OKANAGAN UNIVERSITY COLLEGE FINAL EXAMINATION CHEMISTRY 121

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1 Name (Print) Surname Given Names Student Number Centre OKANAGAN UNIVERSITY COLLEGE FINAL EXAMINATION CHEMISTRY 2 Professor: Nigel Eggers, Renee Van Poppelen, Stephen McNeil April 5, 2004 Duration: 3 hours This paper contains pages numbered to 23 THE DATA SHEET, Page 23, MAY BE CAREFULLY REMOVED FROM THE EXAM READ INSTRUCTIONS CAREFULLY BEFORE COMMENCING EXAM Exam booklets are not required SHOW ALL WORK Section A Answer ALL Questions Section B Answer 3 out of the 5 Questions Circle the questions in Section B that you have answered Include the appropriate units in your answers. QUESTION VALUE MARK SECTION A Answer ALL Questions Total Section A 70 SECTION B 0 Answer 3 of Questions Total Section B 30 TOTAL 00

2 Page 2 COMPULSARY SECTION A. A first order reaction has a rate constant of.368 min -. a) How long will it take for the reactant to reach 3.2% of it s original value? b) What is the t ½ of the reaction? [4 marks] 2. If a reaction has k = 8.76 x 0-2 s - at 25 C and an activation energy of 67.4 kj.mol -, what will be the value of the rate constant at 50 C? [3 marks]

3 3. Calculate K p for the reaction below at 300 C N 2 (g) + 3 H 2 (g) 2 NH 3 (g) K c = 9.5 at 300 C Page 3 [2 marks] 4. Carbon monoxide, hydrogen, methane and water were placed in a reaction vessel at 800 K. The chemical reaction is CO(g) + 3 H 2 (g) CH 4 (g) + H 2 O(g) and the initial partial pressures were: CO.05 atm, H 2.00 atm, CH atm and H 2 O.75 atm. After the reaction had reached equilibrium the partial pressure of H 2 O was 2.00 atm. Calculate K p at 800 K. [3 marks]

4 Page 4 5. Consider the system [2 marks] 4 NH 3 (g) + 3 O 2 (g) 2 N 2 (g) + 6 H 2 O(l) H = -530 kj How will the amount of ammonia at equilibrium be affected by (use the terms: increase, decrease, no change) a) removing oxygen gas? b) adding helium gas? c) expanding the volume of the container at constant temperature? d) increasing the temperature? 6. a) Describe the following terms and give an example for each. [2 marks] i) Brønsted acid ii) Lewis base

5 Page 5 7. Fill in the blanks in the following table: [2 marks] Conjugate base of H 2 PO 4 Conjugate acid of HPO 4 2 Conjugate acid of CH 3 NH 2 Conjugate base of HNO 3 8. Calculate the ph of the following: [4 marks] a) 0.7 M hydrocyanic acid (HCN ). K a (HCN ) 6.2 x 0-0 b) M ammonium chloride, NH 4 Cl. K b (NH 3 ).80 x 0-5

6 9. The ph of a 0.50 M aqueous solution of hypochlorous acid (HOCl) is found to be Calculate K a for hypochlorous acid. Page 6 [3 marks] 0. Find the ph of a buffer prepared by mixing ml of M NaCN with ml of 0.50 M HCN. K a (HCN) 4.00 x 0-0 [3 marks]

7 . Calculate the molar solubility of silver chromate in 0.50 M K 2 CrO 4 (aq) at 0 C. The solubility product, K sp, of Ag 2 CrO 4 is 3.00 x 0 3 at 0 C. Page 7 [3 marks] 2. Calculate the enthalpy for the fourth reaction below. [3 marks] () 3 CH 4 (g) + 3 H 2 O(g) 9 H 2 (g) + 3 CO(g) H = 68.3 kj (2) ½ CO(g) + ½ H 2 O(g) ½ CO 2 (g) + ½ H 2 (g) H = 20.6 kj (3) 2 C(s) + 4 H 2 O(g) 2 CO 2 (g) + 4 H 2 (g) H = 80.2 kj C(s) + 2 H 2 (g) CH 4 (g) H =?

8 Page 8 3. From the thermodynamic data at 25 C provided for the reaction: [3 marks] a) Calculate G rxn at 25 C. 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) Thermodynamic function SO 2 (g) O 2 (g) SO 3 (g) H f (kj.mol - ) S (J.mol -.K - ) b) Is this reaction spontaneous or nonspontaneous under standard conditions at 25 C? Explain. [ mark] c) Calculate the equilibrium constant at 25 C. [3 marks] d) Calculate the total entropy change of the universe for this reaction at 25 C [ mark]

9 Page 9 4. Give the IUPAC name (or an acceptable common name) for the following compounds. [5 marks] O H O OH OH 5. Draw structures for each of the following compounds [2 marks] 2-pentanone propyl ethanoate

10 Page 0 6. For the following two molecules: [2 marks] a) list the order of priority of the substituents on the stereogenic carbon b) specify if the stereogenic carbon is R or S COOH O H 3 C H NH 2 7. Circle each of the stereogenic carbons in the two molecules below, and write the total number of stereogenic carbons underneath each molecule. [2 marks] OH OH O OH O OH OH CH 2 OH 8. For each pair of reactants, draw the products showing all non-zero formal charges and relevant lone pairs. [3 marks] CH 3 CH 2 OH + H I HO + CH 3 Cl Br

