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chem1a-unknown99-final-unknown-soln - Part 1 Multiple...

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Unformatted text preview: Part 1: Multiple Choice. (5 pts each, 145 pts total) Instructions: Bubble in the correct answer on your Scantron™ form AND circle the answer on your exam. Each question has one correct answer. 1.) The answer to question 1 is A. Bubble in A on your Scantron™ form. 2.) Hydrogen has two stable isotopes, 1H and 2H, and nitrogen has two stable isotopes, 14N and 15N. Which isotopic species of ammonia will give a peak at mass 19 in a mass spectrometer? A.) 14N1H22H 3.) B.) Ti2O3 B.) 3.7 × 1012 B.) 50 K C.) Ti3O2 D.) Ti2O E.) TiO2 C.) 4.11 × 1012 D.) 5.4 × 1021 E.) 1.2 × 1023 C.) 71 K D.) 141 K E.) 400 K HA1 and HA2 are two weak acids with dissociation constants KA1 and KA2, respectively. If the equilibrium constant for the reaction, HA1 + A2– HA2 + A1– is K > 1, which of the following must be true? A.) KA1 = KA2 B.) KA1 > KA2 C.) KA1 < KA2 E.) KA1 × KA2 = Kw D.) KA1/ KA2 = Kw 7.) E.) 15N1H3 For O2 molecules at 100 K, vrms = 8.8 m/sec. At what temperature does vrms = 4.4 m/sec? A.) 25 K 6.) D.) 15N1H2H2 The vapor pressure of tungsten at 2500 °C is 7.0×10-9 atm. What is the number of gaseous tungsten atoms in a light bulb of volume 0.20 L operating at 2500 °C? A.) 1.9 × 1010 5.) C.) 14N1H2H2 An oxide of titanium contains 40% oxygen by weight. What is the empirical formula of titanium oxide? A.) TiO 4.) B.) 14N2H3 A solution of NaOH with pH = 10.00 is diluted with H2O by a factor of 10. The resulting pH is: A.) 1.00 B.) 9.00 C.) 9.43 D.) 10.57 E.) 11.00 Page 2 of 11 8.) A solution of NH3 with pH=10.00 is diluted with H2O by a factor of 10. The resulting pH is: A.) 1.00 9.) C.) H2O D.) NaCl E.) NH3 B.) N2 C.) O2 D.) CO2 E.) NH3 B.) Cl– C.) Ar D.) K+ E.) Ca2+ B.) Cl C.) Ar D.) K E.) Ca B.) O2– C.) Rb D.) Al E.) S– Which atom or ion can have the following electron configuration 1s22s22p63s23p54s1? A.) Ar 15.) B.) NaOH Which of the following ground state atoms or ions is not paramagnetic? A.) F 14.) E.) 11.00 Which of the following has the highest ionization energy? A.) S 13.) D.) 10.57 Which of the following has the smallest atomic or ionic radius? A.) S2– 12.) C.) 9.43 A 0.1 M solution of which of the following species has the highest pressure of that species above the solution? A.) He 11.) B.) 9.00 Which compound could be added to the solution of sodium acetate (CH3COONa) in order to make an acidic buffer? A.) HCl 10.) Name: _________________________________________ B.) K C.) Ca+ D.) Ti2+ E.) Zn In which of the following orbitals is the electron probability density spherically symmetric, i.e. independent of the angles ϕ and θ? A.) 9s B.) 8p C.) 7d D.) 6f E.) 5g Page 3 of 11 16.) For a neutral hydrogen atom, the radiation absorbed in the transition from n = 2 to n = 3 corresponds to a wavelength of 657 nm. What would be the wavelength of radiation absorbed in the transition from n =1 to n = 3? A.) 103 nm 17.) B.) ON O E.) He 1s1 4p1 C.) N N D.) O C O E.) H N H H B.) 90° C.) 109.5° D.) 120° E.) 180° B.) CH2Cl2 D.) CO E.) CS2 C.) CH3Cl B.) red C.) green B.) q > 0 C.) ∆S < 0 Which is true for the following spontaneous reaction? CH3OH (l) + 3/2 O2 (g) A.) ∆H° > 0 24.) D.) He 1s1 2p1 C.) He+ 2s1 D.) blue E.) ultraviolet One mole of an ideal gas is compressed isothermally. Which of the following inequalities is true? A.) ∆P < 0 23.) B.) He+ 4s1 For a certain metal, orange light does not eject electrons, but yellow light does. Light of which range will eject electrons from the same