Chemistry 225 Final Examination Time allowed: 3 hours Page 1 of 15. Student Name..Student Number Section.. g) K w = 1.

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1 hemistry 225 Final xamination Time allowed: 3 hours Page 1 of 15 You may use the following information wherever necessary: a) R = 8.31 J mol -1 K -1 = atm dm 3 mol -1 K -1 = atm L mol -1 K -1 b) k = e -a/rt c) k 2 ln = a 2 1 k [ ] d) ln t = kt [ 1 ] 0 ( T T ) R TT 1 2 e) ln t 1/2 = = k k f) K p = K c (0.0821T) n(gas) g) K w = at 298 K h) K a (H 3 OOH) = i) b ± b 4ac x = 2a j) [ base] ph = pk a + log [ acid] k) = o log Q n Section : Multiple hoice Select the best answer for each question and shade the letter corresponding to the answer on the answer sheet provided. [35 marks Questions 1-3 The reaction 2NO 2 - (aq) + 4 H I - (aq) I NO (g) + 2 H 2 O (l) is first order in nitrite ion and iodide ion and second order in hydrogen ion. 1. The rate law for the reaction is Rate = k [NO - 2 ] 2 [H + ][I - ] 2 Rate = k [NO - 2 ] 2 [H + ][I - ] Rate = k [NO - 2 ][H + ] 2 [I - ] Rate = k [NO - 2 ][H + ][I - ] 2 Rate = k [NO - 2 ] 2 [H + ] 4 [I - ] 2 2. If the rate of the reaction is expressed in M s -1, the correct unit for the rate constant, k, is M -2 s -1 M 2 s -1 M s -1 M -2 s -2 M -3 s y what factor would the rate of the reaction change if the concentrations of all the reactants are doubled? 1/

2 hemistry 225 Final xamination Time allowed: 3 hours Page 2 of mmonia can be oxidized according to the equation: 4 NH 3 (g) + 5 O 2 (g) 4 NO (g) + 6 H 2 O (g) If in a particular reaction the [NO] is mol dm -3, then [O 2 ], in mol dm -3, is -5/ / / / Which statement best explains the observation that reaction rates increase when temperature is increased? t a higher temperature the energy of activation is reduced. t a higher temperature the energy of activation is increased. t a higher temperature the concentration of the reactants is higher. t a higher temperature a larger fraction of reactant molecules have sufficient energy to form the transition state. t a higher temperature there is no need to form the transition state. 6. Which statement about catalysts is NOT true? catalyst has no effect on the enthalpy change for the reaction which it catalyses. catalyst does not participate in the reaction which it catalyses. atalysts are specific in their action. catalyst changes the rate of the forward and reverse reactions for a reversible reaction by the same factor. catalyst does not affect equilibrium position for a reversible reaction. 7. The following mechanism has been proposed for a reaction: Step 1: H 2 O 2 (aq) + I - (aq) H 2 O (l) + IO - (aq) slow Step 2: IO - (aq) + H 2 O 2 (aq) H 2 O (l) + O 2 (g) + I - (aq) fast Which statement is NOT consistent with this proposed mechanism? The overall reaction is: 2 H 2 O 2 (aq) 2 H 2 O (l) + O 2 (g) IO - is a reactive intermediate. I - is a catalyst. The reaction is first order with respect to the catalyst. The reaction is second order with respect to H 2 O 2.

