Department of Chemistry Memorial University of Newfoundland Chemistry 1050 Fall 2012 Final Examination Time 3 hours NAME: MUN Student Number: Circle your professor s name. Robert Davis Christopher Flinn Peter Warburton Read the Following Carefully 1. This examination has 12 pages. Questions are on pages 2 through 12 and a periodic table is on page 13. Ensure that all pages for this examination paper are present. 2. A sheet containing the periodic table, physical constants and some equations which may be useful to you are provided. These are on the last sheet of the examination paper and may be detached for use. 3. Failure to submit this paper in its entirety at the end of the examination will normally result in disqualification. 4. Answer each question in the space provided. 5. Show all relevant calculations and justify simplifying assumptions. 6. Numerical answers should be reported to the appropriate number of significant digits with the correct units. Do NOT write in the table below. Question Value Mark 1 4 9 5 9 12 10 5 11 12 8 13 14 9 15 16 12 17 19 9 20 21 12 22 24 10 25 7 26 27 7 Total 100-1 -
[2] 1. A 4.00 L sample of argon at 40.5 ºC is cooled at constant pressure to reduce its volume to 1.00 L. What is the new temperature of the argon? [2] 2. A sample of neon is compressed from a volume of 65.0 L to a volume of 13.0 L by an external pressure of 12.0 bar at constant temperature. The neon gains 17.4 kj of heat. Calculate U for the neon gas. [3] 3. A fixed volume of carbon dioxide gas takes 136 s to effuse through a pinhole. The same volume of a Noble gas takes 234.9 s. Identify the Noble gas. [2] 4. Calculate the density of chlorine gas at 32.5 ºC and 2.56 atm pressure. - 2 -
[4] 5. Write ground state electron configurations for the following species: P Cr Br Ni 2+ [2] 6. Calculate the wavelength in picometers (1 pm = 10 12 m) of an electron travelling at 25.0 % of the speed of light. The mass of an electron is 9.109 x 10 28 g. [2] 7. Arrange the following ions in order of increasing size. Briefly give your reasoning. F, Cl, Mg 2+ [2] 8. Define or give a brief explanation for the following: (a) Enthalpy is a state function. (b) The lattice enthalpy of an ionic compound e.g. NaCl. (c) The Pauli Exclusion principle. [2] 9. What is the significance of a node in a wavefunction (orbital node)? Distinguish between radial and angular nodes. - 3 -
[5] 10. Consider the phase diagram for CO2 below: D 73 X I III P(atm) A B 1-78.5 C Complete the following: T(ºC) II 31.1 (a) (b) What phase exists at point X? answer: What is the significance of the triple point? Clearly mark its location on the diagram above using an arrow and the letter T. (c) What phase changes occur along isotherm CD as the pressure is raised? (d) What phase changes occur along isobar AB as the temperature is raised? (e) What is the effect of increasing external pressure on the melting point of CO2? (f) Can CO2(g) be liquefied using pressure at temperatures above 31.1ºC? Briefly explain. - 4 -
[4] 11. A 100.0 ml volume of 1.50 mol L 1 Cl(aq) is mixed with 50.0 ml of 3.00 mol L 1 NaO(aq) in a Styrofoam cup calorimeter, both solutions initially at 22.5ºC. Calculate the final temperature reached, assuming that the density of the solutions is 1.00 g ml 1 and the specific heat of the final solution is 4.184 J g 1 ºC 1. What other assumptions need to be made? NaO(aq) + Cl(aq) NaCl(aq) + 2O(l) = 36.5 kj mol 1 Cl [4] 12. A 3.1995 g sample of ammonia is burned in a constant volume bomb calorimeter containing excess oxygen. The calorimeter has a heat capacity of 17.42 kj C -1. The temperature of the calorimeter increases from 25.000 C to 28.120ºC. Determine the internal energy of combustion U and the enthalpy of combustion for the following equation as written at 25.00ºC. 4 N3(g) + 5 O2(g) 4 NO(g) + 6 2O(l) - 5 -
