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2 Chem 126 Common 3 Part I April, 24, What is the oxidation state of manganese in MnO 4? (a) 1 (b) 2 (c) 3 (d) 5 (e) 7 2. Which of the following compounds has the largest entropy? Careful (a) H 2 (g) (b) H 2 O (g) (c) H 2 O (l) (d) H 2 O (s) (e) SiO 2 (s) 3. What is the change in E, when 2.0 x 10 3 J of heat is lost and the system expands from 1.0 to 11.0 L against an external pressure of 1.4 atm. (1 L atm = J) (a) -3,400 J (b) -600 J (c) 3,400 J (d) 600 J (e) -2,000 J 4. For which of the following processes is the change spontaneous? (a) The change in entropy of the universe decreases. (b) At constant pressure, H sys > 0 (endothermic), S sys > 0 and T is very small. (c) At constant pressure, H sys > 0 (endothermic), S sys > 0 and T is very large. (d) Ln(Q/K eq ) > 0 (e) The voltage for the reaction < 0. H S o f o f -1 1 ( K ) CH OH l CH OH ( g ) 3 3 kj/mol Jmol Calculate the boiling point of methanol (CH 3 OH). (a) K (b) 1198 K (c) 348 K (d) 342 K (e) 336 K 6. Calculate the approximate vapor pressure of methanol at 300 K. (a) atm (b) 0.19 atm (c) 0.50 atm (d) 0.29 atm (e) > 1 atm

3 7. Calculate the change in entropy for the following reaction: N 2 H 4 (l) + 2O 2 (g) 2NO 2 (g) + 2H 2 O (l) S J/ mol/ K : (a) 86 Jmol -1 K -1 (b) -16 Jmol -1 K -1 (c) 16 Jmol -1 K -1 (d) -89 Jmol -1 K -1 (e) 89 Jmol -1 K -1 o f J is added to 2.0 grams of iron. What is the change in its temperature? Hint, use the law of Dulong et Petit to find the specific heat of iron, that is, the molar heat capacity of all metals is about 25 J/(mol o C). Aside, it comes from the fact that metals all take up heat the same way, namely, the atomics vibrate more strongly. (a) 8 o C (b) 50 o C (c) 100 o C (d) 110 o C (e) >150 o C 9. In a Galvanic cell, which of the following statements is NOT true about a STANDARD half-cell with a zinc electrode and a zinc sulfate solution: (a) The size of the zinc electrode does not matter. (b) The concentration of ZnSO 4 is 1 M. (c) This half-cell is always the anode because zinc is an active metal. (d) This half-cell can be either an anode or a cathode. (e) There are 2 moles of electrons in the balance half-reaction for this half-cell. 10. What is the voltage of the following reaction for standard conditions: Cr ( aq) + Cu 2Cr ( aq) + Cu ( aq) (a) V (b) 0.84 V (c) V (d) 1.34 V (e) V Cr aq + e Cr 0.50V 2+ Cu aq + 2e Cu V 11. What is the voltage of the following reaction for the specified conditions: (a) 1.27 V 2Al(s) + 6H + (aq) 2Al 3+ (aq) + 3H 2 (g) Eº =1.66 V (b) 0.48 V 54g M 0.80 M 5.0 atm (c) 1.62 V (d) 1.46 V (e) 1.47 V

4 12. Calculate the value of the solubility product constant for PbSO 4 from the half-cell potentials. (a) 1.9x10-4 PbSO 4 (s) + 2e - Pb(s) + SO 2-4 (aq) E o = V (b) 3.6x10-8 Pb 2+ (aq) + 2e - Pb(s) E o = V (c) 7.6x10-9 (d) 5.7x10-17 (e) 1.2x What mass of Fe(III) ions is plated from an average current of 50.0 A for 3.0 hours? (a) 1.0x10 2 g (b) 69 g (c) 35 g (d) 1.7g (e) 65 g 14. An underground iron pipe in damp soil is to be protected from rusting. Which of the following techniques would NOT work? Useful info: Fe 2+ (aq) + 2e - Fe(s) E o = V (a) The iron pipe is electrically connected using a wire to a Mg rod. (Mg 2+ (aq) + 2e - Mg(s) E o = V) (b) The iron pipe is electrically connected to bar of Zn. (Zinc is a more active metal than iron.) (c) The iron pipe is connected to the positive end of a battery and the negative end is connected to an iron bar. (d) The iron pipe is painted with several coats of paint. (e) The iron pipe is galvanized. 15. The concentration of a solution sodium iodide ion will be determined by titrating 90 ml of it using potassium permanganate. After 60.0 ml of M KMnO 4 is added the purple color of potassium permanganate persists indicating the end of the titration. What is the concentration of NaI? (a) M (b) M (c) M (d) M (e) M 16. In a living organism, the decay of C-14 produces 15.3 disintegrations per minute per gram of carbon. The half-life of C-14 is 5730 years. A 0.80 g sample of bone has 10.3 disintegrations per minute. How old is the bone sample in years? (a) 3270 (b) 1,430 (c) 612 (d) <500 (e) >5, MnO aq I aq H O l IO aq 2MnO s 2OH aq

5 Part II (36 points) I. The following reaction will be balanced in a acidic MnO aq H C O aq Mn aq + CO g solution: (a) (3 pts) What is one of the balanced half-reactions? Circle: oxidation or reduction half-reaction (b) (3 pts) What is the other balanced half-reaction? Circle: oxidation or reduction half-reaction (c) (3 pts) What is the balanced reaction? (d) (3 pts) If the reaction were balanced in a basic solution, what would be the overall balanced reaction?

6 II. (a) (4 pts) What is the free energy of reaction for: CH ( g) + 5O ( g) 3CO ( g) + 4HO( g) Gº rxn (kj/mol) (b) (4 pts) What is the approximate standard change in enthalpy for the reaction, Hº rxn? (Use the bond energies given in the table.) (c) (4 pts) What is the approximate value of the standard entropy change for the reaction, Sº rxn?

III. (a) (4 pts) What is A X for the following fictitious reaction: A + 0 β 215 At+ 4 α Z Z X 1 85 2 (b) (4 pts) C-12 is a stable isotope of carbon.

7 III. (a) (4 pts) What is A X for the following fictitious reaction: A + 0 β 215 At+ 4 α Z Z X (b) (4 pts) C-12 is a stable isotope of carbon. C-14 is not stable because it has too many. The expected decay mode for C-14 is. (c) (4 pts) What is the mass defect for Al-27 in amu? Its atomic mass is

Name AP CHEM / / Collected Essays Chapter 17

Name AP CHEM / / Collected Essays Chapter 17 1980 - #2 M(s) + Cu 2+ (aq) M 2+ (aq) + Cu(s) For the reaction above, E = 0.740 volt at 25 C. (a) Determine the standard electrode potential for the reaction