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cem152-ss08-key-exam3A - Name CEM 152 ssos PID ibk(34th red...

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Unformatted text preview: Name: . CEM 152 ssos PID: ibk / (34th red Exam 3A—March 19, 2008 Answer each question in the space provided. Clearly mark your final answer. Show all work for full credit. 1. A 0.025 M solution of a certain weak acid has a pH = 4.41. Determine the acid dissociation constant (Ka) of the weak acid. —— —‘-I~LH _ <9 HA e—a H++A' xzimjgio Wisp =3.Fn<)o M . /— o -—S‘ SW 0.013 +7§ 4: [glifpflp ammo {a I” 47‘ _ - flm: 0.0}‘1fim CH ERA]: M” We?” .CC‘QJ 0,095*7< S) _ ——)‘ _ K s m“) [IQ-(3‘ (3.261H8Y)L?‘861“0 im a ‘ CHAD (Mum h“ 2. (10 pts) In lecture, the equilibrium dissociation N204 (g) <—> 2N0; (g) was observed to shift to the left when the temperature decreased. Select the relation below that best explains the change in the equilibrium constant with temperature, and briefly justify your answer. @Arrhenius equation \ la f Y (A; b B) Clausius-Clapeyron equation B 0k“ M0“ W” OMS ”A v‘ C) Freezing-point Depression equation 0 L r “Lg é'Mpl—mv'il' 3 D) van der Waals equation FQ/RT waive. conrW/‘lc ”k e 3. (12 pts) For the exothermic equilibrium process 2N02 (g) H N204 (g), determine how each statement will affect the equilibrium condition, using the words SHIFT LEFT, SHIFT RIGHT, or NO CHANGE. N a. Add inert Xe(g) to the reaction vessel. b. Increase the temperature of the reaction vessel. 0. Increase the volume of the reaction vessel. d. Add a homogeneous catalyst to the reaction vessel ." N Name: _ CEM 152 $308 PID: \Aej _ (3d Am m at Exam 3A — March 19, 2008 4. (12 pts) The equilibrium reaction 2802(g) + 02(g) H 2803(g) has a value Kp = 0.241 at 150 °C. An empty reaction vessel is initially charged with all three gases to the same partial pressure P = 0.025 atrn. Calculate the reaction quotient and determine which way the reaction will proceed to achieve equilibrium. 2303+0}C—-3 3303 $4 0.0.x)“ so}? 0035“ 1 Q2. ijgog _(0~0 , . t . ‘ : (+0 M” 1 .oar 2 u. 5‘ LOWS) 0 Pfoz POL C ) KP: 0.3»‘H < ‘4on \ (eff? i—o S0‘ALD, Q7Lp ) r-efiC/‘LM OYDCRCI’U h \ aohev€ QfiV\l\LV‘Vv/V\ 5. ( 12 pts) Consider the following statements regarding acids and bases, and determine whether each statement is true or false. T a. The conjugate base of a strong acid is a weak base. F— b. A substance that is an electron pair receptor is an Arrhenius acid c. Strong bases completely dissociate in water at low molal concentrations. T d. Hydro gen-containing molecules that do not transfer protons to water are the weakest acids. 6. (10 pts) At normal body temperature (37 °C), the pH of blood is 7.40. Given that Kw = 2.4 x 10'14 at this temperature, what is the pOH of blood? Hero e; 9% Ma“ \szltqflfi KN; [Ply] LOWS '10“ :MO gfiS/‘Ho $4 CHHC—w :ro : ano’ M 2 (’5 figr \o'g) (C0 0.3) C9 pf] : (0.0)— 7400' 7M 7 (301* :..—— L03 ((oflQ—fCO Name: _ CEM 152 ssos PID: KW . Gama/«WA Exam3A—Marchl9, 2008 7. (12 pts) Determine the pH of a buffer solution prepared from 0.050 M acetic acid (HC2H302), a weak acid with Ka = 1.8 x 10‘s, and 0.012 M sodium acetate (N aC2H302). Please state any assumptions made in determining the pH. HCLH30L CA H’} + (1‘4307: +76 +7< W {Kali 0—05‘0 " P‘ X 0 «on +>< K .1}th (0’; CH HJCCZH (321)-W {/6105}qu .l—Q (LOSWK 0M9] a C ”(1th a] (gravy—x3 otoilM 0.037. ,— it: —( YXDP) MW 5:— (0031))?“ $2 CH+3313XlO MP 09% 8. (12 pts) A generic curve for the titration of a weak acid by strong base is the right. Clearly indicate whether each of the following statements about the titration curve is TRUE or FALSE. F; a. The pH of the solution at “E” is determined by the amount of excess weak acid. "1" b. The solution at “B” acts as a buffer. c. The concentrations of weak acid and strong F base in solution are equal at “C”. F d. The pH at “D” is always 7, regardless of the chemical fom1 of the weak acid. I i'olurne of NaOH added (rm-T.) 9. (10 pts) Which of the three curves in the plot on the right represents the effect of concentration on the percent ionization of a weak acid? t A ’ Explain, in qualitative terms, why the curve you if? chose has the shape it does. 3 ~ L MD (3 8 B (Z) WMILWhQM: 0+0} V E \ 2h o L g M Dial 1‘ ) MW” "‘ . 5: 0 31mm (Q her/WORKS (VClQa'NC‘D) Car/6% vii. Acid Concentration —> ...
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