Test 4 first letter of last name Chemistry 12 Dr. Kline 7 December 2005 Name This test consists of a combination of multiple choice and other questions. There should be a total of 22 questions on eight pages; please check to make sure that they are all here. You may use the equation/information sheet and any periodic table provided (on page 9). Do not use your own tables, scratch paper or other information. Do not share your calculator. Please turn off all cell phones, pagers and other communication devices; if they make noise, they will be confiscated. Shared calculators will be confiscated. Multiple Choice Questions Each of the following 15 questions is worth three points, for a total of 45 points. It is not necessary to show work for these questions; however, you may write on the exam. Answer each question by circling the letter(s) corresponding to the correct choice(s). Unless it is stated otherwise in a given problem, there is only one correct answer for each question. In questions where it states that more than one answer is possible, there may be one or more correct answers: please circle all of the correct answers. 1. Which of the following processes is/are endothermic? More than one answer may be correct. a. sublimation of caffeine b. condensation of steam to liquid water c. melting of para-dichlorobenzene 2. Suppose that 0.100 g of liquid benzene, C 6 H 6, is at 20. C in a closed container that is fitted with a piston that can be used to adjust the volume. The piston is then pulled up until the volume of the container is equal to 350 ml. What is the pressure due to the benzene vapor, still at 20. C? The vapor pressure of benzene is 80.85 mmhg at 20. C and its molecular weight is 78.1 g/mole. a. P < 80.85 mmhg b. P > 80.85 mmhg c. P = 80.85 mmhg d. It is impossible to tell 3. Which of the following substances is expected to be the least soluble in water? a. CH 3 CH 2 CH 2 CH 2 OH b. CH 3 CH 2 OCH 2 CH 3 c. CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 d. it is impossible to tell 4. Which of the following aqueous solutions has the lowest vapor pressure at 25 C? a. 0.10 M glucose, C 6 H 12 O 6 b. 0.20 M sucrose, C 12 H 22 O 11 c. 0.30 M fructose, C 6 H 12 O 6 d. it is impossible to tell because they all contain different solutes 5. Which of the following aqueous solutions has the highest melting point? Assume theoretical van t Hoff values (i). a. 0.15 m KCl b. 0.10 m FeCl 3 c. 0.25 m CaCl 2 d. 0.30 m NH 4 Cl Chem 12 Test 4B page 1 of 6
6. Which of the following 0.10 M aqueous solutions has the lowest melting point? Assume theoretical van t Hoff values (i). a. K 2 [CuCl 4 ] b. K 4 [Mn(CN) 6 ] c. [Co(NH 3 ) 4 (NO 2 ) 2 ]Cl d. [Cr(NH 3 ) 6 ](ClO 4 ) 3 e. it is impossible to tell 7. Which of the following saturated aqueous solutions has the greatest osmotic pressure at 25 C? The K sp values given are for each solute. a. Zn(IO 3 ) 2 (K sp = 3.9x10-6 ) b. PbI 2 (K sp = 7.9x10-9 ) c. Ag 2 CrO 4 (K sp = 2.6x10-12 ) d. it is impossible to tell 8. Consider two aqueous solutions of sucrose, C 12 H 22 O 11, at 25 C, one saturated and the other unsaturated. The vapor pressure of both solutions is measured. Then, the lids are removed and some water is allowed to evaporate from both solutions. The lids are then replaced and the vapor pressures are again measured. Which solution has a different vapor pressure now than it did before? a. the saturated one b. the unsaturated one c. both solutions d. neither solution e. it is impossible to tell 9. When a certain ionic compound is dissolved in water, the temperature of the solution decreases as compared to the original water. Which of the following statements is/are true regarding this dissolving process? More than one answer may be correct. a. The enthalpy of solution, H soln, is negative. b. The entropy of solution, S soln, is negative. c. The enthalpy of hydration, H hyd, is negative. d. None of them 10. A solution consisting of a nonvolatile, covalent (non-electrolyte) compound dissolved in water is placed in a tube with a semipermeable membrane on one end. This tube is placed in a beaker of pure water. What happens? a. The compound will flow from the tube to the beaker. b. Water will flow from the tube to the beaker. c. Water will flow from the beaker to the tube. d. Nothing will move either way Chem 12 Test 4B page 2 of 6
