CHEM 177 Hour Exam II October 1, 2012

Transcription

1 Prof. Thomas Greenbowe Prof. Gordon Miller Dr. Cristina Bonaccorsi This exam consists of 2 parts on 8 pages Parts Page 3 Page 4 Page 5 Page 6 Page 7 SUBTOTAL Grand Total Grading Points 15 pts 21 pts 26 pts 26 pts 12 pts 64 pts 100 pts Score on scantron sheet CHEM 177 Hour Exam II October 1, 2012 Name Recitation TA Recitation Section TA Name Sections Time Berry 14, 38 10, 2 Bobbitt 36, 48 2, 3 Boschen 3, 9 8, 9 Burgin 53, 58 4, 5 Carraher 6, 12 9, 10 Castle 40, 46 2, 3 Chaudhary 47 3 Cole De Silva 21, 31 11, 1 Flood 54 5 Friedrichsen 7, 30 9, 1 Ganesh 5, 11 8, 9 Geraskin 20, 26 11, 12 Geraskina 17, 23 10, 11 Hochstein 35, 42 1, 2 Joshi 16, 29 10, 12 Keller 1 8 Khan 22, 49 11, 4 Kumar 28, 34 12, 1 Kwolek 4, 10 8, 9 Lei 44, 52 3, 4 Lesoine 15, 57 10, 5 Nelson 33, 41 1, 2 Nguyen Peeraphatdit 32, 39, 45 1, 2, 3 Thooft 43, 51 3, 4 Vangaveti 18, 27 11, 12 Wang 50, 55 4, 5 Wanninayake 2, 8 8, 9 Weerasekara 13, 25 10, 12 Xu 37, 56 2, 5 NOTE: To receive full credit for problems on pages 5-7: #13-16, you must clearly show all work and your method of determining the answer must be clear. The final answer must be reported to the correct number of significant figures and have the correct units. Questions are written on both sides of each page. The last page contains useful information and a periodic table; the last page may be removed and used for scratch paper and as a reference. Do not put answers on the tear away page.

2 Please read the following instructions carefully before proceeding! Part I of your exam will be computer graded. In order for the computer to identify who you are, it is important that you complete the information section properly. 2. Write the middle nine digits of your ISU identification number in the boxes A-I. Do not skip any spaces. Below each number, darken the circle that matches this number. For example, See the sample at bottom right. 3. Write your recitation section number in the special code area, boxes K-L, as two digits. Do not skip any spaces. For example, if you are in section 8, write 08. Again, darken the circle that matches the number above it. See the sample at bottom far right m In Part I, select the one best answer for each question. Place your answer on the computer answer sheet by darkening the proper circle for that question. Your computer scan sheet will be your official answer sheet for Part I. he All material (exam, answer sheet, scratch paper) must be returned to your TA in order for us to grade your exam. C e To help you code the correct circles, first write your last name, first name, and middle initial in the boxes (skip a space between each). Then darken the circles that match the letters in the box above it. See the sample to the right. Pr ac tic 1. Ex am You must use a #2 pencil and completely fill in the appropriate circles on the BLUE computer scan sheet.

3 3 Part I: Multiple Choice (12 questions at 3 pts each = 36 points). The answer you fill in on your bubble sheet is the one that will count. You should circle the answer on this sheet for your own reference. There is only one best answer for each question. 1. The reaction Na 3 PO 4 (aq) + 3 HNO 3 (aq) H 3 PO 4 (aq) + 3 NaNO 3 (aq) is best classified as a(n) a) acid-base reaction b) oxidation-reduction reaction c) precipitation reaction d) combustion reaction 2. Assume that an aqueous solution of a cation, represented by shaded spheres, is allowed to mix with a solution of an anion, represented by unshaded spheres. Three possible outcomes are represented by boxes (a) (c). cation anion (a) (b) (c) Which outcome corresponds to the combination of calcium and carbonate ions: Ca 2+ (aq) + CO 3 2 (aq)? a) box (a) b) box (b) c) box (c) d) none of these 3. Acetic acid (CH 3 CO 2 H), formic acid (HCO 2 H), hydrofluoric acid (HF), ammonia (NH 3 ), and methylamine (CH 3 NH 2 ) are commonly classified as a) acids b) nonelectrolytes c) strong electrolytes d) weak electrolytes 4. How many milliliters of a 3.45 M lead nitrate solution are needed to make ml of M solution of lead nitrate? a) 129 ml b) 109 ml c) 101 ml d) 56 ml 5. What is the molarity of an aqueous solution containing 75.3 g of glucose in 35.5 ml of solution? (glucose, C 6 H 12 O 6, F.W. = g/mol) a) 1.85 M b) 2.12 M c) M d) 11.8 M

