Fall 2013 CCBC-Catonsville (Mon 11/25/13) Use your time wisely. Do not get stuck on one question. Except for the multiple choice questions (#1 through 18), NO CREDIT WILL BE GIVEN UNLESS WORK IS SHOWN CLEARLY. UNITS MUST BE INCLUDED IN YOUR SETUPS. As usual, watch your units and significant figures. TOTAL YOUR SCORE SCORE POSSIBLE page 1 24 page 2 24 page 3 22 page 4 12 page 5 10 page 6 8 TOTAL 100 Bonus p.6 6 Adjusted Total Current Course Average (based on 4 Exams, 18 quizzes, 14 Wiley HW, 7 paper HW) = Course Average is calculated based on this formula to give you a rough estimate of your current standing: 0.85 x Av Exams + 0.15% x (Av Quizzes, Wiley and paper HW) EQUATIONS [base] ph = pk a+log or poh = pk b + log [acid] RT E = E lnq G = RT lnk nf at 25 C E = E 0.0592 logq n K a at 25 C HIO 3 1.7 x 10 1 HCO 2 H 1.8 x 10 4 HNO 2 7.1 x 10 4 HF 6.8 x 10 4 HOCN 3.5 x 10 4 HC 2 H 3 O 2 1.8 x 10 5 HC 4 H 7 O 2 1.52 x 10 5 HClO 3.0 x 10 8 HCN 6.2 x 10 10 H 2 O 2 1.8 x 10 12 [acid] [base] K b at 25 C C 4 H 9 NH 2 5.9 x 10 4 CH 3 NH 2 4.4 x 10 4 NH 3 1.8 x 10 5 N 2 H 4 9.6 x 10 7 C 6 H 5 NH 2 4.1 x 10 10 CONSTANTS R = 8.314 J.mol 1 K 1 R = 0.0821 L atm mol 1 K 1 R H = 2.18x10 18 J 1 F = 96,500 C mol 91 1 F = 96,500 J V 1 mol 1 N A = 6.022x10 23 mol 1 h = 6.626x10 34 J s c = 2.998x10 8 m s 1 K w = (@ 25 C) = 1.00x10 14 0 C = 273.15 K K sp at 25 C AgCl 1.8 x 10 10 PbSO 4 6.3 x 10 7 PbCl 2 1.7 x 10 5 Al(OH) 3 3.0 x 10 34 AgI 8.3x10 17 Ca(OH) 2 6.5 x 10 6 Mg(OH) 2 7.1 x 10 12 MgCO 3 4.5 x 10 9 Ag 2 SO 4 1.5x10 5 BaCO 3 5.0 x 10 9
Fall 2013 Page 1 Multiple Choice (3 pts each): Circle the ONE best answer. 1. Which pair would you use in order to produce a buffer solution with ph = 4.8? A. HCO 2 H/HCO 2 B. HC 4 H 7 O 2 / C 4 H 7 O 2 C. HCN/CN + D. NH 3 /NH 4 2. Which of the following promotes spontaneity in a chemical reaction? A. ΔG = 0 B. ΔE < 0 C. ΔG > 0 D. ΔH > 0 E. ΔS > 0 3. What is the ph of a buffer solution prepared by taking 0.250 moles of HC 4 H 7 O 2 and 0.400 moles of NaC 4 H 7 O 2 in sufficient water to make 1.400 liters of solution? A. 1.20 B. 5.02 C. 4.62 D. none of the above 4. Which species has a highest concentration in an aqueous solution of 0.40 M HF solution? HF has a K a value of 6.8x10 4. A. HF B. F C. H 3 O + D. OH 5. What type of titration curve is shown below? A. titration of strong acid (in flask) with strong base (in buret) B. weak acid being titrated with strong base C. strong base being titrated with strong acid D. weak base being titrated with strong acid 6. Which of the following is the best choice to be added to 0.40 mole of NH 3 to create a buffer solution of ph = 9.26? A. 0.40 mole HC 2 H 3 O 2 B. 0.40 mole NaC 2 H 3 O 2 C. 0.40 molenh 4 Cl D. 0.40 mol NaOH 7. Which of the following is least soluble in water according to solubility rules? A. Ba(ClO 3 ) 2 B. Pb(C 2 H 3 O 2 ) 2 C. FeCO 3 D. Sr(OH) 2 E. K 3 PO 4 8. Which has more effect on the solubility of PbCl 2 in water? A. adding 0.1 M NaCl B. adding 0.1 M MgCl 2 C. neither D. both have the same effect.
