{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

final fall 99 - Wednesday December 15 3:00 6:00 pm NAME I I...

Info iconThis preview shows pages 1–7. 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 Document Right 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 Document Right 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 Document Right Arrow Icon
Background image of page 6
Background image of page 7
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Wednesday, December 15 3:00 - 6:00 pm NAME: I I l I I I | I I | | I I I II I I I | I I I I I I I I I I II LAST STUDENT I.D.: W: 1.Please sign above. 2.Answer each question in the space provided. CHEM 14A Final Exam Fall 1999 3 .Where reasoning is requested, this should be. well organized and legible. 4.A]l answers MUST appear on respective pages. Prof. H. D. Kaesz T. A.‘ 5: Sharon Catak, Mailin Chu Chip Horton fingering your T A. 3 name to facilitate return of exam. FIRST SIGNATURE I Question I IMAM—II I I 34 I I I I 2 I 33 I I l I 3 34 I I I I_4__:__35___I:_______I I I 3 I 34 I I I I I I I g I 33 I I I I I I I IOTAL I 293 I I Two sheets containing the PERIODIC TABLE and other information will be separately distributed. ORS S To receive notification of your course grade, please submit a self—addressed postcard. IIIIIIIIIIIIII IIII||I|||IIII To pick up your final examination please leave a stamped, self-addressed manila envelope in the box outside my office, Molec. Sci. Bldg. exam will be mailed to you: v10 1 6X 11 S CI‘lt 1505, or at the Chemistry Receptionist, Young 3034, and the . «JL «M- page 1 Name aw l. (34 points total) A 1.06 M solution is prepared by dissolving 362.8 g of sucrose, CquzO“, in enough water to make 1.00 L of solution. The density of this solution is found to be 1.14 g/mL. a. (8 pts) What is % by mass of sucrose in this solution? V Show method. Ans. % by mass of sucrose: 3’ '3 ’ b. (8 pts) What is the molality of the solution? Show method. Ans. /- 5 Q m (molal) c. (8 pts) What volume of a 1.06 M solution of sucrose must be added to a sufficient quantity of water to make 250 mL of a 0.500 M solution? Show method. Ans. H7. ‘7 mL of 1.06 M d. (4 pts) Do you expect a solution of sucrose in distilled water to exhibit electrical conductivity (using a light bulb as the indicator)? Give reasoning. yes or no e. (6 pts) Write a balanced equation for the complete combustion of sucrose. . 50L W I‘ page 2 Name W 9,122“ 2. (33 points total) a. (6 pts) For the gas phase reaction PCl5 = PCl3 + C12, K13 = 78.3 at 250 0C. What is the value of K1) for the reverse reaction: PCl3 + Cl2 = PCl5 at 250 0C? '7— Show method. Ans. K13 = /« 23 x ID at 250 °C b. (8 pts) For the reaction PCl5 = PCl3 + C12, Kp = 78.3 at 250 OC, what is the value of KC at 250 OC? Show method. Ans. Kc: I'S’Z at 250°C c. (8 pts) Given a mixture of PC15, PCl3 , and C12 that is at equilibrium, circle one of the following two transformations which will occur if the system is compressed into a smaller volume while equilibrium is maintained. Give reasoning. (A) Some of the PC13 and some of the C12 or (B) Some of the PC15 must decompose must combine to give PCls, into PC13 and C12. (1. (5 pts) A gas mixture consists initially of 0.100 atm PC15 and 5.0 x 10‘2 atm each of PC13 and C12 at 250 0C. Show that the system is NOT at equilibrium. 6. (6 pts) For the gas mixture described in part d, circle one of the following two transformations which must occur for the system to reach equilibrium. Give reasoning. (A) Some of the PC13 and some of the C12 or (B) Some of the PC15 must decompose must combine to give PC15, into PC13 and C12. page 3 Name ________Mfl'_7 3. (34 points total) a. (5 pts) BaO is a basic oxide. Write a balanced chemical reaction to illustrate this chemical property. b.