4 4 6. Solid aluminum and gaseous oxygen react in a combination reaction to produce aluminum oxide: 4 Al (s) + 3 O 2 (g) 2 Al 2 O 3 (s) In a particular experiment, the reaction of 2.5 g of Al with an excess of O 2 produced 3.5 g of Al 2 O 3. What is the % yield of the reaction? (FW of Al 2 O 3 is g/mol.) a) 74% b) 37% c) 47% d) 66% 7. How many grams of sodium chloride are there in ml of a 1.90 M aqueous solution of sodium chloride? a) 1.05 g b) 30.5 g c) 61.1 g d) 122 g 8. The value of E for a system that performs 13.0 kj of work on its surroundings and loses 9.0 kj of heat is kj. a) 22 b) 13 c) 4 d) +4 e) A chemical reaction that absorbs heat from the surroundings is said to be and has a enthalpy change, H, at constant pressure. a) endothermic, positive c) exothermic, positive b) endothermic, negative d) exothermic, negative 10. The heat exchanged during the solution process when solid sodium hydroxide dissolves in water is kj/mol. When a 10.1 g sample of NaOH dissolves in g of water in a calorimeter, the temperature increases from 23.0 C to C. Assume that the solution has the same specific heat as liquid water, 4.18 J/g K. (FW of NaOH is 40.0 g/mol.; assume heat change of the calorimeter to be negligible.) a) 24.0 b) 33.3 c) 33.7 d) 35.2 e) Which of the following conditions would always result in a decrease in the internal energy of a system? a) The system loses heat and does work on the surroundings. b) The system gains heat and does work on the surroundings. c) The system loses heat and has work on it by the surroundings. d) The system gains heat and has work done on it by on the surroundings. 12. A 10.0 g sample of silver is heated to C and then added to 20.0 g of water at 23.0 C in an insulated calorimeter. At thermal equilibrium the temperature of the system was measured at 25.0 C. Assume the specific heat for water is 4.18 J/g C. What is the specific heat of silver? a) 0.11 J/g C b) 0.22 J/g C c) 17 J/g C d) 34 J/g C

5 5 Part II: Problems (64 points total). Show all work to receive credit. Place your answers in the answer spaces. 13. (14 pts) Complete and balance each of the following reactions using neutral species. Write NR for no observable reaction. Identify any spectator ions in the solution and write net ionic reactions. Use the solubility rules to indicate, when appropriate, (aq) (s), (g), or (l). (a) (NH 4 ) 2 S(aq) + Ba(NO 3 ) 2 (aq) Spectator Ions: Net Ionic Equation: What is the name of (NH 4 ) 2 S(aq)? (b) Pb(NO 3 ) 2 (aq) + Na 2 SO 4 (aq) Spectator Ions: Net Ionic Equation: What is the name of Na 2 SO 4 (aq)? 14. (12 pts) In the following reactions, identify the elements or species undergoing oxidation and reduction. Identify the oxidation states of these elements in the reactant(s) and in the product(s). (a) 4 NH 3 (g) + 5 O 2 (g) 4 NO(g) + 6 H 2 O(g) Oxidation: Reduction: Element / Species Oxidation State in Reactants(s) Oxidation State in Product(s) (b) PbS(s) + 4 H 2 O 2 (aq) PbSO 4 (s) + 4 H 2 O(l) Element / Species Oxidation State in Reactants(s) Oxidation State in Product(s) Oxidation: Reduction: Total Pts

