Chemistry 29a Summer 2000
Final Exam M. Walker
YOUR NAME __________________________________
Duration 60 minutes. All questions are worth 12 points unless stated.
1. Octane (an alkane) has a lower Rf than 1-octanol (an alcohol) on silica gel.
TRUE or FALSE
2. When 1-chlorobutane is chlorinated using AIBN and SO2Cl2, and the products (after workup) are analyzed by GC (using a column like you used in lab), the product with the shortest retention time is 1,1-dichlorobutane.
This suggests that:
(a) 1,1-Dichlorobutane is the least stable product
(b) 1,1-Dichlorobutane is the product which forms at the slowest rate
(c) 1,1-Dichlorobutane is the product with the lowest boiling point
(d) Both (a) and (c) are true.
3. In the separation of benzoic acid from benzophenone, the alkaline aqueous layer is acidified with HCl, resulting in the formation of a white precipitate. This precipitate consists of the substance:
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4. What would you expect to be a good recrystallization solvent for ditolyl ketone, given the following solubility data:
Cold temperature: Insoluble in water, methanol, hexane, soluble in acetone.
Hot temperature: Insoluble in water, hexane, soluble in methanol, acetone.
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5. An impure sample of benzoic acid is recrystallized from a toluene-cyclohexane solvent pair by heating the benzoic acid and solvent mixture together, then cooling, evaporating off the solvent and weighing the crystals. The melting point of these crystals should be higher than the MP of the starting sample.
TRUE or FALSE
6. Unknown sample X (m.p. 141-142oC) was mixed with three known pure samples A, B, C. The melting point of the mixed samples were as follows:
A&X, 141-142 oC; B&X, 134-137 oC; C&X, 132-136 oC. What is X?
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7. What are possible products from elimination of HBr from 1-methyl-1-bromocyclohexane?
8. 1-Bromobutane was prepared from 1-butanol by reaction with NaBr and H2SO4, with NaHSO4 as a by-product. How was the NaHSO4 separated from the 1-bromobutane?
(a) By distillation
(b) By extraction with H2SO4
(c) By filtration
(d) By washing with aqueous NaOH
9. Sulfuryl chloride was used as a radical initiator in the radical chlorination of 1-chlorobutane.
TRUE or FALSE
10. Draw a basic apparatus setup for fractional distillation (great art not required!):
11. When distilling a mixture of hexane (b.p. 68oC) and methylcyclohexane (b.p. 98 oC), the first five drops of liquid collected were tested on GC. Is it true that the peak area for the first peak is much greater than the peak area for the second peak?
TRUE or FALSE
12. The IR spectrum of a certain material is shown below. Which of the following bonds are present?
(a) O-H and C-H (b) O-H only (c) C=O and C-H (d) C-H only 13. (10 points only) When adding NaHCO3 to benzoic acid in expt. 5, the reaction which occurs can cause a minor hazard. What is this hazard? (a) A highly corrosive solution is formed (b) The solution may catch fire (c) A froth of CO2 gas may be produced (d) The reaction mixture gets extremely hot due to the exothermic reaction The final three questions all relate to the series of related compounds shown:
14. Which compound would you expect to be most soluble in water?
(a) A (b) B (c) C (d) D
15. Which would you expect to have the highest Rf on TLC?
(a) A (b) B (c) C (d) D
16. 9-Fluorenone (B) may be recrystallized from either hexane or methanol. Which would be better to use, if the major impurity is fluorene (A)?
METHANOL or HEXANE