Name ID # For relatively dilute aqueous solutions the molality and molarity are approximately equal.

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1 Name ID # 1 CHEMISTRY 212, Lect. Sect. 002 Dr. G. L. Roberts Exam #1/Sprng 2000 Thursday, February 24, 2000 CLOSED BOOK EXM No notes or books allowed. Calculators may be used. tomc masses of nterest are ncluded on the last page. Perodc tables are not allowed for ths exam. CIRCLE LL OF YOUR NSWERS TO THE PROBLEMS BELOW. For problems that do not nvolve multple choces wrte your fnal answer n the answer box. SHOW LL WORK FOR CREDIT on non-multple choce problems. nswers gven wth no work shown wll receve zero credt. (3 ponts each) 1. Most gases become less soluble n water as the temperature ncreases. What can be concluded about the sgns of Hsoln and Ssoln n ths case? Hsoln<0 and Ssoln<0 Hsoln<0 and Ssoln>0 Hsoln>0 and Ssoln<0 Hsoln>0 and Ssoln>0 2. soluton s prepared by dssolvng g sulfurc acd, H2SO4, n enough water to make ml of soluton. If the densty of the soluton s g/ml, what s the molalty? m m m m 3. The solublty of gaseous solutes n lqud solvents s greater when the external pressure over the soluton s ncreased external pressure s decreased partal pressure of the gas above the soluton s ncreased partal pressure of the solvent s ncreased 4. ll of the followng factors affect reacton rates: concentraton of reactants, concentraton of catalyst, reacton temperature, surface area of a sold reactant or catalyst. 5. Collgatve propertes depend on the concentraton of solvent molecules or ons n soluton but not on the chemcal dentty of the solute. 6. For relatvely dlute aqueous solutons the molalty and molarty are approxmately equal. 7. ccordng to Raoult s Law, the equlbrum vapor pressure of a pure lqud s always decreased when a substance s dssolved n the lqud. 8. The solublty of argon n water at 25 C s M. What s the Henry s Law constant for argon f the partal pressure of argon n ar s atm? x If one mole of each s dssolved n 1.00 lter of water, whch wll lower the vapor pressure the most? C12H22O11 NaNO3 C3H7OH MgCl2 10. ssumng that sea water s a 3.5 wt% soluton of NaCl n water, calculate ts osmotc pressure at 20 C. The densty of a 3.5% NaCl soluton at 20 C s g/ml. 1.0 atm 15 atm 29 atm 100 atm 11. soluton of 62.4g of nsuln n enough water to make 1.00 L of soluton has an osmotc pressure of atm at 25 C. Based on these data, what s the molar mass of nsuln? 621 g/mol 5000 g/mol 7570 g/mol 71,900 g/mol 12. t 80 C, pure lqud has an equlbrum vapor pressure of 700 mmhg and pure lqud B has an equlbrum vapor pressure of 940 mmhg. What s the mole fracton of n the vapor for a X=XB=0.500 soluton?

