Exam 1 Key (Chem 102)

Exam 1 Key (Chem 102) - Note: There are 6‘ pages with 25...

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Unformatted text preview: Note: There are 6‘ pages with 25 questions, equal credit — 1 hour ' More Useful Information: osmotic pressure: H = MRT 760 torr = 1 atmosphere = 760 mm Hg Raoult’s law: PA = XA P31 Henry’s Law : Mg = k Pg Blank scratch paper for calculations etc. will be provided by the proctors. Do not use any papers of your own. 1. If 0.139 mole of water is sealed into a 5.0 L flask and the temperature raised to 80.0 °C, choose the correct statement below. Water has a vapor pressure of 370 mm Hg at 80.0 °C. SK {2) A) The water is entirely in the liquid phase with no gas present. . B) The water is entirely in the gas phase with no liquid present. I 1 l , é L! C The final pressure in the flask is 61.2 mm Hg. @The quantity 0.084 mol is in the gas phase. E) There are more moles of water in the liquid phase than in the gas p . hae. Mo‘Ofij 6&3”: VI 1 lav/KT : é7fl/7 é/o)(f>/é,0f’~>3flk u: a 05W w». a... :0 My WWW 2. A sample of a gas in a cylindrical chamber with a movable piston occupied a volume of 4.626 liters when the pressure was 0.983 atm and the temperature was 27.2 ° C . The pressure was readjusted to 1.388 atm by moving the piston. What was the volume occupied by the sample under the later conditions if the temperature remained constant throughout? A 0.303 liters I”, \II > Pg 0., I . w i ers a 2 I D) 6.35 liters V: L 7 ( I E) 6.49 liters 3. Silver oxide, AggO, when heated strongly decomposes to yield silver and oxygen gas. A 4.262 g sample was heated to decompose it completely. What volume, in ml, should the gas collected occupy at 28.3 ° C and 749.0 torr if it behaves as an ideal gas? @2308m1 HSLLQ: ZZZ 346.2 ml 461.6ml 4‘14 L/LZL: 0.015737%1/‘49 0 C) D) 615.5 ml E) 923.2ml ,N &.00 4167 of} 01/ I. gag/7m) (v) = @«WGYI57) [.JQL) (7/9119 \l: 0.2.3&L 4. A sample of oxygen gas was collected by downward displacement of water in a large gas collection apparatus. The total pressure in the collection vessel was 7 44.2 torr, the temperature was 26.0 ° C , and the vessel contained 522 ml of the collected gas. How many moles of oxygen were collected? At 26.0 ° C , the vapor pressure of water is 25.2 W- p ; 7W: 3%. +2£1Tw j? 90: WNW 0.0201 moles UT L 2, : 0.0215 moles - ‘ a. 6 a] A C)0.0842moles @14/750)@%(0,f11)2 1/) (@0361) K] D) 0151 moles W” E) 0231 moles . A 1ng 5", l l2 / ' - 5. The average speed at which a nitrogen molecule effuses at 30.0 C is 480 meters! per second. The average speed at which a butene molecule (C4H8) effuses at this same temperature should then be NLZl g I: 52 A) 120ms‘1 \f, B) 170ms-1 \I ML _ qgo ~ C; L ms“1 l 2 — ¢/_ m l W0 vb I 4? 679ms‘lL - vi: qg%.%lv = 1W1 M/J’ 6. The van der Waals equation of state for a real gas is: V0 (0 l IL I 0 Z. (P+n2a/V2)(V¥nb)=nRT - In this equation, the van der Waals constant, a, represents a correction for: A) a positive deviation in the value of PV from that for an ideal gas due to the finite volume of space occupied by molecules of a real gas , ' B) a negative deviation in the value of PV from that for an ideal gas due to the finite volume of space occupied by molecules of a real gas C) a positive deviation in the value of PV from that for an ideal gas due to the attrac— tive forces between the molecules of a real gas @a‘ negative deviation in the value of PV from that for an ideal gas due to the