Fall2007lfl.review

Fall2007lfl.review - Chemistry 201/251 Lab Exam from Dec 1,...

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1 Chemistry 201/251 Lab Exam from Dec 1, 2006 1. In the reaction between sodium benzoate and hydrochloric acid, a precipitate is formed in a good quantity when the mixture containing the sodium benzoate is acidified to pH 2. Why? (A) pH 2 cools the solution and hence results in the formation of more precipitate (B) pH 2 converts the sodium benzoate to benzoic acid which is poorly soluble in water (C) pH 2 produces hydrogen ions that react with benzoic acid making it poorly soluble in water (D) none of the above 2. Which of the following components of Panacetin were soluble in diethyl ether (or dichloromethane)? (A) sucrose and aspirin (B) sucrose and phenacetin (C) phenacetin and aspirin (D) none of the above 3. Which sample shows the highest purity based on melting point results? (A) 130-145 C (B) 110-113 C (C) 70-80 C (D) 160-200 C 4. 5.0 mmols of methyl salicylate (MW = 152.1 g/mole, d = 1.174 g/mL) are needed to react with an excess of NaOH to yield sodium salicylate. How many milliliters of methyl salicylate do you need to start with? (A) 0.64 (B) 1.0 (C) 0.46 (D) 0.55 5. Why is it important to not boil the water when synthesizing aspirin? (A) it makes reaction go too fast (B) it slows down the reaction (C) it causes aspirin hydrolysis (D) it destroys aromaticity 6. In Exp 9, isolation of lycopene, what should you do if you had poor separation? (A) decrease the polarity of the eluting solvent (B) use a shorter column (C) increase the polarity of the eluting solvent (D) all of the above 7. In Exp 21, dehydration of methylcyclohexanol, why do we distill the alkene product out from the reaction system? (A) to make the reaction go forward (B) to slow down the reaction (C) to make the reaction go backward (D) none of above 8. What indicates a positive test for excess hypochlorite on starch-iodide paper? (A) it turns pink/red (B) it turns white (C) it turns blue-black (D) it dissolves 9. Triethylene glycol is used in the luminol synthesis because of its (A) high freezing point (B) high melting point (C) less expensive cost (D) high boiling point 10. In Exp 1, learning the basic operations, theoretically how much benzoic acid (MW=122.1) will be yielded by using 0.4 g of sodium benzoate (MW=144.1) and an excess of HCl? (A) 0.34 g (B) 0.40 g (C) 0.47 g (D) 1.22 g
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Fall2007lfl.review - Chemistry 201/251 Lab Exam from Dec 1,...

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