[4] 13. The electron in the hydrogen like species Li 2+ can absorb a photon promoting it to an allowed higher energy excited state from the ground state. Determine the wavelength in nanometers of the photon if the electron is promoted to its third excited state. [5] 14. Use valence bond theory to describe the bonding in A complete answer includes: C N The hybridization scheme of the carbon and nitrogen atoms and the type of orbital used by the hydrogen atoms for bonding. A sketch of the orbitals used for bonding by carbon, nitrogen and hydrogen showing how they overlap to form bonds. Label each bond formed as either (sigma) or (pi). - 6 -
[8] 15. Complete the following table: 2CO BrF5 Draw the best Lewis structure Name the molecular shape. Sketch the molecular shape (include your predicted bond angles). Indicate whether the molecule is polar or non polar. [4] 16. Draw all equivalent resonance structures for the carbonate ion CO3 2 and the resonance hybrid. Assign formal charges to all atoms. Estimate the bond dissociation energy of the carbon to oxygen bonds given D (C=O) = 736 kj mol 1 and D (C O) = 380 kj mol 1. - 7 -
[3] 17. Complete the valence energy level diagram below for O2 below Indicate the correct bond order for each species and indicate whether it is paramagnetic or diamagnetic. species * * * * Energy * 2s 2s * 2s 2s bond order magnetic property [2] 18. Predict which species, O2 + or O2, will have the greater bond dissociation energy. Briefly explain your choice. Refer to your answer for 17. [4] 19. Use ess s law to calculate º for the reaction: Given: 2 C4(g) C24(g) + 2 2(g) 2 C26(g) + 7 O2(g) 4 CO2(g) + 6 2O(l) º = 3119.4 kj C4(g) + 2 O2(g) CO2(g) + 2 2O(l) º = 890.3 kj C24(g) + 2(g) C26(g) º = 137.0 kj 2 2(g) + O2(g) 2 2O(l) º = 571.6 kj - 8 -
[6] 20. Give brief explanations for the following based on the intermolecular forces involved. (a) Dimethyl ether C O C has a higher boiling point than propane C C C (b) CBr4 has a higher boiling point than CCl4. (c) N3 has a higher boiling point than P3. [6] 21. Give brief explanations for the following. (a) Atomic radius decreases across a period (left to right). (b) The second ionization energy of nitrogen is greater than its first ionization energy. (c) The effective nuclear charge on the valence electrons in a group of the periodic table is approximately constant. - 9 -
[4] 22. A 0.944 mol L 1 solution of glucose, C612O6, in water has a density of 1.0624 g ml 1 at 20ºC. Calculate the mole fraction of glucose in the solution. [3] 23. Dimethyl ether has a vapor pressure of 400.0 mmg at 17.9ºC and a molar enthalpy of vaporization of 28.6 kj mol 1. Determine the normal boiling point of dimethyl ether. [3] 24. An ideal mixture of CCl3 and C2Cl2 at 25ºC has a mole fraction of CCl3 in the solution of 0.600. The vapor pressures of pure liquid CCl3 and pure liquid C2Cl2 at 25ºC are 118 mmg and 285 mmg respectively. What is the mole fraction of CCl3 in the vapor phase above the solution? - 10 -
[3] 25. (a) A compound that contains only carbon and hydrogen was burned in excess O2 to give CO2 and 2O. When 0.2704 g of the compound was burned, the CO2 produced reacted completely with 20.0 ml of 2.00 mol L 1 NaO(aq) according to the following equation. CO2(g) + 2 NaO(aq) Na2CO3(aq) + 2O(l) Determine the empirical formula of the compound. [4] (b) When a 0.544 g sample of the same hydrocarbon from part(a) was dissolved in 50.0 g of camphor, the resulting solution has a freezing point of 176.0ºC. Pure camphor freezes at 179.8ºC and has a molal freezing point depression constant Kf = 37.7 K kg mol 1. Determine the molar mass and the molecular formula of the hydrocarbon. - 11 -
[5] 26. The lab bottle of oxalic acid dihydrate 2C2O4 2 2O was found to be contaminated with NaCl. A 0.2500 g sample of the impure oxalic acid dihydrate was completely consumed in excess acidified KMnO4(aq), yielding 95.76 ml of CO2(g) collected by downward displacement of water at 20.0ºC and a total (barometric) pressure of 101.47 kpa. The vapor pressure of water at 20ºC is 17.54 mmg. Determine the % of oxalic acid dihydrate by mass in the lab bottle assuming the contamination is homogenous. 5 2 C 2 O 4 2 2 O(s) + 2 KMnO 4 (aq) + 6 Cl(aq) 10 CO 2 (g) + 2 MnCl 2 (aq) + 2 KCl(aq) + 10 2 O(l) [2] 27. Calculate the osmotic pressure in bar of a 0.150 mol L 1 aqueous solution of Fe(NO3)3 at 25ºC. - 12 -