at— tractive forces between the molecules of a real. gas E) a positive deviation in the value of PV from that for an ideal gas due to the finite mass of the molecules of a real gas ’ 7. A mixture of 80% 02 and 20%N2 is held at a total pressure of 0.1 atm and a temperature of 50° C . Which statement about the average molecular speeds and the kinetic energies is true ? A) N2 and 02 molecules move at the same average speeds. B) The energy of N2 is greater than that of 02 C) The energy of N2 is less than that of 02 @The speed of N2 is greater than that of 02 E) The speed of N2 is less than that of 02 This is version 0 of the exam 8. If 34.0 g of a solid with a molecular weight of 174.0 g/mole, which is already at its 9 10. 11. 12. a melting point, requires 21.3 kJ of heat to melt it, what is the molar enthalpy of fusion, inkJmol‘l? / a v”, A) 3.60x10-3kJm01-1 (3177/ M —— (9. W5 4701225 1 1:3 k 370in B) 4.16 M mol’lL 2.40 X 10‘1 kJ mol"-lL E), 109 kJ moi-1 1.26 X 105 kJ mol—1 ’1 _ MWXJ/ . A substance has a heat of fusion of 61.5 kJ/mol and a heat of condensation of —167.4 kJ/mol. What is the heat of sublimation in kJ/mol? PM A) —105. B) —61.5 C) 10;): D) 167.4 @2289 g i U ' MWT MQI I”l VlLL v Z 4—[ g 7 IL (3" T C4 Mgr: stiff . v If 5,,H1'M : 147.L/+6/,1’C— LLXflkJ The type(s) of solid(s) that are characterized by low melting point, softness, and low electrical conduction is / are solids. _ molecular lam) ionic HI C) metallic D) covalent-network- E) both ionic and molecular . X—ray diffraction measurements revealed that Cu crystallizes in a face centered cubic lattice in which the unit cell edge length = 361.5 picometers. Calculate the atomic radius of the Cu atoms in this crystal, based on the usual assumption that the atoms are tightly packed in the unit cell. A) 90.4 pm B)¥127.8 pm C) bit/La/JW‘J‘ ram/7953 Eigfi J'WMJ/l/f ': garb/14:127.)? Based on molecular mass and dipole moment of the five compounds in the table below, which should have the highest boiling point? D) 170.4 pm 7—” Llfo'valw; E) 180.8 pm Substance Molecular Mass (amu) Dipole Moment (D) Propane, CHBCHQCHE, 44 0.1 Dimethylether, CH300H3 46 1.3 Methylchloride, CH3Cl 50 1.9 Acetaldehyde, CHgCl-IO 44 2.7 {‘0 .' b .Acetonitrile, .CH30N,.. .41 . 3.9 . . . ‘ l A) CH3CH2CH3 B) 014300143 C) CH301 CH30HO CH3CN \Lt‘fl/ I 13. Ethanol, CgH5OH, melts at —114 °C and boils at 78 °C. The enthalpy of fusion of ethanol is 5.02 kJ/mol and its enthalpy of vaporization is 38.56 kJ/mol. The specific heats of solid and liquid ethanol are 0.97 J/g-K and 2.3 J / g-K, respectively. How much ‘ heat is required to convert 75.0 g of e anol at —-120 °C to vapor at 78 °C? A) 33.627 k] B) 0.0336 id @105 kJ M5 kJ E) 20.66 M : ltéj M2107 flflb All-b3qu 1 Q“ U‘w) 1 ‘57“ if 1:: w my 2 (m) a, (ab 10 J, Q Mg - Q23“: (73;) (787W) 2 33/’ ,_ Al’l “(fl , (O 3 4sz AH-SJQ/vil:@vofl (7J3) -’ J0 Li.) l6 1 14. The critical temperature and pressure of 082 are 279°C and 78 atm, respectively. At temperatures above 279°C, which states from the list below best describe the state of 082 ? A) solid B) liquid C) liquid and gas D _ gas supercritical fluid and gas 15. Which phrase best describes viscosity ? A) the ” skin” on a liquid surface caused by intermolecular attraction the resistance to flow C) the same as density D) inversely proportional to molar mass E) unaffected by temperature Witt? 16. The solubility of Ar in water at 25°C is 1.6 X 10‘3 mol/ L when the pressure of the r 1 above