11 Page 9. Draw the transition state for the following S N 2 reaction. Indicate bonds which are forming and those which are breaking by dashed lines. Show all partial charges on appropriate atoms. [2 marks] HS + CH 3 Br 20. For each reaction, show the curly arrows, relevant lone pairs and all formal charges for each step in the mechanism, draw the intermediates and the final product. [4 marks] Br CH 3 O S N Br HS S N 2

12 Page 2 2. Describe the following in a brief sentence and provide a pair of examples: [4 marks] a) conformers b) enantiomers 22. Draw the Newman Projections for,2-dichloroethane along the C-C axis using 60 o increments for all of the different conformations. a) Label each projection as being staggered, eclipsed. b) Identify an anti and a gauche conformer. c) Identify which one of these conformations represents the highest energy and which one of these conformations represents the lowest energy. [4 marks]

13 Page 3 OPTIONAL SECTION B (30 marks) ANSWER THREE (3) QUESTIONS ONLY FROM THIS SECTION EACH QUESTION IS WORTH 0 MARKS a. The reaction below has a K p of.23 x 0 3 at 800 C. Calculate the equilibrium partial pressures of the gases if 76 atm of CO is placed in a container at 800 C? [4 marks] C(s) + CO 2 (g) 2 CO(g)

14 Page 4 b. Consider a reaction where hydroxide reacts with (R)--cyclohexyl--iodoethane. The reaction rate depends on the concentration of both hydroxide and (R)--cyclohexyl--iodoethane. i) Provide the mechanism. Show the curly arrows, relevant lone pairs and all formal charges for each step, draw the intermediates and the product/s? ii) Is the stereochemistry of the product R, S or R and S? Give reasons. iii) Draw a energy diagram of the reaction of free energy versus reaction progress. iv) If HS was used as the nucleophile would the reaction be faster or slower. Give reasons. [6 marks]

15 Page 5 2a. The following data were collected for the reaction [5 marks] 2 A + 2 B P Initial Concentration (M) Initial Rate of Formation of P (M.s - ) Expt [A] [B] x x x ? i) What is the rate law for the reaction? ii) What is the value of the rate constant? (do not forget the units) iii) Use the data to calculate the reaction rate for the last experiment

16 Page 6 2b. Draw the structures of the product as shown by the curly arrows. [ mark] N C O 2c. The -phenylethyl cation is relatively stable. Explain why this is so. You must draw all the appropriate structures. [2 marks] 2d. For the following pairs of molecules, indicate which will act as a nucleophile (N) and which will act as an electrophile (E). Use the symbols E & N. [2 marks] Species CH 3 Br (CH 3 ) 3 N Nucleophile/Electrophile Species HI H 2 O Nucleophile/Electrophile

17 Page 7 3a. (S)--Iodo--phenylethane reacts with water. The product is a racemic mixture. Provide the mechanism. Show the curly arrows, relevant lone pairs and all formal charges for each step, draw the intermediates and the product/s. [3 marks] 3b. Describe the following in a brief sentence and provide an example: [2 marks] a) leaving group b) nucleophile

18 Page 8 3c. Find the ph of a buffer prepared by mixing 40.0 ml of 0.50 M acetic acid (CH 3 COOH) with 0.0 ml of M NaOH. K a (CH 3 COOH).76 x 0-5 M [5 marks]

19 Page 9 4a. If ml of M methylamine, (K b = 5.0 x 0-4 M at 25 C) is titrated with M HClO 4, what is the ph of the equivalence point? [6 marks]

20 Page 20 4b. For the reaction below, H = kj and S = J/K at 25 C. [4 marks] a) Calculate G for the reaction at 25 C and when = x 0-5 atm and = 0.0 atm. P SO2 b) Is this reaction spontaneous under these conditions? Show all necessary reasoning to support your answer. SO 2 (g) + H 2 O(l) + ½ O 2 (g) H 2 SO 4 (l) P O2

21 Page 2 5a. Under standard conditions at 25ºC, combustion of liquid cyclohexane is exothermic by kj/mol. Under the same conditions, combustion of gas-phase cyclohexane is exothermic by kj/mol. C 6 H 2 (l or g) + 9 O 2 (g) 6 CO 2 (g) + 6 H 2 O(l) a) Does the process C 6 H 2 (l) C 6 H 2 (g) have a positive or negative Sº value? Briefly explain your reasoning. b) What is the standard enthalpy of vapourization of cyclohexane at 25ºC? c) At 25ºC, the equilibrium constant for the process C 6 H 2 (l) C 6 H 2 (g) is The process is not spontaneous at this temperature under standard conditions. At what temperature does it become spontaneous? [7 marks]

22 Page 22 5b. Describe the following in a brief sentence: [3 marks] a) catalyst b) intermediate c) transition state

23 Page 23 Chem 2 Final April 5, 2004 DATA SHEET Conversions 0 C = 273 K Constants Gas constant, R = 8.34 J.mol -.K - = atm.l.mol -.K - 2a 4ac b b - = x T H S RT ln K G S T H G RT ln Q G G = K Q G = +RTln T H T nc H [acid] [salt] log pk ph T T R H K K ln (RT) K K T T R E k k ln Ae k k[a] t kt [A] [A] k ln 2 t kt ln[a] ln[a] kt [A] [A] 2 sys surr o o c p rxn a 2 O 2 n c p 2 a 2 RT E o 2 o 2 o o a ± = = = + + = + = = = = = = = = = = PERIODIC TABLE OF THE ELEMENTS H.00 2 He Li Be B C N O F Ne 20. Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Rb Sr Y Zr Nb Mo Tc (98) 44 Ru Rh Pd Ag Cd In Sn 8. 5 Sb Te I Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po 85 At 86 Rn 87 Fr 88 Ra Ac