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Unformatted text preview: Chemistry 1800 U General Chemistry for Engineers W09 FINAL EXAM 2009.04.14 Name:_____________________________Student Number:__________________ INSTRUCTIONS 1) With the exception of the SCANTRON card, the examination must be completed in pen. No white-out or similar product may be used. Examinations submitted in pencil will not be eligible for appeal. 2) Mark your answers to the multiple choice questions on the Scantron card using PENCIL. Choose only one answer for each question. The answers on the examination will only be marked if no Scantron card is available. 3) The formula and data sheets may be removed if you wish. These are the only data sheets that are permitted. 4) You may use a non-programmable, scientific calculator. No other electronic aids are permitted. 5) Part II consists of “worked” problems. These must be answered in the space provided. You may use the back of the pages for rough work or for extra space as necessary. 6) At the end of the exam submit the entire examination (with the exception of the formula and data sheets). Marker’s Use: Section 1: /28 Section 2: /44 1 Multiple Choice Short Answers Total /72 Section 1: Multiple Choice (28 marks) 1) A piece of metal ore weighs 8.25 g. When a student places it into a graduated cylinder containing water, the liquid level rises from 21.25mL to 26.47mL. What is the density of ore? a. 0.312 g/mL b. 0.633 g/mL c. 1.58 g/mL d. 3.21 g/mL 2) What is the identity of element Q if the Q2+ ion contains 10 electrons? a. C b. O c. Ne d. Mg 3) What is the sum of the coefficients when the following equation is balanced using the lowest, whole number coefficients? ________ PH3(g) + ________ O2(g) ________ P4O10(s) + ________ H2O(g) a. b. c. d. 10 12 19 22 4) Which of the following is not a valid set of quantum numbers? a. n = 2, l = 1, ml = 0, ms = ‐ ½ b. n = 2, l = 1, ml = ‐1, ms = ‐ ½ c. n = 3, l = 0, ml = 0, ms = +½ d. n = 3, l = 2, ml = 3, ms = + ½ 5) Which element has a 3+ ion with the electron configuration [Kr]4d5 a. Sc b. Ru c. Pd d. Ag 2 6) Which element has the most favourable (most negative) electron affinity? a. Na b. Mg c. O d. Ne 7) What is the molecular geometry of BrF4‐ according to the VSEPR Model? a. Seesaw b. Square planar c. Square pyramidal d. Tetrahedral 8) Which has a dipole moment? a. CO2 b. H2O c. SO2 d. CH4 9) Which transition could occur if a solid is heated at a pressure above the triple point pressure? a. Condensation b. Deposition c. Melting d. Sublimation 10) Calculate the freezing point of a solution prepared by dissolving 20.0g of methyl salicylate, a nonelectrolyte of molar mass = 152.15 g/mol, in 800 g of benzene, C6H6. The freezing point of benzene is 5.50 oC and Kf(benzene) = 5.10 oC/m. a. b. c. d. ‐1.05oC 1.05oC 4.45oC 4.66oC 3 11) It takes 11.2 kJ of energy to raise the temperature of 145 g of benzene (C6H6) from 25.0 °C to 70.0 °C. What is the specific heat of benzene? a. 3.48 J/(g ∙ °C) b. 1.72 J/(g ∙ °C) c. 1.10 J/(g ∙ °C) d. 5.41 J/(g ∙ °C) 12) Given: 4 NO2(g) + O2(g) → 2 N2O5(g) ΔH° = ‐110.2 kJ. Find ΔH° for: N2O5(g) → 2 NO2(g) + 1/2 O2(g). a. ‐55.1 kJ b. 220.4 kJ c. ‐220.4 kJ d. 55.1 kJ 13) Hydroquinone, HOC4H4OH, can be formed by the reaction with acetylene below: 3 HCCH + 3 CO + 3 H2O → 2 HOC4H4OH + CO2 How is the rate of disappearance of acetylene, HCCH, related to the appearance of hydroquinone (Hq)? ‐ (Δ[HCCH]/ΔT) = ? a. + (Δ[Hq]/Δt) b. + (Δ[Hq]/Δt) c. + (Δ[Hq]/Δt) d. + (Δ[Hq]/Δt) 14) A plot of 1/[BrO‐] vs time is linear for the reaction: 3 BrO‐(aq) → BrO3‐(aq) + 2 Br‐(aq) What is the order of the reaction with respect to the hypobromite ion, BrO‐? a. 0 b. 1 c. 2 d. 3 4 15) For which of the following reactions or changes does entropy INCREASE? 