the solution is 1.0 atm. What is the solubility in mol/ L of Ar at a pressure offl 2.5 atm ? M I is P? l? 2 Lt] are/0‘] 'V’l/ajwl M:d.6*m 3X2“ A) 1.6 x 103 B) 6.4 x 10~4 @4.0 x 10-3 D) 7.5 X 110-2 E) 1.6 >< 10-3 2 "/«ij 17.. A solution was prepared by dissolving 15.0 g of NH3 in 250 g of water. The density of the resulting solution is 0.974 g/mL. What is the molarity of NH3 in the solution ? A) 0.00353 B) 0.882 (3)1600 iD)l3.24 E) 3.53 153%17 : 0. KKLMH’Ja NH) 18. WhiCh one of the following substances is most likely to dissolve in 0014 ? CBr4 B) HBr C) H01 D) CHgCHgoH E) NaCl 19. A solution prepared by dissolving 0.60 g of nicotine (a nonelectrolyte) in water to make 12 mL of solution has an osmotic pressure of 7.55 atm at 25 °C. Which is the best estimate of the molecular weight of nicotine ? ' A) 28 B) 43 e) 50 160 E) 0.60 077:7. new 2: M KT 2 M (‘ otofllfmé’kly‘ Hzmflm 20. Which one of the following 0.1 M aqueous solutions would have the lowest freezing point? I L. My); FVOLQ(ILI¢I(DJ‘ A) NaCl A1(N03)3 0) K2CTO4 D) Na2SO4 E) sucrose [bit 21. What is the molarity of an aqueous sodium chloride solution that is 13.0% sodium chloride by mass and that has a density of 1.10 g/mL? A) 143 @245 C) 2.56 D) 2.23 E) 1.43 x ‘10-? (MU: X/fiftl]: W‘Jz— 22. Which phrase best describes the reason that the dissolution of gases in water is Virtually always exothermic ? ' 'O‘n'e of the endothermic steps of“ the t‘hreesstep dissolution” process is“ unnecessary separation of solute particles) B) the exothermic step of the three—step dissolution process is unnecessary C) gases react exothermically with water D) neither of the endothermic steps in the three—step dissolution process is necessary E) all three steps in the three—step dissolution process are exothermic 23. Concerning the phase diagram below, which statement is correct about the substance at the temperature and pressure of point d 7 V A) The substance will sublime. B) There Will be an equilibrium between the solid phase and the gaseous phase. Vaporization and deposition will take place simultaneously. Condensation and evaporation will take place simultaneously. E) The substance will be a superfluid. WWW? 24. At 28.0 ° C , the vapor pressure of acetonitrile, CH3CN, is 102.0 torr while that of acetone, 031—160, is 228.9 torr and for CSg the value is 378,7 torr. A three component solution is made by adding 0.300 moles of CH3CN and 0.400 moles of C3H60 to 0.350 moles of C82. The mixture behaves as an ideal mixture. What is the vapor pressure ofthe solution? ' Tar-hue 11/1/45 : 0.2 +0.‘{ +03 f“; [101’ [Wt/“677 A‘ 203 torr p \ Y r”: (OJ/1,01”) CIOL) : Lqi/L/ Tor-{V g @243 torr alllCVl/T a h _ $772— Mir D) 262 torr pgfibot X W; (Qty/[1%)(LLX’?) P . - l 1 :lLé- WV misfits: came/7m /- T512); Z‘fld 73W 25. Pure cyclohexane, C6H12, has a freezing point of 6.53 ° C . Its freezing point depression constant is: K f = 20.0 ° C m‘1. A solution was made by taking 11.40 g of an unknown non-electrolyte and dissolving it in 150.0 g of cyclohexane. The measured freezing point of the solution was -0.78 ° C . Calculate the molecular weight of the unknown [/0 :gbjjgfe- H ,, are C“? W? “W " e t: M? MM .. WI! B :mol—l /VV\ 2 0, 3 6 “1’qu l (/1'75 C 208 g mol—1 D) 264cgmol—3L ((-qfl/aflw 16$: " E) 1949 g mol—1 ...
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Exam 1 Key (Chem 102) - Note: There are 6‘ pages with 25...

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