midterm problems 3

midterm problems 3 - chromatography? a) mobile phase b)...

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Lecture 3 Practice Problems 1. Which of the following does not affect the polarity of a compound? a) electronegative atoms b) solubility c) hydrogen bonding d) polarizability 2. Give the order of elution of the following compounds from a column of SiO 2 using a solvent system consisting of 1:1 Ethyl Acetate:Hexanes. NH 2 O O O ONa OH O 1 2 3 4 5 6 a) compound 6, then 3, 5, 1, 4, and 2. b) compound 5, then 1, 2, 4, 3, and 6 c) compound 3, then 6, 4, 1, 5, and 2 d) compound 6, then 5, 2, 4, 3, and 1 3. How would the order of elution change from question 2 if a C-18 column was used? a) the non polar compounds will elute first b) the polar compounds will elute first c) the order of elution will not change d) Both B and C 4. Which of the following terms best describes the use of silica gel in column
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Unformatted text preview: chromatography? a) mobile phase b) eluent c) load band d) stationary phase 5. Calculate the R f for the most polar compound on the following TLC plate: ( Note: All measurements lists are given in mm ) a) .38 b) .64 c) .93 d) .59 6. A student isolates a compound from a normal phase column. To ensure that the compound is pure, the student runs a TLC (also normal phase) and the spot has a very low R f . What should the student do to increase the R f value in order to establish purity of the compound? a) spot more of the sample onto the TLC plate b) increase the time which the TLC plate is developed c) increase polarity of the mobile phase d) decrease polarity of the mobile phase 7. A mixture of 2 compounds is injected onto an HPLC column. The first compound eluted after 2.7 minutes and had a peak width of 4.2 minutes. The second compound eluted after 6.4 minutes and had a peak width of 2.6 minutes. Calculate the value for Resolution. a) 1.7 b) 1.1 c) .66 d) .89 72 67 46 27 2...
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midterm problems 3 - chromatography? a) mobile phase b)...

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