3 hemistry 225 Final xamination Time allowed: 3 hours Page 3 of mol of NO 2 and 0.20 mol of l 2 were introduced into a 1 dm 3 vessel at constant temperature. When the system reached equilibrium, 0.16 mol of NOl was present. The reaction is: 2 NO 2 (g) + l 2 (g) 2NOl (g). Which set of values shows the concentration of each gas at equilibrium? [NO 2 ]/moldm -3 [l 2 ]/moldm -3 [NOl]/moldm The equilibrium constant for the reaction P(aq) Q(aq) is 3.2 x Which of the following statements is TRU? The equilibrium concentration of P is less than that of Q. The equilibrium concentration of P is greater than that of Q. dding a suitable catalyst will increase the equilibrium concentration of Q. dding a catalyst will increase the value of the equilibrium constant. dding more P to an equilibrium mixture of P and Q will increase the value of the equilibrium constant. 10. For which equilibrium system, at constant temperature, will decreasing the volume not cause the equilibrium position to shift? 2 O (g) + O 2 (g) 2 O 2 (g) (s) + O 2 (g) O 2 (g) Ol 2 (g) O (g) + l 2 (g) 2 NH 3 (g) N 2 (g) + 3 H 2 (g) ao 3 (s) ao (s) + O 2 (g) 11. onsider the process: Fe 2 O 3 (s) +3 H 2 (g) 3H 2 O (g) + 2 Fe (s) H = kj Which statement is NOT true for this system? K p = K c at a stated temperature. ddition of some H 2 to an equilibrium mixture will cause equilibrium to shift to the right. Increasing the mass of Fe 2 O 3 will cause equilibrium to shift to the right. The value of K p can be increased by increasing the temperature. ecreasing the volume of the container does not upset equilibrium.

4 hemistry 225 Final xamination Time allowed: 3 hours Page 4 of For the reaction Pl 5 (g) Pl 3 (g) + l 2 (g), K p = 1.7 at 298K. Five systems were set up with the initial partial pressure of each gas as shown in the table. In which system would the forward reaction occur to establish equilibrium? p i Pl 5 /atm p i Pl 3 /atm p i l 2 /atm ccording to the ronsted-lowry definition, a base is a species which donates a hydrogen atom. donates a hydrogen ion. accepts a hydrogen atom. accepts a hydrogen ion. accepts a hydroxide ion. 14. Which does NOT constitute an acid/base conjugate pair? - H 2 O 3 / HO 3 - NH 3 / NH 2 NH + 4 / NH 3 H 3 O + / OH - - HNO 2 / NO Which is a weak acid? HI HlO 4 Hr HF Hl 16. Which set shows the substances in order of increasing acid strength? HlO, HlO 2, HlO 3, H 2 SO 4, H 2 SO 3, HSO 4 - Hl, Hr, HF HF, H 2 O, NH 3 HPO 4 2-, H 3 PO 4, H 2 PO 4 -,

5 hemistry 225 Final xamination Time allowed: 3 hours Page 5 of The acidity constant for an acid, H, is The pk b of its conjugate base is closest to ssuming all of the following solutions have the same molar concentration, which one would be expected to have the lowest ph? Fel 3 Fel 2 al 2 Kl al 2 Questions refer to the following titrations: The titration of 20.0 cm 3 of 0.1M Hl with 0.1 M NaOH The titration of 20.0 cm 3 of 0.1M Hl with 0.1 M NH 3 The titration of 20.0 cm 3 of 0.1M H 3 OOH with 0.1 M NaOH The titration of 20.0 cm 3 of 0.1M KOH with 0.1 M Hl The titration of 20.0 cm 3 of 0.1M HNO 3 with 0.1 M KOH For which titration 19. would there be a decreases in ph as the titrant is added? 20. would the ph be greater than 7 at the equivalence point? 21. would the ph be lower than 7 at the equivalence point? 22. would phenolphthalein (ph range ) be unsuitable as an indicator? 23. would bromocresol green (ph range ) be unsuitable as an indicator? In which compound does hydrogen carry an oxidation number of 1? NH 4 NO 3 LiH H 2 O 2 NaHSO 4 HF

