BCIT Winter 2017 Chem 0012 Final Exam Name: Attempt all questions in this exam. Read each question carefully and give a complete answer in the space provided. Part marks given for wrong answers with partially correct reasoning/calculations. Constants, equations, data sheets and tables are provided. Good luck in the future! Total points = 50 Page 1 of 12
Section I: Multiple choice (25 points total, 1 point each) Choose the BEST answer to the following questions. 1. Given the reaction: CaCO 3 (s) + 2HCl(aq) CaCl 2 (aq) + H 2 O() + CO 2 (g) + heat Which of the following will cause the reaction rate to increase? a. increasing the pressure b. decreasing the pressure c. increasing the temperature d. decreasing the temperature 2. Consider the following reaction: Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) In two different experiments, equal moles of Zn and equal volumes of HCl are reacted. After 2 minutes, the volume of H 2 produced is recorded as follows: Zn [HCl] Temperature Volume H 2 Experiment 1 strip 10.0 M 10 C 10.6 ml Experiment 2 Powdered 3.0 M 15 C 7.3 ml Which of the following factors explains why the rate in Experiment 1 is different than the rate in Experiment 2? a. nature of reactants b. surface area of Zn c. [HCl] d. temperature 3. Which statement is true? a. The pre exponential factor, A, in the Arrhenius equation is related to the correct spatial orientation of the reactants. b. The rate of a reaction always increases doubles when the temperature is increased 10 C. c. When a catalyst is added, the rate of the reaction is increased because the activation energy of the reaction is increased. d. The rate constant of a reaction is independent of temperature. Page 2 of 12
4. Consider the following reaction: Which of the following could be true of the activated complex? Structure Potential Energy (relative to reactants) a. lower b. higher c. lower d. higher 5. What is the effect of adding a catalyst to an equilibrium system? a. The value of E a increases. b. The value of K eq increases. c. Forward and reverse reaction rates increase. d. The concentration of products increases. 6. Which of the following reactions has decreasing enthalpy and increasing entropy? a. Hg() + ½O 2 (g) HgO(s) ΔH = 91 kj b. 2HCl(g) H 2 (g) + Cl 2 (g) ΔH = 185 kj c. 2HgO(s) 2Hg() + O 2 (g) ΔH = 182 kj d. 2SO 3 (g) SO 2 (g) + O 2 (g) ΔH = 200 kj Page 3 of 12
7. Consider the following potential energy diagram: Which of the following could be true for the forward reaction? ΔH (kj) E a (kj) a. 150 300 b. 150 600 c. 150 300 d. 150 600 8. What is K eq expression for the following equilibrium? 2KClO 3 (s) 2KCl(s) + 3O 2 (g) a. b. c. d. 9. If a reaction is in a state where Q < K, a. the concentration of reactants and products will both decrease b. the concentration of reactants and products will both increase c. the concentration of reactants will decrease and the concentration of products will increase d. the concentration of reactants will increase and the concentration of products will decrease Page 4 of 12
10. Consider the following equilibrium system: 2NO(g) + Cl 2 (g) 2NOCl(g) ΔH = 77kJ In which direction will the equilibrium shift and what happens to the value of K eq when NO(g) is added to the system? Shift K eq a. right increases b. right stays constant c. left stays constant d. left decreases 11. What is the K sp expression for Zn(OH) 2? a. K sp = [Zn 2+ ] [OH ] 2 b. K sp = [Zn 2+ ] 2 [OH ] c. K sp = [Zn 2+ ] (2[OH ]) 2 d. K sp = [Zn 2+ ] + 2 [OH ] 2 12. An acid is added to water and a new equilibrium is established. The new equilibrium can be described by a. ph < poh and K w = 1x10 14 b. ph < poh and K w < 1x10 14 c. ph > poh and K w =1x10 14 d. ph > poh and K w > 1x10 14 13. When the [H 3 O + ] in a solution is increased to twice the original concentration, the change in ph could be from a. 1.7 to 1.4 b. 2.0 to 4.0 c. 5.0 to 2.5 d. 8.5 to 6.5 14. What is the K a value for the indicator that is yellow in its basic form and blue in its acid form? a. 6x10 13 b. 2x10 9 c. 2x10 7 d. 3x10 5 Page 5 of 12
15. Which of the following salt solutions is acidic? a. KBr b. NaNO 2 c. NaHC 2 O 4 d. NH 4 CN 16. Which of the following situations will results in a solution with the highest ph? a. A low concentration of a base with a low value of K b b. A low concentration of a base with a high value of K b c. A high concentration of a base with a low value of K b d. A high concentration of a base with a high value of K b 17. Identify the two conjugate pairs in the equilibrium provided? H 2 PO 4 + HCO 3 HPO 2 4 + H 2 CO 3 Pair 1 Pair 2 a. H 2 PO 4 /H 2 CO 3 HCO 3 /HPO 4 ² b. H 2 PO 4 /HPO 4 ² HCO 3 /H 2 CO 3 c. H 2 PO 4 /HCO 3 HPO 4 ² /H 2 CO 3 d. H 2 PO 4 /OH HCO 3 /H + 18. When NO 2 acts as a reducing agent, a possible product is a. NO b. N 2 O c. N 2 O 4 d. N 2 O 5 19. In an operating electrochemical cell the function of a salt bridge is to a. allow hydrolysis to occur b. allow a non spontaneous reaction to occur c. permit the migration of ions with the cell d. transfer electron from the cathode to the anode Page 6 of 12