metal with the lowest kinetic energy? A.) infrared 22.) E.) 4205 nm Which molecule does not have an electric dipole moment? A.) CHCl3 21.) D.) 1314 nm What is the H–C–H angle in CH3+? A.) 60° 20.) C.) 1051 nm Which one of the following is an incorrect Lewis electron dot structure? A.) H C N 19.) B.) 657 nm Which of the following has the lowest ionization energy? A.) He+ 1s1 18.) Name: _________________________________________ B.) ∆H° = 0 C.) ∆H° < 0 D.) ∆V > 0 E.) ∆T < 0 CO2 (g) + 2 H2O (l) D.) ∆S° > 0 E.) ∆G° > 0 Given that EO=O > 2 EO–O where the E’s refer to bond energies, which is true for the conversion of ozone to oxygen? 2 O3 3 O2 A.) ∆H° > 0 B.) ∆H° = 0 C.) ∆H° < 0 D.) ∆S° < 0 E.) ∆G° > 0 Page 4 of 11 Name: _________________________________________ For each of the problems 25-30, select the graph that best describes the behavior listed. A.) B.) 0 25.) 0 0 0 0 B.) B C.) C D.) D E.) E B.) B C.) C D.) D E.) E B.) B C.) C D.) D E.) E B.) B C.) C D.) D E.) E The kinetic energy of photoelectrons (Ekin) as a function of 1/λ where λ is the wavelength of the light impinging on Cs metal. A.) A 30.) 0 0 The kinetic energy of an ideal gas (Ekin) as a function of T (K). A.) A 29.) 0 ln(K) as a function of 1/T for the combustion of C (s) to CO (g). A.) A 28.) 0 E.) PV as a function of T (°C) for an ideal gas. A.) A 27.) 0 D.) Solubility of Mg(OH)2 as a function of [H3O+]. A.) A 26.) C.) B.) B C.) C D.) D E.) E The solubility of O2 (g) in H2O (l) as a function of PO2 at low pressure. A.) A B.) B C.) C D.) D E.) E Page 5 of 11 Name: _________________________________________ Part 2: Short Answer Problems (205 pts total) Instructions: Enter answers in the boxes provided. Show your work. Explain your answer when requested in 15 words or less. (10 pts) 1.) Hypochlorous acid, HClO, can be formed from the following chemical reaction. Balance the chemical reaction. 2 Cl2 + 1 O2 + 2 H2O ! 4 HClO If 4 moles Cl2, 2 moles O2, and 1 mole H2O are mixed and the reaction proceeds until one or more of the reactants is completely consumed, how many moles of hypochlorous acid will be produced? Answer: 2 moles (15 pts) 2.) A 10.0 L bulb is maintained at 30.0 °C. After evacuating, 1.00 g H2O (g) is injected into the bulb. a) If the water vapor acts like an ideal gas, what is the pressure inside the bulb? P V = n R T, P = n R T / V = 0.138 atm Answer: 0.138 atm b) Given the vapor pressure of H2O at 30.0 °C is 0.0418 atm. Compare this value to your answer in part a). Describe what happens in the bulb. (Use 15 words or less.) 0.0418 < 0.138 Answer: 0.0418 atm < 0.138 atm. Q > K for H2O(l) -> H2O(g), so the water vapor consenses. Page 6 of 11 Name: _________________________________________ (16 pts) 3.) Draw the Lewis electron dot structure and sketch the molecular geometry of PCl3 and IF2–. PCl3 IF2– Lewis electron dot structure Molecular geometry Lewis electron dot structure Molecular geometry (14 pts) 4.) Given: 2 C2H2 (g) + 5 O2 (g) 4 CO2 (g) + 2 H2O (l) ∆H = -2602 kJ r4 4 CO2 (g) + 6 H2O (l) 2 C2H6 (g) + 7 O2 (g) ∆H = -3123 kJ r4 H2 (g) + 1/2 O2 (g) H2O (l) ∆H = -286 kJ r4 34545 34535 What is the ∆H for the following reaction at 25 °C and 1 atm? C2H2 (g) + 2 H2 (g) C2H6 (g) Answer: –311.5 kJ (12 pts) 5.) 