(8 pts) A1203 is an amphoteric oxide. Write two separate balanced equations to illustrate this chemical property. 0. (5 pts) Ethylamine, CH3CH2NH2, is a base. Write the chemical formula of its conjugate acid. The conjugate acid of CH3CH2NH2 is A 10.00 mL sample of potassium hydroxide, KOH, was titrated to the stoichiometric point with 18.5 mL of 0.235 M hydrochloric acid. / d.(6 pts) What is the concentration of the KOH solution? Ans. 0« '43“) M Show method e.(6 pts) What is the [H] and the pH of the original HCl solution? Ans. [H+] = O . 25( Show method pH = O . (.3 _ f. (4 pts) What is the pH of the titrated solution at the stoichiometric point? Ans. pH = ‘7' D D . Show method or reasoning. - ”4‘ . page 4 Name Wave 2:“ ‘ 4. (34 points total) a. (8 pts) A 0.100 M solution of an unknown weak acid is found to have [H*] = 1.40 x 105. What is Ka of the weak acid? Show method. Ans. Ka = [.9 I: we", b. (10 pts) A 10.0 mL portion of a solution of benzoic acid approximately 0.2 M is to be titrated with a 0.200 M solution of N aOH. What is the pH at the stoichiometric point? Ka for benzoic acid (C6H5C(O)OH) = 6.5 x 10's. Show method. Ans. pH at the stoichiometric point = Y- ‘0 c. (8 pts) What will the pH be at the mid-point injhe above titration? Show method. Ans. pH at the mid-point = 4 ’ 7 d. (8 pts) Do you expect trichloroacetic acid,CCl3 C(O)OH, to be a stronger or weaker acid than acetic acid, CH3 C(O)OH ? Ans. trichloroacetic acid is than acetic acid. Give reasoning. stronger or weaker v ' _ W Page 5 Name W m f ' 5. (34 points total) a. (4 pts) Naturally occurring rainwater is slightly acidic, pH = 5.7. Explain the source of this acidity including a balanced chemical equation in your answer. b. (8 pts) In heavily populated areas, rainwater will exhibit pH values much lower than 5 .7. Give two possible contaminants which are responsible for the higher acidity of polluted rainwater including a chemical equation showing the origin of each contaminant. c. (10 pts) Citric acid is a triprotic acid which may be symbolized as H3Cit. K“ = 7.24 x 10 4 Estimate the pH of a 0.100 M solution of disodium citrate, NazHcit. Kaz = 1.12 x 10: KI3 = 4.07 x 10 Show method. Ans. pH = (7:513 . ———_—______—_________ d. (12 pts) Provide the appropriate Lewis structure(s) for each of the following species. HZSO4 C6H5C02H (benzoic acid) .wt ~ Page 6 Name "m fig - 2W 6. (33 points total) a. (8 pts) How many moles of silver chloride are obtained per mole of each of the following compounds in solution when AgNO3 is added? Cr(H2 O)4Cl3 Cr(H2 O)3C13 mol AgCl per mol complex mol AgCl per mol complex Show reasoning. Show reasoning. b. (9 pts) Draw all the unique isomers for the complex Co(NH3)4C12 using \\ I /’ octahedral coordinates like the ones shown at the right. /Co\ I c. (8 pts) Calculate the molar solubility of AgCl using KSp (AgCl) = 1.6 x 10‘“). I S Show work. Ans. / . 7. 7 xlo M c. (8 pts) The presence of ammonia in solution will increase the molar solubility of AgCl due to the formation of the ammonia complex of the silver ion: Ag+ (aq) + 2 NH3(aq) = Ag(NH3)2+ (aq) Kf = 5.6 x 108 Write the equilibrium expression for the following reaction and calculate the equilibrium constant from information available to you on this page. AgCl (s) + 2 NH3(aq) = Ag(NH3)2+ (aq) + C1'(aq) Equilibrium K = X. ‘7‘ x I 0 expression: Mend of exam### ...
View Full Document

{[ snackBarMessage ]}