Use the following van t Hoff plot for acetone and 2-propanol to answer the two questions that follow. The equation that s plotted for the graph is ln(p vap ) = ( H vap /R)(1/T) + ln( S vap )/R 11. What is the estimated normal boiling point of 2-propanol? a. 100 C b. 50 C c. 85 C d. 30 C e. 65 C 12. Which of the two liquids has the smaller enthalpy of vaporization, H vap? a. acetone b. 2-propanol c. it is impossible to tell 13. Which of the following complex ions could exist as cis-trans isomers? More than one answer may be correct. a. [Pt(OH) 2 Cl 2 ] 2- (square planar) b. [Co(H 2 O) 3 Cl 3 ] - (octahedral) c. [Fe(CN) 4 (NO 2 ) 2 ] 3- (octahedral) 14. Consider the coordination compound tetraamminedichloromanganese(iv) bromide. Which of the following statements is/are true concerning this compound? More than one choice may be correct. a. The coordination number of manganese is six. b. The oxidation state of manganese is +6. c. This compound is a structural isomer of tetraamminedibromomanganese(iv) chloride. 15. The complex ion [Pt(NH 3 ) 3 Cl] + is square planar. How many unpaired electrons does it contain? a. 0 b. 1 c. 2 d. 3 e. >3 Chem 12 Test 4B page 3 of 6
Problems and Questions Each of the following is worth the indicated number of points, for a total of 55 points. Please show work with units to receive credit. Also, be sure to provide all of the information requested for each question. 16. 6 points Provide a systematic name that corresponds to the formula and a name that corresponds to the compound represented by the formula. a. Potassium tetracyanocuprate(ii) b. [Co(NH 3 ) 4 (H 2 O)Br]Br 2 17. 6 points The complex ion [Mn(NH 3 ) 6 ] 3+ is paramagnetic with a spin equal to two unpaired electrons. Draw an orbital diagram that includes the name of the hybrid orbitals used by the metal atom in bonding to the ligands and the distribution of the electons in the orbitals. 18. 11 points The density of 2.41 m aqueous Mg(NO 3 ) 2 (FW = 148.3 g/mole) is 1.108 g/ml. Calculate the following for this solution. a. The percent by mass of Mg(NO 3 ) 2 in the solution. b. The molarity of Mg(NO 3 ) 2 in the solution. c. The mole fraction of Mg(NO 3 ) 2 in the solution. 19. 8 points A solid organic compound contains carbon, hydrogen and oxygen. A solution of 0.650 g of this compound in 27.80 g of biphenyl melts at 68.54 C. The normal melting point of biphenyl is 70.10 C and its freezing point constant, K f, is 8.00 C/m. What is the molecular weight of the compound to the appropriate number of significant figures? 20. 12 points Suppose that 210. KJ of heat is applied to 18.0 g of liquid mercury that is initially at -25.0 C. In what phase (solid, liquid, or gas) and at what temperature will it end up? Data for mercury: bp = +356.73 C, mp= -38.87 C, H fus = 2.33 kj/mole, H vap = 61.38 kj/mole; specific heats of solid, liquid, and gas are 24.3, 28.0, and 19.66, respectively, all with units of j/g C. 21. 6 points In 0.010 M NaCl the van t Hoff factor, i, has a value of 1.94. How does this differ from the theoretical value of i? Explain what causes it to be different than the theoretical value. 22. 6 points Bromine, Br 2, has a normal melting point of -7.2 C and a normal boiling point of 59 C. Its triple point is at -7.3 C and 40 torr and its critical point is at 320 C at 100 atm. Note that the medley of pressure units is not an error. Use this information to determine whether each of the following statements is true or false. Hint you may want to start by making a phase diagram. TRUE FALSE Bromine will sublime at a pressure of 125 torr. TRUE FALSE Bromine cannot be liquefied at 350 C, no matter how much pressure is applied. TRUE FALSE The melting point of bromine increases slightly with increasing pressure. Temperature --> Chem 12 Test 4B page 4 of 6
TEST #4 Fall 2005 Equation and Information Sheet Conversions K = C + 273 1.00 atm = 760. Torr = 760 mm Hg R = 8.31 joule/mole K (thermo) R = 0.0821 L atm/mole K R = 62.4 L torr/ mole K Vapor Pressure " # ln P2 P1 % " ' & = (Hvap T 2 ) T % " 1 R # T ' where T 2 ) T % " 1 2T1 & # T 2T ' 1 & = # 1 T1 ) 1 % T ' and R = 8.31 Joule / molek 2 & Colligative Properties Electrolyte Solute P soln = P solvent X solvent P vap = P solvent X solute T f = k f m T b = k b m π = MRT (R= as for PV=nRT) Non-Electrolyte Solute T f = i k f m T b = i k b m π = imrt (R= as for PV=nRT) P vap = i P solvent X solute Specific Heat Formula: q= mass x T x sp.ht Chem 12 Test 4B page 5 of 6