ ~ - W weak ; r non- A/a M (>3 ms ‘1 W/“JAO W 5143* (“W112 a“ $04qu: w?» W aM‘M—r c. (6 pts) A 0.561 g sample of KOH is dissolved in 50.0 mL of water. What is the pH of the solution? Show method. Ans. pH = ' 7’ M M“ “0 ’4 56” 7KOw/MKM4' P14 P]; - I (I H 1" : I O _ / O 2H+2§°Hq=lo i0" ’ d. (6 pts) How many mL of 0.125 M HCl solution are required to titrate 50.0 mL of a 0.100 M solution of KOH to the equivalence point? Show method. ) Ans. 40 '0 mL .— 0 b (St/00 M (0.125M)(X ML) ' (671. m X I: 40! 0 MA L e. (5 pts) What is the pH of the solution at the equivalence point in the above titration? ,7 Ans.pH = ’0 O f. (8 pts) What is the molarity of K+ ions after addition of 35.0 mL 0.125 M HCl solution to 45.0 mL of a 0.100 M KOH solution? A Show method. ‘ Ans. [K+] = 01 Ob é3M , i- ammmo M> : WK ,2 ” + Lil‘s—x/o We K 3 K M 0.020 L. page 3 Name g 3. (33 points total) a. (5 pts) What is the pH of a 0.100 M solution of NaCl in distilled water which has been kept under nitrogen (to avoid contact with air) ? Ans. pH = jZ¢00 Give reasoning. 4— ’ . $04 Ma (41)) M Ce 4% 441—» WM 4W 2% b. (10 pts) What is the pH of a 0.100 M solution of NH4Cl in distilled water? 4/ 4)., Show method. Ans. pH = ' X X 4» '4' + m we New [”@][’é°J=A/:Kv ,. a” f to V b [ix/o Ol/OO’X c. (8 pts) What is the [H"] of a solution 1.00 M solution of ammonia that also contains 0.500 M of NH4Cl? Show method. Ans. [H+] = Z 7x 10-10 mol/L 7‘ ' ~§ ,V/éhréo : A///,,+0H [‘(b;[8X/0 Ava—y 0,5001% )5 . , ,3” , X (0n50°+x> ‘ /Xx/OP‘{- XI ‘5 :- D.é>‘/0 : [0H] .w~7c ‘ ' (/ l + W ’7 H : ’0/3.éx(o" ; £127X’U d.(10pts) Give a Lewis structure for HClO3 in which the formal charge on the Cl atom is 0. How many electrons are there in the valence shell of the Cl atom? # HClO3 0’ No. of electrons in the valence shell of Cl: l 7/ Give the appropriate Lewis structure(s) for the [C103] anion in which the formal charge on the Cl atom is 0. [C103'] '- 26 16 a?! {I I CL «> C,Q\I <—-—> 'qu r I I! *0, s I, v v I O' 'o ' :0 '01 ‘ 2 page 4 Name (244M («(334 4. (34 points total) a. (5 pts) Briefly explain why bond dissociation energy is generally observed to decrease going down a column in the periodic table, as for example for the hydrogen halides (values in kJmol"): H-F (543) > H-Cl (419) > H—Br (354) > H-I (287). GAWMW C“ ‘7 5"” FJ‘QQEBY‘HI’ W b. (5 pts) Briefly explain why the bond dissociation energy for F2 is anomalously m in the following series (values in kJmol"): F2 (146), C12 (230), Br2 (181), I2 (139). I c. (6 pts) The elemental form of nitrogen is N2 whereas that for phosphorus is P4. Write the Lewis structures for each. ’I __ ’ P :N’shl' d. (8 pts) Referring to the Tables of bond dissociation energy, estimate the energy change accompanying the transformation of diatomic N2 into a hypothetical tetrahedral N4, both in the gas phase. 2N2 = N4 Ans. 4'38?) kJmol" Show method ' F, Maytag) a + m ki ’4 (MN) + M7313 -4063) "If 1N1 e. (5 pts) Briefly explain why hypochlorous acid, HOCl is stronger than hypoiodous acid, HOI. f. (5 pts) Briefly explain why acetic acid, CH3C(O)OH is weaker than formic acid, HC(O)OH. page 5 Name W kg 4 5. (33 points total) a. (8 pts) What is the oxidation number of S in sulfurous acid, H2803 ? Ans. +4 What is the oxidation number of Cr in potassium dichromate, K2Cr207 ? Ans. 4‘ c b. (15 pts) Draw the Lewis structure pertaining to each the following molecules providing a word or phrase to describe the shape (geometry). Also, state whether the molecule is polar or non polar and give the hybridization of the central atom for each. H2803 SF4 draw the Lewis structure draw the Lewis structure " +— ‘r 5 F; .. , .b/ \079” , SIM?" 'I -' '-.‘u+ 0%: : F." .- Shape—Mm I (shape Mrébuf‘éW) ,__f__ 4&— polar or on-polar polar or non-polar hybridization of the 3 hybridization of the sulfur atom 32 sulfur atom S Fad. —_._———__———___——_———_.__._—._____—.___—..———___——————___._———____.———_____—— ——_———_—————_———_————_————___—____————__——————————————_—_———-———_———— d. (4 pts) NiO is a basic oxide. Write a balanced chemical reaction to illustrate this property. . Alf 0 4» (viz/O »' NE (04"); e. (6 pts) BiZO3 is an amphoteric oxide. Write two separate balanced equations to illustrate this property. + M» ’leog +ZH = 2 8. +545) 5£}03 tZoH” = ZBJOIdOE; Page 6 Name—W 6. (33 points total) a. (12 pts) A 5.00 g sample of an organic compound containing only carbon, hydrogen, and oxygen is completely combusted to give 6.077 g of H20 and 11.88 g of C02. What is the composition of the Shoggwtgrckfompound? Ans. %c = 458’? , %H= (3.40 w x 4.2% = “4} C %o= 2/..(4 H‘l-O‘ L @1129 W00 P” M'WZCCMSWA /oo ‘/. S'JOE‘SW‘J‘ _, 64.2? W x 4.077 yo : 0.42314 * “140/ . o 0 flz/ x100 = /3,40%H 5:”;5‘WIJ” was i b. (12 pts) What is the formula of a salt containing 34.55 % Mg, 19.96 % Si, and 45.48 % O ? Show work. W I003 Sample. Ans. ngSiyOz x = 2. y: / M , Maw. . H2 3 z: ZU-31W/Me "vi/0'7, : Z [9% S«' ; gg/MS/‘V e. #35:? t 7 W :/ 237.093 /W£S1 0.7, W : HMO 2.3% ¢ may/wee ' .1. c. (9 pts) What is the oxidation number for each of the elements in CaH2 ? Ca + 2 . H Complete and balance each of the following two reactions: _ CaH2 + __H20 = Ca(0/*)L + 141 Ca0 + Z COL + #ZIO = C3(HC03)2 ***end of exam*** Eaxm Rim 5. macaw 22/2/22 oaooocaoc@€%@ooao<%&0890 smapms J0 .IaqumN O !—1 0] M 5:232: Sam 33m 5% <3 EEEEQ ...
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fianl spring 01 - CHEM 14A Final Exam sp 2001 (“’7 Mac...

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