6 hemistry 225 Final xamination Time allowed: 3 hours Page 6 of In which compound does oxygen carry an oxidation number of -1? NaHSO 4 NH 4 NO 3 H 2 O 2 Fe 2 O 3 FeO 26. In which compound does oxygen carry an oxidation number of +2? F 2 O NH 4 NO 3 KHSO 4 uo u 2 O 27. Which is NOT a redox reaction? Zn + H 2 SO 4 ZnSO 4 + H 2 u + 2H 2 SO 4 uso 4 + SO 2 + 2H 2 O 2Nr 3 +H 2 O N 2 + 4r - + 2HOr ZnO 3 ZnO + O 2 XeF 2 +2l - Xe + 2F - + l Which is a disproportionation reaction? SO 2 + H 2 O H 2 SO 3 H 4 + 2O 2 O H 2 O 3 NO 2 + H 2 O 2 HNO 3 + NO 2 KMnO SO H 2 O 2 MnSO 4 + K 2 SO H 2 SO 4 S 2 O I - 2 SO I Which quantities are conserved in a redox reaction? Mass only. harge only. Oxidation number. Neither mass nor charge. oth mass and charge.

7 hemistry 225 Final xamination Time allowed: 3 hours Page 7 of The e.m.f. of the cell: Pt (s) H 2 (g) Hl (aq) uso 4 (aq) u (s) does NOT depend on temperature. the size of the copper electrode. the concentration of Hl. the concentration of uso 4. the pressure of H When the contents of an electrochemical cell are at equilibrium, the e.m.f. of the cell is zero. is at a maximum. is negative. is positive. cannot be measured Questions concern the following graphs: Select, from to, the graph which best represents: 32. Rate of reaction versus concentration of X for a reaction which is zero order in X. 33. Rate of reaction versus concentration of X for a reaction which is first order in X. 34. Rate of reaction versus time for a reversible process which attains equilibrium after some time. 35. The titration curve for the titration of a base with an acid.

8 hemistry 225 Final xamination Time allowed: 3 hours Page 8 of 15 STION : nswer LL questions in the spaces provided on the question paper. Remember to include units in your answers wherever appropriate. 1. The following data were obtained for the reaction: 6 I - (aq) + ro 3 - (aq) + 6 H + (aq) 3 I 2 (aq) + r - (aq) + 3 H 2 O (l) xperiment Initial [I - ]/M Initial [ro - 3 ]/M Initial [H + ]/M Initial Rate of I 2 formation/ms a) erive the rate law for the reaction. [3 ] b) i) Use the data from experiment 1 to find the value of the rate constant, k, stating its correct units. [2] ii) What would be the value of the rate constant if the concentration of all reactants were doubled? [1] c) What effect, if any, would doubling the concentration of the reactants have on the energy of activation for the process? [1]

9 hemistry 225 Final xamination Time allowed: 3 hours Page 9 of 15 d) What effect, if any, would increasing the temperature of the reaction mixture have on the energy of activation for the process? [1] e) What effect, if any, would increasing the temperature of the reaction mixture have on the value of the rate constant for the process? [1] f) What effect, if any, would using a catalyst have on the energy of activation for the process? [1] 2. The activation energy for the reaction: 2 N 2 O (g) 2 N 2 (g) + O 2 (g) is 200 kj mol -1. How many times faster would this reaction proceed at 230 o than at 200 o? [4] 3. The first order rate constant for the decomposition of a certain hormone in water at 25 o is day -1. a) If a M solution of the hormone is stored for 40 days, what will be its concentration at the end of that period? [3]

10 hemistry 225 Final xamination Time allowed: 3 hours Page 10 of 15 b) What is the half life of the hormone? [2] c) How many days will it take for a sample of the hormone to be 65% decomposed? [2] 4. Use the given K p values for the processes X and Y to find K p for the process Z. [2 ] Process X: 2 rf (g) r 2 (g) + F 2 (g) K p = K x = Process Y: r 2 (g) + 3 F 2 (g) 2 rf 3 (g) K p = K y = 5.29 Process Z: rf 3 (g) rf (g) + F 2 (g) K p = K z

