Sample Final Examination Chemistry 217

Transcription

1 Sample Final Examination Chemistry 217 Multiple-choice Questions (2 marks each) Circle the appropriate response. 1. A sky-blue aqueous solution was labeled "chromium(ii) perchlorate". This solution contains the ions A) Cr 2 O 2+ and ClO 4. B) Cr 2 O 4+ and Cl. C) Cr 2+ and Cl. D) Cr 2+ and ClO 4. E) Cr 3+ and ClO A green compound composed of chromium and oxygen contains 68.42% Cr. What is the empirical formula of the compound? A) Cr 3 O B) Cr 2 O 3 C) CrO 3 D) Cr 2 O E) Cr 2 O 2 3. The F F bond length in F 2 (g) is 1.42 Å. If 1 Å = m, what is the bond length in pm? A) 14.2 pm B) 71 pm C) 1420 pm D) 142 pm E) pm 4. If an aqueous solution of sulfuric acid is added to a pool of mercury, SO 2 (aq) and mercury(ii) sulfate are formed. Which species is reduced? A) H 2 SO 4 (aq) B) Hg(l) C) H 2 O(l) D) SO 2 (aq) E) HgSO 4 (aq)

2 5. When BaO(s) dissolves in water, A) the resulting solution is acidic. B) hydrogen gas is produced. C) O 2 (aq) reacts with water to give hydroxide ions. D) the resulting solution is neutral. E) oxygen gas is produced. 6. Consider the following reactions. ZrC(s) + 4Cl 2 (g) ZrCl 4 (g) + CCl 4 (g) ZrCl 4 (g) + 2Mg(s) Zr(s) + 2MgCl 2 (l) How many moles of Zr(s) are produced from 9.00 moles of chlorine gas? A) 2.25 mol B) 1.00 mol C) mol D) 9.00 mol E) 2.00 mol 7. How many moles of sodium sulfate must be added to an aqueous solution that contains 2.0 moles of barium chloride in order to precipitate 2.0 moles of barium sulfate? A) 1.0 mol B) 2.0 mol C) Not enough barium chloride is available to precipitate 2.0 moles of barium sulfate. D) 3.0 mol E) 1.5 mol 8. Consider the following reaction. 4NH 4 ClO 4 (s) 2Cl 2 (g) + 8H 2 O(g) + 2N 2 O(g) + 3O 2 (g) Calculate the total volume of all gases produced at STP by the decomposition of 5.50 moles of ammonium perchlorate. A) 20.6 L B) 14.7 L C) 123 L D) 462 L E) 8.21 L 9. The pressure of a gas in a rigid container at 18 o C is 745 Torr. What is the pressure of the gas at 75 o C? A) 285 Torr B) 1100 Torr C) 760 Torr D) 77.3 Torr E) 507 Torr

3 10. Calculate the reaction enthalpy for 2S(s) + 3O 2 (g) 2SO 3 (g) from the data SO 3 (g) S(s) + 3/2O 2 (g) A) kj B) kj C) kj D) kj E) kj H o = kj 11. If 100 ml of 1.00 M silver nitrate are added to 100 ml of 1.00 M potassium iodide in a calorimeter with a heat capacity of 2.30 kj/k, the temperature rises 4.87 K. Calculate the enthalpy change for Ag + (aq) + I (aq) AgI(s) A) 9.45 kj B) 4.72 kj C) 21.2 kj D) 56.0 kj E) 112 kj 12. Which of the following represents the first electron affinity of oxygen? A) O(g) + 2e (g) O 2 (g) B) O(g) + e (g) O (g) C) O(g) O + (g) + e (g) D) O(s) + e (g) O (g) E) O(s) + 2e O 2 (g) 13. What is the valence-electron configuration of the alkaline earth elements? A) np 2 B) ns 2 C) np 1 D) ns 1 E) ns 2 np 1

