exam 2 fall 10 - CHEM 31 October 27, 2010 Exam 2 Name %...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 6
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 8
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: CHEM 31 October 27, 2010 Exam 2 Name % Lehigh user ID INSTRUCTIONS: 1. You must show your work to receive credit for problems 2—7. Organize your work so that a grader can follow your logic and written process. 2. Use the correct number of significant figures in answers to all questions on the exam. 3. If necessary, please continue your solutions on the back of the preceding page (facing you). 4. There are a total of 7 problems on 9 pages. Count the pages before you begin. 1.) Multiple Choice Questions: (3 pts each) A.) If K for a reaction is large, 1.) AH° is definitely positive. 2.) AG“ is definitely positive. .) AB” is definitely negatiVe. AG" is definitely negative. B.) Consider the following reaction at equilibrium, 2NH3 (g) = 3 H2 (g) + N2 (9 Le Chatelier’s principle predicts that the moles of H2 in the reaction container will increase with 1.) some removal of NH3 from the reaction mixture (V & T constant). it"- 2.) addition of some N2 to the reaction mixture (V & T constant).<—-=— 3.) a decrease in the total volume of the vessel (T constant). 44-— @ an increase in the total volume of the vessel (T constant). »--=,~ C.) A sealed tube containing an equilibrium mixture of N02(g) (brown) and N204(g) (colorless) is subjected to a variety of temperatures. For the equilibrium reaction shown, the values of the AH‘ZXn and AS°m are also givenm is observed in the tube with increasing temperature? ‘r p 2 N02(g) t" N20405:) ° = —58.02 kJ/mol, AS" a 476.5 J/mol - K brow 4: ® At higher temperatures, the gas in the tube has a darker brown color. 2.) At higher temperatures, the gas in the tube has a lighter brown color. 3.) The color does not change with temperature. 4.) At higher temperatures, the gas turns green. D.) The concentration of [F'] resulting from the weak acid ionization of HF is @the same as the concentration of [P11 resulting from HF ionization. 2.) less than the concentration of [HF] resulting from HP ionization. 3.) greater than the concentration of [IT] resulting from HF ionization. 4.) unrelated to the concentration of [H+] resulting from HF ionization. E.) An acidic solution has 1.) a pH < 7. 2.) a pOH > 7. 3.) more H3O+ than OH“. 6 all of the above are correct for an acidic solution. flit?" " F.) What is the approximate pH of a solution of sodium fluoride in water? ‘9 - ' ' 2:“: ' 4 OH ‘ 1‘) PH 2 7; sodium fluoride is a Simple salt. F t H 2.0 H F @pH > 7; fluoride is a weak base. 3.) pH < 7; fluoride reacts W/ water to make HF. 4.) pH 3 7; fluoride is a weak base, but produces HF in water. These neutralize one another. G.) An I-ICl solution with a pH of 3 is mixed with an equal volume of an HCl solution with a pH of 6. Which of the following is closest to the pH of the resulting mixture? @3 2.) 4 3.) 4.5 4.) 6 5.) 6 H.) Using the data in the table below, choose the stron est conjugate base: 1. F ‘ 2-)(C10)' 7 ' “raw: Kb 3. CHOZ) ‘ 4-) ((3214302)— I.) A 0.10 M solution of has a pH 4: 7.0. 1.) Nags 2.) NH4C1 J.) Your solution in the xylenol orange lab (Lab #5) was buffered at a pH of 2. Which of the following acids (along with their conjugate bases) is the best choice for making that buffer system? 