6 6 15. (26 points; in five parts on this page) When 75.0 ml of M Na 2 CO 3 (aq) and 25.0 ml of M AgNO 3 (aq) solutions are mixed together in a calorimeter, a white precipitate forms (see balanced equation below). The initial temperature of both solutions is 25.0 C. The final volume is ml. (a) (2 pts) Fill in the phases, i.e., (s), (l), (g), (aq), for the products in the spaces provided below: Na 2 CO 3 (aq) + 2 AgNO 3 (aq) Ag 2 CO NaNO 3 (b) (4 pts) What is the net ionic equation for the reaction that occurs? (c) (8 pts) What is the limiting reagent in this reaction? (d) (8 pts) What is the theoretical yield in grams for the precipitate formed? Ans. Ans. Ans. (e) (4 pts) Given that the enthalpy change for the reaction is exothermic, will the temperature of the solution increase or decrease as the reaction occurs? Briefly explain. Total Pts

7 7 16. (12 points; in three parts on this page) An unknown monoprotic acid, HA(aq), is titrated with a standard solution of sodium hydroxide. (a) (6 pts) Calculate the concentration (in molarity) of the acid solution if ml of the M NaOH solution are needed to neutralize ml of the acid solution. Ans. (b) (2 pts) The acid solution titrated above (25.00 ml) contains g of HA. What is the identity of the acid? Circle your choice below. a) HCl (FW = 36.6 g/mol) b) HBr (FW = 80.9 g/mol) c) HI (FW = 128 g/mol) (c) (4 pts) The acid solution titrated above was obtained from a stock solution of the acid. Calculate the concentration (in molarity) of the stock acid solution knowing that a mL aliquot of the stock acid solution was used to make the mL solution used in the titration. (If you do not have an answer to part (a), use M as the concentration of the unknown acid in ml.) Ans. Total Pts

8 8 INFORMATION 1 mole = molecules E system = E surroundings 1 L = 1000 ml = 1000 cm 3 E = q + w q = mc s T ΔH = q p 1 kj = 1000 J q reaction + q solution = 0 1 K = 1 C Rule for Oxidation States of Elements in Compounds (1) 0 in elements (5) Oxygen: 2, except for peroxides (O 2 2 : 1) (2) Alkali metals: +1 (6) Halogens (Cl, Br, I): 1, except when combined with F or O (3) Alkaline-earth metals: +2 (7) Hydrogen: +1 with nonmetals; 1 with metals (4) Fluorine: 1 (8) Sum of oxidation states in molecule/ion = total charge Solubility Rules: Soluble Compounds contain except Alkali metals (Li +, Na +, K +, Rb +, Cs + + ) and NH 4 - Nitrate (NO 3 ), acetate (C 2 H 3 O 2 ), and bicarbonate - (HCO 3 ) ions Halides (Cl, Br, I ) ions Halides of Ag +, Hg 2+ 2, Pb 2+ Sulfate (SO 2 4 ) ions Sulfates of Ag +, Ca 2+, Sr 2+, Ba 2+, Pb 2+ Insoluble compounds contain except Carbonate (CO 2 3 ), phosphate (PO 3 4 ), sulfide (S 2 ) ions + those with alkali metal ions or NH 4 Hydroxide (OH ) ions those with alkali metal ions or NH + 4 or Ba 2+ 1A 1 1 H Li Na K Rb Cs Fr (223) 2A 2 4 Be Mg Ca Sr Ba Ra 226 3B 3 21 Sc Y La Ac 227 Periodic Table of the Elements Lanthanides 4B 4 22 Ti Zr Hf Rf (261) Actinides 5B 5 23 V Nb Ta Ha (262) 58 Ce Th 232 6B 6 24 Cr Mo W Unh (263) 59 Pr Pa 231 7B 7 25 Mn Tc (98) 75 Re Uns (262) 60 Nd U Fe Ru Os Uno (265) 61 Pm (145) 93 Np (237) 8B 9 27 Co Rh Ir Une (266) 62 Sm Pu (244) Ni Pd Pt Eu Am (243) 1B Cu Ag Au Gd Cm (247) 2B Zn Cd Hg Tb Bk (247) 3A 13 5 B Al Ga In Tl Dy Cf (251) 4A 14 6 C Si Ge Sn Pb Ho Es (252) 5A 15 7 N P As Sb Bi Er Fm (257) 6A 16 8 O S Se Te Po (209) 69 Tm Md (258) 7A 17 9 F Cl Br I At (210) 70 Yb No (259) 8A 18 2 He Ne Ar Kr Xe Rn (222) 71 Lu Lr (260)