Use the following diagram to answer questions 20 22 20. As the cell operates, electrons flow toward a. the Pb electrode, where Pb is oxidized. b. the Cd electrode, where Cd is oxidized. c. the Pb electrode, where Pb 2+ is reduced. d. the Cd electrode, where Cd 2+ is reduced. 21. As the cell operates, the cations move towards the a. the Pb electrode and the Pb electrode gains mass. b. the Pb electrode and the Pb electrode loses mass. c. the Cd electrode and the Cd electrode gains mass d. the Cd electrode and the Cd electrode loses mass 22. The E value of the reduction of Cd 2+ is a. 0.40 V. b. 0.27 V c. +0.14 V d. +0.40 V Page 7 of 12
23. The oxidations number of manganese changes as MnO 4 is converted to MnO 2. How many electrons are gained or lost by the manganese during the change? a. 1 e lost b. 1 e gained c. 3 e lost d. 3 e gained 24. What is the reducing agent in the following reaction? a. Fe 3+ b. I c. Fe 2+ d. I 2 2Fe 3+ + 2I 2Fe 2+ + I 2 25. Which metal, Al or Sn could reduce Zn 2+ to Zn(s) if placed in a 1 M Zn 2+ (aq) solution at 25 C? a. Al b. Sn c. Both Al and Sn would work. d. Neither Al or Sn would work. Section II: Written problems (25 points total). 26. Consider the following reaction in an open flask: Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) A 0.024 g sample of Mg reacts completely with HCl in 14.0 s. Calculate the average rate of consumption of HCl in mol/s? (2 points) 0.024 2 14.0 24.3 1.410 / Page 8 of 12
27. A reaction has the following mechanism. 2NO + H 2 N 2 + H 2 O 2 H 2 O 2 + H 2 2H 2 O a. What is the overall reaction? (1 point) slow fast 2NO + 2H 2 N 2 + 2H 2 O b. What is the reaction s rate law? (2 points) the first step is the rate determining step rate = k[no]²[h 2 ] c. The intermediate in the reaction is: H₂O₂ (1 point) d. Circle the correct answer for how adding NO or H 2 O will affect the overall reaction rate. (2 points) NO decrease no change increase H 2 O decrease no change increase 28. A sample of pure NaOH is dissolved in water to make 10.0 L of solution which has a phof= 10.75. Calculate the mass of pure NaOH that was dissolved. (2 points) poh = 14.00 ph = 14.00 10.75 = 3.25 10 10. 10. 10.0 40.0 0.22 Page 9 of 12
29. Consider the following equilibrium: N 2 (g) + O 2 (g) 2NO(g) K eq = 9.5x10 3 Initially, 1.5 mol N 2 and 1.5 mol of O 2 were placed in a 10.0 L container. Calculate the concentration of all species at equilibrium. (4 points) [N 2 ] o = [N 2 ] o = (1.5 mol)/(10.0 L) = 0.15 M N 2 + O 2 2NO I 0.15 0.15 0 C x x 2x E 0.15 x 0.15 x 2x. 9.710 2 9.510 0.15 Note square root must be positive since it is the ratio of two concentrations 0.159.710 2 9.710 7.010 [N 2 ] = [O 2 ] = 0.15 M 0.0070M = 0.14 M [NO] = 2(0.0070 M) = 0.014 M 30. An acid base reaction occurs between HSO 3ˉ and IO 3ˉ. a. Write the equation for the predominant equilibrium that results (1 point) HSO 3ˉ + IO 3ˉ SO 3 ²ˉ + HIO 3 b. Are the reactants or products favoured? Explain your reasoning. (2 points) Reactants are favoured K a (HIO 3 ) > K a (HSO 3ˉ) Page 10 of 12
31. A mixture is prepared by adding 20.0 ml of 0.400 M CuSO 4 and 30.0 ml of 0.300 M KIO 3. What mass in grams of Cu(IO 3 ) 2 will be formed and what will be the concentration of each of the ions after the reaction? The molar mass of Cu(IO 3 ) 2 is 413.35 g/mol. (5 points) Cu 2+ (aq) + 2IO 3 (aq) Cu(IO 3 ) 2 (s) K sp = 6.9x10 8 = [Cu 2+ ][IO 3 ] 2 20.0 0.400 20.0 30.0 0.160 30.0 0.300 20.0 30.0 0.180 Cu(IO 3 ) 2 (s) Cu 2+ (aq) + 2IO 3 (aq) I 0.160 0.180 R 0.090 0.180 C x 2x E 0.070 + x 2x 6.910 0.070 2 0.0704.. 5.010 assumption that x << 0.07 is OK 0.070 5.010 0.070 25.010 1.010 0.160, 0.180 0.090 0.050 413.35 1.86 32. Balance the following redox reaction in acidic solution: (3 points) Br + BrO 3 Br 2 5(2Br Br 2 + 2e ) 10e + 12H + + 2BrO 3 Br 2 + 6H 2 O 10Br + 2BrO 3 + 12H + 6Br 2 + 6H 2 O or 5Br + BrO 3 + 6H + 3Br 2 + 3H 2 O Page 11 of 12
Chem 0012 Equations and Constants PV = nrt T(K) = T( C) + 273.15 R = 0.0820575 L atm mol 1 K 1 = 8.314 J mol 1 K 1 ln 1 ln y = mx + b PV = nrt K p = K c (RT) Δn 1 atm = 760 mm Hg = 760 Torr = 101.325 kpa ph = log[h + ] poh = log[ohˉ] [H + ] = 10 ph [OHˉ] = 10 poh px = log(x) X = 10 px K w = 1.0x10 14 @ 25 C 14.00 = ph + poh @ 25 C K w = K a K b [ A ] ph pka log [ HA ] F = 96485 C/mol ln. log at 25 C The solution to the quadratic equation ax² + bx +c = 0 is b b 2 4ac x 2a Page 12 of 12