1000 mL of an ideal gas is compressed to 500 mL under a constant external pressure of 10 atm. During the compression, 500 J of heat flowed from the gas to the surroundings. What are q and w for the process, and ∆E for the gas? q= w= –500 J ∆E = 507 J 7J Page 7 of 11 Name: _________________________________________ (20 pts) 6.) What is the pH of each of the following solutions? a) 0.10 M acetic acid (CH3COOH) Answer: 2.88 b) 0.10 M sodium acetate (CH3COONa) Answer: 8.88 c) A mixture prepared by adding 500 mL of solution (a) to 500 mL of solution (c). Answer: 4.75 (10 pts) 7.) Arrange the solutions in order of increasing pH. Place the appropriate letters in the boxes. (no pH calculations are needed) A.) 0.2 M NaCl D B.) 0.2 M CH3COONa < C < C.) 0.2 M NH4Cl A < D.) 0.2 M HCl B < E.) 0.2 M NaOH E Page 8 of 11 Name: _________________________________________ (12 pts) 8.) 500 mL of a 2.0 × 10-3 M AgNO3 solution are added to 500 mL of a 2.0 × 10-5 M NaCl solution. Determine whether or not a precipitate will form? Justify your answer. Ksp = 1.8 × 10–10 Q = [Ag+][Cl–] = (1.0 × 10–3 M)(1.0 × 10–5 M) = 1 × 10–8 Q > K, therefore a precipitate will form. Answer: Yes, a precipitate will form. (14 pts) 9.) The extinction coefficient (ε) with units of cm2/g equals the absorbance (A) for a 1 g/mL solution for a path length (Ρ) of 1.00 cm. a) If an ethanol blank gives an intensity (I) of 2.0 µA at 400 nm and a 1 g/mL sample of Z dissolved in ethanol gives an intensity of 1.5 µA, what is the extinction coefficient for Z at 400 nm? A = –log(Io/I) Answer: 0.125 cm2/g b) The absorbance of a solution containing Z dissolved in ethanol is determined to be 0.40. What is the concentration of Z in the solution? A=εℓc Answer: 3.2 g/mL Page 9 of 11 Name: _________________________________________ (14 pts) 10.) An air sample obtained on top of a mountain has a density of 1.00 g/L at 0.80 atm and 280 K. Calculate the mole fractions of oxygen and nitrogen in the air sample, assuming only nitrogen and oxygen are present and the gases are ideal under these conditions. Answer: 0.82 N2 0.18 O2 (20 pts) 11.) Consider the following reaction: PbO2 (s) a) Pb(s) + O2 (g) Calculate ∆G° for the reaction. ∆Gº = ∆Hº – T∆Sº Answer: 217 kJ/mole b) Calculate the equilibrium constant for this reaction at 25 °C. ∆Gº = –R T lnK K = e–∆Gº/RT = 1.33 × 10–39 Answer: 10–39 c) Circle the temperature(s) at which the reaction is spontaneous at standard pressures and concentrations. Place an ‘X’ over (cross out) the temperature(s) at which the reaction is not spontaneous. Show your work. ∆G = 0 ∆H = T∆S ∆H / ∆S = T 500 K 1000 K Page 10 of 11 Name: _________________________________________ (14 pts) 12.) Using average bond energies, estimate the change in enthalpy, ∆H, of the following (unbalanced) reaction. CO (g) + O2 (g) CO2 (g) ∆Hrxn = ΣHbonds broken – ΣHbonds formed Answer: –323 kJ/mole O2 (14 pts) 13.) The emission from level 3 to level 2 corresponds to a photon wavelength of 800 nm; this line is indicated on the spectrum below. Sketch and label with appropriate wavelengths and transitions the remaining line(s) on the spectrum. E3!2 = hc/800nm E2!1 = 2E3!2 = 2 hc/800nm = hc/400nm E3!1 = E2!1 + E3!1 = (hc/800nm) + (hc/400nm) = 3 hc/800nm = hc/267 nm Spectrum 3 3!1 267nm 0 2 2!1 400nm 500 1000 1500 2000 2500 λ (nm) Page 11 of 11 Name: _________________________________________ (20 pts) 14.) Consider the molecule O2 and the molecular ion O2+ in their respective ground states. a) Fill in the electrons for the molecular orbital diagrams for O2 and O2+. σ* 2pz π* 2p σ* 2pz π* 2p π2p σ2p π2p σ2p σ* 2s σ* 2s σ2s σ2s z z O2+ O2 b) Determine the bond orders for O2 and O2+. O2+: O2: 2 2½ c) Upon the ionization of O2, how does the bond strength change? Circle the correct response. decreases does not change increases d) Upon the ionization of O2, how does the paramagnetism change? Circle the correct response. decreases does not change increases ...
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