2NH3(g) a. N2(g) + 3H2(g) b. Cooling nitrogen gas from 20 ºC to –20 ºC. NH4Cl(s) c. HCl(g) + NH3(g) d. CaCO3(s) CaO(s) + CO2(g) 16) For the reaction shown below, which change in conditions made to the system at equilibrium will result in a net reaction to the right to form more product? C(s) + 2 H2(g) CH4(g) H° = – 74.8 kJ a. increasing the concentration of CH4 b. decreasing the concentration of H2 c. increasing the concentration of H2 d. adding more C 17) Which one of the following salts produces a solution with the highest pH, if the same amount of salt is dissolved in 1 L of water? a. KCl b. KBr c. KF d. KI 18) In the following chemical equation indicate the reactant that is a Br nsted‐Lowry acid HCN(aq) + H2O(l) H3O+(aq) + CN‐(aq). a. b. c. d. CN‐ HCN H2O H3O+ 19) Which is the best acid to use in the preparation of a buffer with pH = 3.3? a. HNO3 b. HIO3 (Ka = 1.7 × 10–1) c. HNO2 (Ka = 4.5 × 10–4) d. HOI (Ka = 2.0 × 10–11) 5 20) What is the reduction half‐reaction for the following overall galvanic cell reaction? Co2+(aq) + 2 Ag(s) → Co(s) + 2 Ag+(aq) a. Co2+(aq) + 2 e‐ → Co(s) b. Co2+(aq) + e‐ → Co(s) c. Ag+(aq) + e‐ → Ag(s) d. Ag(s) + e‐ → Ag+(aq) 21) Doubling all the coefficients in the equation for the cell reaction Ni2+(aq) + Cd(s) → Cd2+(aq) + Ni(s) a. doubles ΔG°, but does not change E°. b. doubles E°, but does not change ΔG°. c. does not change E° or ΔG°. d. doubles both E° and ΔG°. 22) What is the relation between ΔG° and E° for the cell reaction below? Ni2+(aq) + Cd(s) → Cd2+(aq) + Ni(s) a. ΔG° = ‐F E° b. ΔG° = 2 F E° c. ΔG° = F E° d. ΔG° = ‐2 F E° 23) Silver chloride has a solubility of 0.007 mg/mL in water at 5 oC. What is the osmotic pressure of a saturated solution of AgCl? (Molar mass of AgCl = 143.22 g/mol) a. b. c. d. 2.2 x 10‐3 atm 1.1x10‐3 atm 2.0 x 10‐5 atm 4.9 x 10‐5 atm 24) What are the conjugate acid‐base pairs in the following chemical reaction NH3(aq) + H2O(l) NH4+(aq) + OH‐(aq)? a. NH3 and NH4+ b. NH3, NH4+ and H2O, OH‐ c. NH3, OH‐ and H2O, NH4+ d.NH3, H2O and NH4+, OH‐ 6 25) What is the pH of a 0.025 M HCl solution? a. 1.00 b. 2.00 c. 3.20 d. 1.60 26 ) A salt bridge is used to a. control whether the cell is electrolytic or galvanic. b. determine the direction of the cell reaction. c. provide reactants in a fuel cell. d. allow the ion flow necessary for cell neutrality. 27) During an electrochemical reaction, electrons move through the external circuit toward the ________ and positive ions in the cell move toward the ________. a. cathode, cathode b. anode, cathode c. cathode, anode d. anode, anode 28) Which cell involves a nonspontaneous redox reaction? a. concentration cell b. electrolytic cell c. galvanic cell d. fuel cell 7 Section 2: Worked Problems (44 marks) __________________________________________________________________ 29) (4 marks) Lithium hydroxide, LiOH, is used in spacecrafts to recondition the air by absorbing the carbon dioxide exhaled by astronauts. The reaction is: 2LiOH(s) + CO2(g) Li2CO3(s) + H2O(l) What volume of CO2 gas at 21oC at 781 mmHg could be absorbed by 327 g of Lithium hydroxide? 30) (3 marks) What is the molarity of each ion in a solution prepared by dissolving 0.550g of Na2SO4 (molar mass = 142.04 g/mol) and diluting to a total volume of 100mL? 8 31) (2 marks) How many millilitres of a 9.0 M H2SO4 solution are needed to make 0.25 L of a 3.5 M H2SO4 solution? 32) (3 marks) What is the pH of a 0.002 M Ba(OH)2 solution? 