4 14. Calculate the energy per photon of radio waves of frequency 92.1 MHz. Planck's constant is J s. A) J B) J C) J D) J E) J 15. How many lone pairs of electrons does the iodide atom possess in the Lewis structure of HI? A) 3 B) 2 C) 1 D) 6 E) How many lone pairs are there in the Lewis structure of dinitrogen tetroxide, O 2 N NO 2? A) 10 B) 12 C) 8 D) 4 E) How many valence electrons are there in the carbonate ion, CO 3 2? A) 24 B) 26 C) 22 D) 18 E) What type of orbitals are used to form the N N bond in hydrazine, N 2 H 4? A) sp 3 sp 3 B) sp sp C) sp sp 3 D) sp sp 2 E) sp 2 sp 2

5 19. The O N O bond angle in NO 3 is A) equal to 90 o or 180 o. B) <109 o. C) equal to 90 o or 120 o. D) equal to 120 o. E) much less than 120 o. 20. Consider the following: (1) C 2 H 4 ; (2) C 2 H 2 ; (3) C 6 H 6 List the carbon-carbon bonds in order of decreasing average bond enthalpy. A) (2) > (3) > (1) B) (1) > (2) > (3) C) (3) > (1) > (2) D) (3) > (2) > (1) E) (2) > (1) > (3) 21. In which of the following would the boiling point of water be lowest? A) in New York city where the pressure is about 760 Torr B) in a pressure cooker where the pressure is 1400 Torr C) in the "mile high" city of Denver D) in New Mexico where the pressure is about 710 Torr E) at the peak of Mt. Everest 22. The phase diagram for a pure substance is given below.

6 The substance is stored in a container at 150 atm at 25 o C. Describe what happens if the container is opened at 25 o C. A) The liquid in the container vaporizes. B) The solid in the container sublimes. C) The liquid in the container freezes. D) The solid in the container melts. E) The vapor in the container escapes. 23. List the following in order of increasing boiling point: hydrogen chloride, hydrogen fluoride, argon A) HF < Ar < HCl B) Ar < HCl < HF C) Ar < HF < HCl D) HCl < Ar < HF E) HF < HCl < Ar 24. Calculate the freezing point of a 7.0 m aqueous solution of ethylene glycol. The k f for water is 1.86 K kg mol 1. A) 13 o C B) 3.8 o C C) 26 o C D) 0 o C E) 0.27 o C 25. Calculate the molality of methanol in a bottle of "methyl hydrate" used to help start automobiles on damp days, if the solution is 90.0% CH 3 OH by mass. The molar mass of methanol is 32.0 g mol 1. A) m B) 28.8 m C) 2.81 m D) m E) 281 m 26. Calculate the vapor pressure at 25 o C of a mixture of benzene and toluene in which the mole fraction of benzene is The vapor pressure at 25 o C of benzene is 94.6 Torr and that of toluene is 29.1 Torr. A) 81.5 Torr B) 69.9 Torr C) 105 Torr D) 75.7 T0rr E) 124 Torr

7 Short-answer Questions (4 marks each) 27. If the standard enthalpy of combustion of cyclohexane, C 6 H 12 (g), is 3953 kj mol 1, how many liters of cyclohexane measured at 25 o C and kpa must be burned to liberate kj of heat? 28. The absorbance of a dye at 660 nm in a 1 cm cell is If the concentration of the dye is M, calculate the molar absorption coefficient of the dye. Describe the color and intensity of the solution of the dye. 29. Given the following data, calculate the second electron affinity of oxygen. enthalpy of formation of Ca(g): 178 kj mol 1 first ionization energy of Ca(g): 590 kj mol 1 second ionization energy of Ca(g): 1150 kj mol 1 enthalpy of formation of O(g): 249 kj mol 1 first electron affinity of O(g): -141 kj mol 1 lattice enthalpy of CaO(s): 3505 kj mol 1 enthalpy of formation of CaO(s): 635 kj mol Describe the bonding in acetonitrile, CH 3 CN. 31. Rhodium has a density of 12.4 g cm 3 and an atomic radius of 134 pm. What is the structure of the solid? 32. The addition of 1.96 g of vitamin B 12, isolated as cyanocobalamin, to 100 g camphor lowers the freezing point by 0.57 o C. What is the molar mass of vitamin B 12? The k f for camphor is 39.7 K kg mol 1. Long-answer Questions (6 marks each) 33. Draw the Lewis structure of XeF 6 and predict this molecule's shape using VSEPR theory. What are the bond angles? 34. Potassium chloride has an NaCl-type cyrstal structure. If the density of potassium chloride is g/cm 3, determine the length of an edge of the unit cell.

