labquizkey2

labquizkey2 - KEY Chem 322aL Summer 2003 June 12, 2003 NAME...

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Unformatted text preview: KEY Chem 322aL Summer 2003 June 12, 2003 NAME LAB QUIZ #2 (Five pages — 33 points) lag 277 1. (4) Circle the correct word or phrase in each set separated by / to make the following statement true; note the phase diagram sketched on the board. As a solid sample is progressively purified from C1 to C2 to C3, its melting point increase / decreases a little / a lot , while the range over which solid and liquid are both visible increases decreases a little / 2. (3) A certain sample, X, of "mp" = 88° — 95°, is believed to be e80% cpd P or e80% cpd Q, but might contain neither P nor Q. Pure authentic P melts 100° — 101°; 95% pure authentic com- pound Q melts 97° - 99°. A mixture of X and P has mp = 96° - 98°; a mixture of X and Q melts 82° — 83°. Give the most likely interpretation of these data with regard to the compo- sition of X; state your reasoning concisely. 7L, {ha/{1 )9” I‘M/(7le -2- 3. (5) A certain solid sample comprises 7.0 g A and 10.0 g B. Their solubilities in a solvent S are independent. Each dissolves to the extent of 10 g/100 g S when hot. In cold S, A's solu— bility is 1.0 g per 100 g S; B‘s solubility is 5.0 g/100 g S. (a) (3) Calculate the minimum amount of solvent from which one should recrystallize the sample to obtain pure A. Remember that one should use enough solvent to disgglyeithe_mhol§_§§m2l§ hot and to keep all the impurity dissolved in the cold solution. 71) M “La/c {amp/e, M (0’%o =— M0? 77; “,4 6 W 400/ M 19%?“3/woa S 3 M0 5‘ (b) (2) Calculate the amount of A which precipitates without precipi— tation 9: any 3 from the cold soluiion of (a) above. 300 f M/ WSAMUJJ 17,614“; (J/Mfi J M“ C’lk/(I $34 4. (2) A sample dissolves completely in a hot recrystallizing solvent to give a colorless solution. What should be one next? (one phrase) Coé/ y‘QCYZ/f E’W‘W, (yo Nd?» M chcdq/(dt A071 5. (3) According to the movie "The Wizard of Oz", Wicked Witch of the West (WWW) is very soluble in water. Even at 15°C, one gallon (8 pounds) of water will just dissolve an 80—pound WWW. Recalling WWW‘s last words as she dissolves ("I'm melting, I'm meltingl"), restate the facts of the second sentence without referring to solubility. Include a fraction of water added to WWW and a temperature in your answer (one sentence, <15 wds). Mad /0vf% maria fl fact/w W “P h N" _L Wing 6. (8) Recall the preparation of n—BuI: acetone n—BuBr + NaI —————————9—- n uI NaBépé ‘ MW = 137 FW = 150 UAW Q = 1.27 (a)(4) Suppose one wishes to get at least 36 mmol n—BuI and is confi— dent of getting at least a 60% yield. With n-BuBr limiting, calculate how many mL's of it one should use to assure this result. You may leave your answer factored. ~€ou€r : ('9. 035 NR 4674:“ mo(lfl A M fl‘émoz‘z 4'— “a W (b)(4) The prep was done in acetone solution, but Bond Dissociation Energies of the pure components were used to calculate A6 for the reaction as done. Beside regarding [35's s: (Lfi's a [fiE's, tell what this calculation requires one to know or assume about: (1) the zxgqs of solution of the components, and (2) the mechanism of the reaction. (2) WWWMM 4 CW (A; a (Me (PM “m r m‘r‘é’a N0 Whip % ,ociMJ 7. (4) Note the data below: (1) (2) (3) (5) (6) W4 Reaction Ag (kcal) n—Bu—Br ---—> n—Bu+ + Br' + 178 NaI —-——> Na+ + 1‘ + 164 Q—Bu+ + I' ----> n-Bu—I — 171 Na+ + Br" ---—> NaBr - 174.5 NaCl -—-—> Na+ + Cl’ + 183 neBu—Cl —-——> Q—Bu+ + C1' + 185 Calculate [36 for the reactions n—Bu—X + Na+ ---—> Q—Bu+ + NaX for X = Br and for X = Cl. Given that the overall reaction turning n—Bu—X into n—Bu—I is much faster for X = Br than for X = Cl, tell whether it is possible that the reaction in the first sentence is the slow step for (both) the overall reactions. Explain in <25 words. 8. (2) Note the data below. l|m_n|l fl Z: in the left cgéimn means " mix— ture of CaClZ‘m H20 and CaClZ'n H2O in equilibrium". CaCl2 hydrate mixture 0-1 1—2 2—4 4 6 6 satd aq soln Relative humidity (rh), % 1.25 4.2 14 21 30 The solubility of W(ater) in a certain 0(rganic) S(olvent) is After treatment with CaClZ, the solid has average 3.00 g/L. composition CaC12-4.8W. 9. (2) Calculate the final W conc in the OS. {o/CJ M’XM¢ “(u—.VL‘6‘ :12 V14; :3 LOW” Anhydrous K2CO3 has a capacity of 0.20 gW/gDA. J. L! Calculate how 3.003/1/ K 1H ’ much is needed to dry 800 mL water—saturated OS of ques 8 above; assume all the water is absorbed. ...
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This note was uploaded on 10/21/2008 for the course CHEM 322AL taught by Professor Jung during the Fall '07 term at USC.

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labquizkey2 - KEY Chem 322aL Summer 2003 June 12, 2003 NAME...

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