11 hemistry 225 Final xamination Time allowed: 3 hours Page 11 of The equilibrium constant, K p, for the dissociation of dinitrogen tetroxide to nitrogen dioxide is 11 at 398K. The reaction is: N 2 O 4 (g) 2 NO 2 (g). a) Find the equilibrium partial pressure of each gas when N 2 O 4, at an initial pressure of 1.20 atm, dissociates at 398 K. [6] b) Find the total pressure of the system at equilibrium. [1 ] c) Find the percent dissociation of dinitrogen tetroxide. [1] 6. Find the ph of a) M NaOH [1]

12 hemistry 225 Final xamination Time allowed: 3 hours Page 12 of 15 b) M H 3 OOH [5] c) a mixture of 20.0 cm 3 of M H 3 OOH cm 3 of M NaOH [7]

13 hemistry 225 Final xamination Time allowed: 3 hours Page 13 of 15 d) a mixture of 30.0 cm 3 of M H 3 OOH cm 3 of M NaOH [5] e) a mixture of 20.0 cm 3 of M H 3 OOH cm 3 of M NaOH [4] 7. erive a balanced ionic equation for the reaction by writing half equations and then combining them. PbS (s) + NO 3 - (aq) S (s) + Pb 2+ (aq) + NO (g) (in acid medium) [4 ]

14 hemistry 225 Final xamination Time allowed: 3 hours Page 14 of Use the following table of standard redox potentials wherever necessary. o /V MnO - 4 (aq) + 8 H + (aq) + 5 e - Mn 2+ (aq) + 4 H 2 O (l) l 2 (g) + 2e - 2l - (aq) g + (aq) + e - g (s) Fe 3+ (aq) + e - Fe 2+ (aq) NiO 2 (s) + 2 H 2 O (l) + 2e - Ni(OH) 2 (s) + 2 OH - (aq) u 2+ (aq) + 2e - u (s) H + (aq) + 2e - H 2 (g) 0.00 Ni 2+ (aq) + 2e - Ni (s) Fe 3+ (aq) + 3e - Fe (s) d 2+ (aq) + 2e - d (s) Fe 2+ (aq) + 2e - Fe (s) d(oh) 2 (s) + 2e - d (s) + 2 OH - (aq) Mg 2+ (aq) + 2e - Mg (s) a) Rechargeable nickel-cadmium cells are used in calculators and other battery powered devices. The cell reaction is: NiO 2 (s) + d (s) + 2 H 2 O (l) Ni(OH) 2 (s) + d(oh) 2 (s). What is the cell potential of a standard nickel-cadmium cell? [1] b) The cell notation represents a standard galvanic cell: Mg (s) Mgl 2 (aq) Fel 3 (aq), Fel 2 (aq) Pt (s) i) Write a balanced ionic equation for the cell reaction. [1 ] ii) raw a fully labeled diagram of the galvanic cell. Show the direction of flow of electrons, the polarity of the electrodes and the concentration of all solutions. [5]

15 hemistry 225 Final xamination Time allowed: 3 hours Page 15 of 15 c) i) Find the standard cell potential for a cell in which the reaction: g + (aq) + Fe 2+ (aq) g(s) + Fe 3+ (aq) takes place. [1] ii) Find K c for the process: g + (aq) + Fe 2+ (aq) g(s) + Fe 3+ (aq) [4] d) Find the e.m.f of the cell: u (s) u 2+ (0.001 M) u 2+ (0.250 M) u (s) [4] e) xplain why hydrochloric acid cannot be used to provide an acid medium with potassium manganate (VII) as an oxidizing agent. [2] N OF XMINTION

PHYSICAL SCIENCES: PAPER II

PHYSICAL SCIENCES: PAPER II NTIONL SENIOR ERTIFITE EXMINTION SUPPLEMENTRY EXMINTION 2015 PHYSIL SIENES: PPER II Time: 3 hours 200 marks PLESE RE THE FOLLOWING INSTRUTIONS REFULLY 1. This question paper consists of 13 pages, an nswer