8 35. Explain FIVE of the following terms and give examples where appropriate to illustrate your definition. a. VSEPR b. dipole moment c. resonance d. Boyle's Law e. partial pressure f. ppm g. Henry's Law 36. Cobalt(II)chloride exists as a hydrated salt that can be represented by the formula CoCl 2. xh 2 O. In an experiment to determine the exact formula of this hydrated salt, g of the hydrate was dissolved in 250 ml of water and excess sodium hydroxide was added to the resulting solution. The reaction that occured produced g of cobalt(ii)hydroxide. Determine the formula of hydrated cobalt(ii)hydroxide (i.e. the value of x in CoCl 2. xh 2 O) *** END OF EXAMINIATION ***

9 Final Examination Chemistry 217 Answer Key 1. D 2. B 3. D 4. A 5. C 6. A 7. B 8. D 9. E 10. E 11. E 12. B 13. B 14. B 15. A 16. A 17. A 18. A 19. D 20. E 21. E 22. A 23. B 24. A 25. E 26. A 27. Moles cyclohexane = (1000 kj)/(3953 kj/mol) = mol Volume cyclohexane = nrt/p = ( mol)(0.0821)(298 K)/(107.2/101.3 atm) = 5.85 L 28. A = C (conc)(path length) = C ( M)(1 cm) C = 1.41 x nm absorbs in red therefore expect blue/green colour. A is large therefore very intense colour.

10 29. O - (g) ====> O 2- (g)? O(g) ====> O - (g) /2O 2 (g) ====> O(g) 249 Ca + (g) ====> Ca 2+ (g) 1150 Ca(g) ====> Ca + (g) 590 Ca(s) ====> Ca(g) 178 CaO(s) ====> Ca(s) + 1/2O 2 (g) 635 CaO(s) ====> Ca 2+ (g) + O 2- (g) 3505? = 844 kj/mol 30. sigma single bonds for all C-H and C-C using sp 3 orbitals on the methyl carbon and sp orbitals on the central carbon one sigma bond C-N using sp orbitals on carbon and nitrogen two pi bonds C-N using 2 p orbitals on carbon and nitrogen 31. Assume fcc and try. Volume = (8 1/2 r) 3 = (8 3/2 )(1.34 x 10-8 cm) 3 = 5.44 x cm 3 Mass of one Rh atom = (102.9 g/mol)/(6.022 x atoms/mol) = x g Density = 4(1.709 x g)/(5.44 x cm 3 ) = 12.5 g/cm 3 Therefore it is face-centred cubic structure 32. T = ik f x molality 0.57 o C = (1)(39.7 K kg/mol)(molality) molality = x 10-2 mol/kg = (1.96 g/mwt (B 12 ))/0.100 kg) MWt(B12) = 1365 g/mol 33. F 6 Xe: Shape based on a pentagonal bipyramid--distorted octehedral All 90 o KCl per unit cell Wt of 4KCl = 4(39.1 g/mol g/mol)/6.023 x = x g Volume = ( x g)/(1.984 g/cm 3 ) = x cm 3 Edge Length = (Volume) 1/3 = 6.29 x 10-8 cm or 6.29 A

11 35. a. VSEPR - valence-shell electron-pair repulsion model to predict geometric "shape" around a central atom b. diplole moment - a measure of separation between positive and negative centres in polar molecules c. resonance - 2 or more structures describing a molecule where the average gives a real description d. Boyle's Law - at constant T PV is a constant e. partial pressure - pressure exerted by a particular gas in a mixture f. ppm - part per million g. Henry's Law - concentration of a gas in a solution is proportional to the pressure of the gas over the solution (Cg = kpg) g of Co(OH) 2 ===> 6.16 x 10-3 moles Moles of CoCl 2. xh 2 O = Moles of Co(OH) 2 MWt (CoCl 2. xh 2 O) = (1.024 g)/(6.16 x 10-3 moles) = g/mol CoCl 2. xh 2 O = xh 2 O = 36.2 x = 36.2/18 = 2 CoCl2. 2H2O