9 33) (3 marks) Ammonium nitrate is dangerous because it decomposes (sometimes explosively) when heated. NH4NO3(s)→N2O(g) + 2H2O (g) Show the decomposition of solid ammonium nitrate is spontaneous at 25 oC and 1 atm. Gibbs energies of formation of N2O, H2O, and NH4NO3 : ΔGof (N2O) = 104.2 kJ/mol / ΔGof (H2O) = ‐228.6 kJ/mol / ΔGof (NH4NO3) = ‐184.0 kJ/mol 34) (6 marks total) Chlorine gas, Cl2(g), reacts with nitric oxide, NO (g), to form nitrosyl chloride, NOCl(g), via the reaction: Cl2(g) + 2 NO (g) ↔ 2 NOCl (g) ΔGorxn = ‐40.82 kJ/mol at 25 oC (a) Calculate the equilibrium constant, Kp, for the formation of nitrosyl chloride at 25 oC. (3 marks) (b) Calculate the free energy, ΔG, at 25 oC if the partial pressures of chlorine, nitric oxide, and nitrosyl chloride are 1 atm, 2 atm, and 3.58x109 atm, respectively. (2 marks) (c) Is the reaction at equilibrium under the conditions given in part b? (1 mark) 1 0 35) (6 marks total) The initial rates listed in the table were determined for the thermal decomposition of azomethane (CH3N=NCH3): CH3N=NCH3 (g) → C2H6 (g) + N2 (g) Initial [CH3N=NCH3] M 2.4 x 10‐2 8.0 x 10‐3 Initial rate of decomposition of [CH3N=NCH3] (M/s) 6.0 x 10‐6 2.0 x 10‐6 Experiment 1 2 (a) What is the rate law? (2 mark) (b) What is the value of the rate constant for the decomposition reaction? (1 marks) (c) Calculate the percentage of azomethane that it will decompose in 10 minutes if the initial concentration of azomethane is equal to 1.5×10−2M. (3 marks) 1 1 36) (10 marks total) For the following electrochemical cell: Zn(s)| Zn2+(1 M) || H+(?M) | H2(1 atm)|Pt (a) What reaction takes place at the anode? (1 mark) (b) What reaction takes place at the cathode? (1 mark) (c) What is the overall cell reaction? (1 marks) (d) What is the pH of the solution in the cathode compartment of the following cell if the measured cell potential at 25 oC is 0.55 V? (5 marks) (e) Calculate ΔG at 25oC. (2 marks) 1 2 37) (7 marks total) For the acid dissociation reaction: C6H5COOH (aq) + H2O(l) C6H5COO‐(aq) + H3O+(aq) pKa= 4.19 at 25 oC. (a) Calculate the hydronium ionconcentration of a solution prepared by dissolving 0.15 mol of benzoic acid (C6H5COOH) and diluting to a total volume of 500 mL? (4 marks) (b) What is the pH of this solution? (1 mark) (c) Calculate the pH of a buffer solution prepared by adding 0.15 mol of C6H5COONa to the solution described in part (a). (2 marks) 1 3 CHEM 1800­FORMULA AND DATA SHEET R = 8.314 J mol‐1 K‐1 = 0.0821 L atm mol‐1 K‐1 F = 9.65 x 104 C mol‐1 1 atm = 101.325 kPa = 1.01325 bar 0oC = 273 K 1 cal = 4.184 J 1 L = 1 dm3 Avogadro’s Number, N = 6.022 x 1023 [ A] = [ A]o − kt ln[ A] = ln[ A]o − kt ptot = ∑ pi i 1 1 = + kt [ A] [ A]o x i pio w = − Pext ΔV ΔS = q T p xi = i ptot o ΔS rxn pi = ΔH o Δ S o ln K p = − + RT R − b ± b 2 − 4ac x= 2a = ∑ p S (products) − o products ∑ reac tan ts r S (reactants) o ΔGrxn = o ΔE = q + w k= −E a Ae RT ∑ pΔ G o (products) − products ∑ reac tan ts r ΔG o (reactants) ΔG = ΔH − TΔS r1 M2 = r2 M1 E = hν o ΔGrxn = − RT ln K E K = 3 2 RT Π = iCRT o ΔH rxn = products ∑ pΔ H o (products) − f reac tan ts ∑ r ΔH o (reactants) f ΔS = ΔH fus T ΔH = ΔE + pΔV pV = nRT ΔHvap T ΔG = ΔG o + RT ln Q ΔG o = − nFE o q = CΔT ΔS = ⎛ n2 a ⎞ ⎜p+ ⎟(V − nb) = nRT ΔTf = ik f m ΔTb = ik b m 2⎟ ⎜ V⎠ ⎝ F .C . = # valence electrons − (non − bonding electrons) − 1 / 2 (shared electrons) RT ln Q E=E − nF o CHEM 1800 ‐ FORMULA AND DATA SHEET (part 2) 1 atm = 760 mmHg = 101.325 kPa = 1.01325 bar ln 2 1 ∆ 1 2 1 1 ln 2 1 ∆ . 1 2 1 1 ln E log ...
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This note was uploaded on 11/11/2010 for the course CHEMISTRY CHEM1800 taught by Professor Krista during the Winter '10 term at UOIT.

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