Fall 2013 Page 2 9. Will a precipitate form when 20.0 ml of 1.8x10 3 M Pb(NO 3 ) 2 is added to 30.0 ml of 5.0 x 10 4 M Na 2 SO 4? A. yes B. no 10. In an experiment it is planned to add 300 ml of 2.0x10 5 M AgNO 3 to 200 ml of 2.5 x 10 9 M NaI. Will a precipitate form? What is the precipitate? A. Yes, the precipitate is AgNO 3 (s). B. Yes, the precipitate is NaNO 3 (s). C. Yes, the precipitate is NaI (s). D. Yes, the precipitate is AgI (s). E. No precipitate will be formed. 11. How will the solubility of BaCO 3 be affected by lowering the ph? A. It will become more soluble. B. It will become less soluble. C. Its solubility is unaffected by ph. 12. If we were to add dropwise, an aqueous solution of NaOH to a solution containing equimolar Ca(NO 3 ) 2 and Mg(NO 3 ) 2 and a precipitate begins to form, which is likely to be the precipitate? A. Ca(OH) 2 B. Mg(OH) 2 13. Which should have the lowest standard entropy? A. Cl 2 (g) B. I 2 (s) C. Br 2 (l) D. N 2 (g) E. He (g) 14. Which process is accompanied by a positive value for the entropy change of the system? A. CH 4 (g) + H 2 O (l) CO (g) + 3H 2 (g) B. BaO (s) + CO 2 (g) BaCO 3 (s) C. Na 2 CO 3 (s) + CO 2 (g) + H 2 O (l) 2NaHCO 3 (s) D. ZnS (s) + 3/2 O 2 (g) ZnO (s) + SO 2 (g) E. N 2 (g) + 3H 2 (g) 2NH 3 (g) 15. For the reaction 2NO (g) + O 2 (g) 2NO 2 (g), H = 113.1 kj/mol and S = 145.3 J/K mol. Which of these statements is true? A. The reaction is spontaneous at all temperatures. B. The reaction is only spontaneous at low temperatures. C. The reaction is only spontaneous at high temperatures. D. The reaction is at equilibrium at 25 C under standard conditions. E. G becomes more favorable as temperature increases. 16. For a reaction with K = 6.3, is G positive or negative? A. positive B. negative C. neither as it is zero
Fall 2013 Page 3 17. Calculate the value of E cell for the cell with the reaction: 2Cr 2+ (aq) + 3Cl 2 (g) 2Cr 3+ (aq) + 6Cl (aq) Cr 3+ (aq) + e Cr 2+ E = 0.40V Cl 2 (g) + 2e 2Cl E = +1.36V A. 0.96 V B. +0.96 V C. +1.76 V D. 1.76 V E. +0.98 V 18. According to the reduction potentials, which is the better reducing agent? A. Sn 2+ B. Ni 2+ C. Sn D. Ni END OF MULTIPLE CHOICE SECTION 19. (8 pts) K form of the complex ion, HgCl 4 2 is 1.1x10 13. a) Write the chemical equation corresponding to this equilibrium constant. b) Write the equilibrium expression corresponding to this equilibrium constant. K = c) What is the value of K inst for this ion? Show your work. Ans. d) Write the equilibrium expression corresponding to this K inst. K = 20. (8 pts) You have 500.0 ml of a buffer solution containing 0.35 M acetic acid and 0.24 M sodium acetate. What is the ph of the solution after 23.5 ml of 1.12 M NaOH solution is added?
Fall 2013 Page 4 21. (6 pts) Calculate the molar solubility of Ag 2 SO 4 in a 0.143 M Na 2 SO 4 solution. SHOW YOUR WORK! Ans. 22. (6 pts) Given the data for 25 C: H f (kj mol 1 ) S (J mol 1 K 1 ) C 2 H 6 (g) 84.5 +229.5 O 2 (g) +205 CO 2 (g) 394.0 +213.6 H 2 O (l) 286 +69.96 WATCH YOUR SIG. FIG. AND UNITS! a) Calculate the standard free energy change for the reaction at 25.0 C: 2C 2 H 6 (g) + 7O 2 (g) 4CO 2 (g) + 6H 2 O (l) Ans. b) According to your answer, is the reaction expected to be spontaneous? Circle one: Yes or No
Fall 2013 Page 5 23. (6 pts) Balance the following equation for the reaction taking place under acidic conditions: Work must be shown clearly. I 2 + HNO 3 HIO 3 + NO 2 24. (4 pts) A galvanic cell consists of a Cd electrode and a Zn electrode. Reduction occurs in the cadmium half-cell. Give the standard cell notation for this cell: Which direction will the electrons flow? (Circle one) A. from the Cd electrode to the Zn electrode B. from the Zn electrode to the Cd electrode
Fall 2013 Page 6 25. (8 pts) Consider the reaction H 2 C 2 O 4 + 2 HNO 2 2 CO 2 + 2NO + 2 H 2 O a) Which element is undergoing oxidation? Ans. b) Its oxidation number is changing from to. c) Write the two balanced half reactions: d) What is the total number of electrons being transferred as shown in the equation above? Ans. e) Draw an arrow in the equation shown above to show exactly from where and to where the electrons are transferred. f) Which is the oxidizing agent? Ans. Bonus Points: (1 pts) Make sure your name is on every page, front and back. (3 pts) Consider the reaction MnO 4 + 5Ag + 8 H + Mn 2+ + 5 Ag + + 4 H 2 O. If we were to use the equation the Nernst equation shown on the front page, what is the value of n? Ans. n = (2 pts) What is the formula of the gas formed when we boil C 6 H 14? Ans.