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Land exam2 97 key

Land exam2 97 key - 904.0?“ 54m Key I Part 1 Mult Choice...

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Unformatted text preview: 904.0,?“ 54m] Key I Part 1: Mult. Choice, Concepts and Short Calc.'s, 110 pts - No Partial Credit 1. (30 pts total) Consider the following reaction allowed to come to equilibrium: 2A(g) + 2B(l) 2‘3- 2C(g) + 3D(g) Aern= -105 kJ 0 mol'1 If equilibrium is perturbed by the following changes, what will be the effect on the indicated quantity when equilibrium is reestablished? Change in conditions: Effect on Rxn: Increase Decrease No Change (a) If more C(g) is added, what is the effect on the concentration of A(g) present? 2g (b) If more B0) is added, what is the effect on the concentration of A(g) present? X (c) If more C(g) is added, what is the effect X on the value of the reaction quotient, Q? (d) If more C(g) is added, what is the effect on the value of K? X (e) If the volume of the reaction vessel is decreased, what is the effect on the X concentration of D(g) present? (f) If the temperature is decreased, what is the effect on the value of K? X 2.(10 pts) An analysis of a reaction mixture showed that it had the composition: [N2] = 0.7 M [H2] = 1.4 M [NH3] = .3 M Given that the reaction: N2(g) + 3H2(g) ? 2NH3(g) has Kc = 0.278 at a particular temperature, what will be true about the concentrations at equilibrium? A. The concentrations will not change; the reaction is already at equilibrium. B. The concentrations of both N2 and NH3 will increase. @he concentrations of N2 and H2 will decrease while NH3 increases. D. The concentrations of N2 and H2 will increase while NH3 decreases B. All concentrations will decrease slightly. Q - [6, 3); C. 3.(25 pts) Fill in the following table: (No credit for incorrect formulae or charges.) conjugate acid conjugate base lkflg+ NH3 Mali 3 4.(10 pts) What is the pH when equal molar quantities of NH3 and HNO3 are combined? 5 7‘” . . A. between 7.1 and 13 ”j 5“ 4 Crap. Q, C D 4 B. between 1 and 6.9 f” 7 C. equal to the value of the pKa for HNO3 D. equal to 7 E. unknown 5.(10 Pts) 3.(2 pts) Which of the following weak acids has the strongest conjugate base? 3) Idea/{eff 4:129 A. HC2H302 (Ka = 1.7 x 10-5 M) B. HCH02 (Ka = 1.8 x 10-4 M) c. HF (Ka = 6.8 x 10-4 M) D. HClO (Ka = 3.0 x 10-8 M) E. HCN (Ka = 4.8 x 10- ' M) 6.(10 pts) Which of the following salts gives an acidic aqueous solution? A.KNO3 Mafia Acidic 5002. CW4 altu' kg; “we @3 ”a “my 2"“ + nail/4 in: C. NazSO4 1n 4; c D. NaHS “5:4 E. LiF basic 7.(15 pts) The pH of a 0.20 M HClO aqueous solution is 4.11. The value of K3 for HClO is A. 1.6x10-10 B.1.6x10-11 c.6.3x10-5 E.2.5x10-10 mm + A20 2:? 46* + C/a‘ 11/79 0, 20 M . 0 0 E; azo~x >4 X 962M 7H 9: {mo Xr/o'q'u 2 5537/11/55. ~9- .2 Ki : (7'J/V‘IO j :— 3/&/*/0‘8 0,2 ~ }.¥(-¥/o“ 3‘ Part II: Word problems, 4 questions, 140 pts - show all work for partial credit! 8.(30 pts total) Calculate the molar mass of an unknown aqueous acid (HA) if it takes 40 mL of 0.1500 M NaOH(aq) to reach the equivalence point when 0.25 g of the acid is dissolved in 20.0 mL of solution. 4‘5, ziuw. do?! mo/«s acin :: ma/rs Last *3 nip/(5' baée -‘~' 0:040 L X d,l5‘00%’——(:‘4h 9.(40 pts total) Consider the following solutions with nitrous acid: (a)(10 pts) Estimate the pH of a solution containing 0.3M HN02 (Ka = 4.3*10'4)? flueu #10 2:“ #90‘ 4 w; 23:! a; , o @ awn/oh -x «X 4-K _____.———-———~_———————————————- find 0.34 x V K - 60k) : 46%: IO -4 4" 0,5-x - ~-? “6mm x«o,3 :2) X2: (4,39; )0 ”)(0’3) ; X: /v/y-¥/0 A solution is made by combining 100 mL of a 0.3M solution of nitrous acid with 100 mL of a 0.2M solution of sodium nitrite, NaN 02. (b)(10 pts) What are the four major species present in this solution? 1. [‘14. + 2. 120.; ' 3. AW 0, 4. #2 0 (c)(20 pts) What is the pH of the combined solution? um t #20 :2 2M + w; 1;:7‘ 0:3” ‘ O DIR/’7 allow ”X 4-K +A’ W 0:3'x x 0,244! K; NM“) dgfamc x<<a2 10.(40 pts total) Calculate the pH for the following cases in the titration of 50.0 mL of 0.1M CH3COOH (Ka=1.8*10'5) with 0.2M NaOH solution: (a)(10 pts) before addition of NaOH(aq) + _ 2 #A + #2 :: l/zo t I) X mm” rm 0» I ' 0 0 a” A --X +x in? 4557““: Y<<0” _—_————~_________.—————————-————'—'_—'———— 2: [I $’~¥/ . 6 Anal 0J~X X y X 0v--3 (b)(10 pts) after addition of 12.50 mL NaOH(aq) (54“,?ch "Mo/(S ”4.0”“ .- )2, SML X 0! 2", :- 2’ 5 ”“0, b4 5‘ hind/05‘ IMO : 50 ML .t 0, [m = 5,& Mluo/ acme (lain/.1321 ):41/1 way pn‘nf’. f”: PKA : ‘7" 79’ (C)(10 pts) after addition of 25.00 mL NaOH(aq) g I!“ MW“ 94:4: 25h1uo.2m= 5,050.”) 454 away/e; 140%: fiflmm/ 4022 - 9~I5h1u'am/».‘c I" X. fiycc/‘ec 40% ”43A ) (A0) n .- /o—’v = - ’0 A' + $20 ? ”A + 0H )6" [iii/0'7 9 964/0 [\i, 500“, O O 0 22x ”ml- +x 4 x x 7- . )0 : 515K420 :1 .067»! x K ’04? - K (d)( 10 pts) after addition of 30.00 mL of NaOH(aq) mac/“S45“ ( mm! kid: 5 Larec } MMO/ Lac 90 )n L [51¢ r/JI-tt/o'2 900 >149) 39/7,: LQJ 1‘ LXI/5 Ital: .C, 4. 11. (30 Pts) Kc for the reaction 2 Nine): N2<g> + 3 H2<g> is 0.395 at a particular temperature. A 19 g sample of NH3 is placed in a 2.00 L reaction flask and allowed to come to equilibrium. What are the equilibrium concentrations of NH3(g), N2(g), and H2(g)? ”wt/3 g ’2 >‘ 3 1‘12. Im‘I‘ /72 0 0 2,01, A - 2x +X +3)! E? 1-33- -—.?)L X BX 210‘- ...
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