1.) Formic Acid (Ka =1.3 x 10“) 2.) Oxalic. Acid (Kal = 5.9 x 10’2, K32 = 6.4 x 10-4) '3. Sulfuric Acid (K32 = 1.2. x 102) .) Tartaric Acid (Kal = 1.0 x 10'3, Kaz = 4.6 x 10'5) Problems ~— show your work: 8 pts 2.) A 25.0 mL sample of 0.723 M HCIO4 (aq) is titrated w/ a 0.273 M KOH (aq) solution. What is the pH after the addition of 66.2 mL of KOH to the acid? Reaction: + KOO” (a g ) 0.0;zSOL x .723mot and 1&0ng mr€ ‘2ch (L. (LOGGQL. X «BREW/Ha back; ; O_OI%I mfg balm (L. QCAOiI :— €¢szcLLaflCLu PENNJ— ‘ pH :10 (SA + 35‘) 12 pts 3.) Sodium benzoate (C6H5C02Na) is used as a food preservative. Calculate the pH and the concentrations of benzoatc and benzoic acid in 0.050 M sodium benzoate; Ka for benzoic acid (C6H5C02H) is 6.5 x 10'5 at 25°C. a.) Write the reaction: + Ma) C6H5C02Na(aq) + HZOM) = C; ascozH b.) Set up ICE table: I Q‘ Q? C >< E t x MED—x) A pH:$»"i'3 _.c. L x» [06H5002']= 0.0550 7 M [‘G%) [C6H5C02H]= mm“ M “(a A ‘ Bonus: 7% MD M: L0H] ma+1= 0mm : SS? pH=3H3 9 pts 4.) The following data set was collected and graphed for the aluminum + xylenol orange reaction that you studied in lab: Temperature Dependance of AG° for the complexation reaction between aluminum and xylenol orange AG" (id/moi) a» Experimental Data Linear Fit AH". 113.46? “1ch 340 350 350 370 AS": OMAB inf/L. may Temperature (K) i C. AG Calculate Keq at 298 K. “MILE/Pt st ope; AGO; (1154a 93;) ._. (293%)(‘1'Dx 2123 ii: \ inn-rt moi 0 AG :‘ -fi'J/fnd_é: C0 aim/‘4‘ Mfg M =' raw-HUME" Mid —Qm K Age-Agora-uer/HK "'36:"? m K' 1 ) 0 : Mfr— er K .04. K i '9 ._ ‘1 A O : " In K V - 6 K :2 4.51 x 10 ? 9 pts 5.) Calculate the pH of 2500 mL of a buffer that is 0.275 HPO42' and 0.22 W3". Ka for HPO42' is 4.2 x 10'13 at 25°C. a“ ., 3 _ 0 *- PHT Pta‘i’ /[a(i( ) I n Kq .. . ._ -. - “Hi pH — mars + io- 0”" 3 Draw/1 12 pts 6.) Consider the following titration data when a weak monoprotic acid was titrated with a strong base: Titration of a weak acid with a strong base 0 5 1O 1 5 20 25 3O 35 40 Volume of 0.100 M NaOH (mL) added Clearly mark on the titration curve (label the points A—F), the points that correspond to the following: A.) the equivalence point of the titration. " nbo M; pH ? . O B.) the region with maximum buffering capacity. 0-) PH : PKa V2, wan to libmcdluwce. D.) pH depends only on [weak acid]. [ o .0 mL brace) E.) pH depends only on [conjugate base]. @ QfiWU point F.) pH depends only on amount of excess strong base added. 20 pts 7.) AA 100.0 mL sample of 0.100 M ammonia (K43 : 1.8 x 105) is titrated w/ 0.250 M nitric acid. Calculate the pH after addition of each of the following volumes of acid: (a) 0.0 mL, (13) 20.0 mL, (0) 40.0 mL, (d) 60.0 mL. Make sure your calculation work is easy to follow. (a) Ammonia+0.0mLacid addedz‘ OH _ A / f5” NHNM} f H200) T“: NW+rk7b + )6 ""2) Kb: “6 “O I o.[oolv‘\ ' ‘ Q” ' c; fix E” (04604) I re 0H e K : (XXX) : l-QP‘LMYD P 330’ b (0%“) 'PH : 1m: 335mm Xa 1 l3 “0‘9 " xcei (0400) x t .0013 H 2 font] A '+2o.0 L 'dadd d: _ (b) mmoma :11 ac: e “A M + OtfiDGOLX momma: i.oloorni’é . Na ' NIL/3M!” + H (pi) ‘— (‘IL£) 1L 5 ~ ‘ G.“ . 3 are ‘ “HA. I t O i we cog!“ Q, ‘ 0.0).ooLx mama)“; 00 #0 mg W C, -—,oo€—;mol "‘,005{3mel 11-0059MO‘Q IL m a :3 14+ I - 3’ w .qu E: W'fiflK—fl .uI'LOL kiwi Ka‘k'b L1 JD ‘ A J 51,,on K1leO :- . a 1. 10(Eba‘“~)/@Ud]) a . I W 11;?— j mus—b PH :: (115+ {03 [04.1. H .041 M {(1 WW? fa} i¢®M¢fihflkfl IDOEZIWrti "‘*"—"‘r " Continuation of problem 7 I (EC/LC . (c) Ammonja+ 40.0 mL acid added: igqog L R {750 mo} ; eeloqme ,f -5‘ .‘fl‘ - NH} ( 51‘ ) + H” - I gmoomfl aO!ODMol 9/ C, famomuk “.0500 ml +,0looml E 3’ 15’ g OWOmoL ~ (d) Ammonia + 60.0 mL acid added: game) mafl Alsz 9- 86500:. x; .‘a‘mmwé’ : fame “We “WA IL aOa'E‘C’ alt/dc? m f ,5)er mra A“; W f’fla-fi atodci 131.. Lug/L33 £0650 ; swag M Oeffio Lu fatal ...
View Full Document

This note was uploaded on 10/03/2011 for the course CHEM 31 taught by Professor Roberts during the Fall '10 term at Lehigh University .

Page1 / 8

exam 2 fall 10 - CHEM 31 October 27, 2010 Exam 2 Name %...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online