2 Name ID # Whch statement s true for the general rate law: Rate = k[] m [B] n? It can be wrtten from the stochometry of the overall reacton. The overall order of the reacton s equal to m tmes n. The values for the exponents must be determned by experment. The exponents n the rate law must be postve ntegers. 14. The reacton that takes place n a Breathalyzer for determnng the alcohol level n a person s bloodstream s gven below. If the rate of appearance of Cr2(SO4)3 s 1.24 mol/mn, what s the rate of dsappearance of C2H6O? 2K2Cr2O7 + 8H2SO4 + 3C2H6O 2Cr2(SO4)3 + 2K2SO4 + 3C2H4O2 + 11H2O mol/mn 1.86 mol/mn mol/mn 3.72 mol/mn 15. For the general rate law, Rate = k[][b] 2, what wll happen to the rate of reacton f the concentraton of s trpled? The rate wll be halved. The rate wll be trpled. The rate wll be doubled. The rate wll reman the same. 16. Whch of the followng statements are true about reacton mechansms? I. rate law can be wrtten from the molecularty of the slowest elementary step. II. The fnal rate law can nclude ntermedates. III. The rate of the reacton s dependent on the fastest step n the mechansm. IV. mechansm can never be proven to be the correct pathway for the reacton. I, II, III II, IV I, III I, IV 17. Whch of the followng statements are true about reacton order? I. plot of ln [] vs. t s lnear for a frst-order process. II. plot of 1/[] vs. log t s lnear for a second-order process. III. plot of log [] vs. t s lnear for a frst-order process. IV. plot of 1/[] vs. t s lnear for a second-order process. I, II, III II, III,IV I, III, IV I, II, IV (e) None of the above 18. ccordng to Collson Theory, a chemcal reacton takes place f the energy of the collson between two molecules s suffcent to break chemcal bonds, thereby provdng a sound explanaton of the role of Ea. 19. Whch of the followng statements does not descrbe the equlbrum state? Equlbrum s dynamc and there s no net converson to reactants and products The concentraton of the reactants s equal to the concentraton of the products. The concentraton of the reactants and products reach a constant level. The rate of the forward reacton s equal to the rate of the reverse reacton. 20. Whch of the followng statements s false regardng the equlbrum constant, Kc? Kc for a reacton at a partcular temperature always has the same value. Kc for the reverse reacton s the negatve of Kc for the forward reacton. The numercal value of Kc depends on the form of the balanced equaton. When quotng Kc t s customary to omt unts. 5pts 21. When g of K3Fe(CN)6 s dssolved n g of water, the freezng pont s found to be C. How many ons are present for each formula unt of K3Fe(CN)6 dssolved? (The value of " may or may not be a whole # nteger). =

3 Name ID # The ntal rate of a reacton + B C was measured for several dfferent startng concentratons of and B, wth the results gven below. Usng these data determne the rate law for the reacton; the magntude of the rate constant; the rate of the reacton when [] = 0.50 M and [B] = M. Run # []/ M [B]/M (rate)0/ (M/s) x x x x 10-4 rate= k= rate= 23. ssumng that the loss of ablty to recall learned materal s a frst-order process wth a half-lfe of 70 days, compute the number of days requred to forget 70 percent of the materal that you have learned n preparaton for ths exam. (ssume constant temperature and no further reference to the learned materal durng the decay perod.) t= 24. compound of cobalt, carbon, and oxygen contans 28.10% oxygen and 34.47% cobalt. When 0.147g of ths compound s dssolved n 6.72g of cyclohexane, the soluton freezes at 5.23 C. What s the molecular formula of the compound? Molecular formula 5pts 25. Wrte the equlbrum equaton for the reverse reacton: 2 CH4(g) + 3 O2(g) 2 CO (g) + 4 H2O (g)

4 Name ID # 4 Potentally useful/useless nformaton. f.p. cyclohexane=6.55 C k f (cyclohexane) = 20.2 C/m k f (H 2 O) = C/m k b (H 2 O) = C/m m e = 9.11 x kg m p = x kg m n = x kg J = N m N = m kg s -2 N 0 =N =6.02 x unts/mol d(hg) = 13.6 g/ml R= L atm/mol K R= J/mol K 1 L atm = 101 J = kj 1 Pa = 1 kg/(m s 2 ) = 1 N/m 2 1 atm = 1.10 x 10 5 Pa g = m/s 2 M = n/v w = -P V U = q + w H rxn = Σ H f (products) - Σ H f (reactants) H rxn = U rxn + P V H = nc p T H = c p T q = ms T n P x = = n P total total ph = log [H + ] ph + poh = K a = [ H ][ [ H] + ] K b = [ HB ][ OH [ B] K a K b = K w + ] ph = pk a + log [ base ] [ acd] P = x P T P T = ΣP P2 log = P 1 Hvap R T T F.C. = (#ve) - (#lpe) - ½ (#se) S = k H P o P = P X o P = P X T b = K b c m T f = k f c m Π = MRT ln [ ] t = kt [ ] 0 log [ ] t = kt/2.303 [ ] 0 B log k 2 = k 1 t 1/2 = 0.693/k k = pfz f = e -Ea/RT r.m.s. = Ea R 3RT M m K c = [ ] c C [ D ] a [ ] [ B] d b Q c = [ ] c C [ ] D a [ ] [ B] d b T T 1 2 K p = K c (RT) n K w = [H + ][OH ] = 1.0 x at 25 C

5 Name ID # 5