Macroscale and Microscale Organic Experiments
7th Edition
ISBN: 9781305577190
Author: Kenneth L. Williamson, Katherine M. Masters
Publisher: Brooks Cole
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Chapter 8, Problem 10Q
A TLC plate showed two spots with
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The identity and ratio of solvents are necessary in chromatography for achieving a good separation. What would happen if your solvent had an overly polar TLC developer? What would happen if it was overly non-polar?
A standard sample of compound A was placed on a silica TLC plate. After elution in 30/70 ethyl
acetate/hexane, the sample showed a single spot at 3.4 cm (relative to the initial point) after the
solvent had risen to 7.1 cm (relative to the initial point). A sample which was thought to contain
this compound was analyzed by TLC and showed two spots after elution in the same solvent
system. The solvent height for this plate was 6.5 cm (relative to the initial point) and the spots
were located at 3.6 cm and 5.2 cm (relative to the initial point). Can either of these spots possibly
be compound A? Explain.
Include a discussion of the R, for each spot.
How does increasing the polarity of the developing solvent affect the Rf of a compound on a silica gel TLC plate?
Chapter 8 Solutions
Macroscale and Microscale Organic Experiments
Ch. 8 - Prob. 1QCh. 8 - Prob. 2QCh. 8 - What problem will ensue if the level of the...Ch. 8 - Prob. 4QCh. 8 - Prob. 5QCh. 8 - Arrange the following in order of increasing Rf...Ch. 8 - What will be the result of applying too much...Ch. 8 - Prob. 8QCh. 8 - Prob. 9QCh. 8 - A TLC plate showed two spots with Rf values of...
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- Thin Layer Chromatography why the non-polar compounds move up the plate most rapidly (higher Rf value), whereas polar substances travel up the TLC plate slowly or not at all (lower Rf value)? Please help me explain this question! Thank you so much!arrow_forwardHPLC VFA analysis - why do I get so different peaks for very similar samples?arrow_forwardIn TLC, why does a 3:1:1 ratio of the developing solvent of n-butanol/acetic acid/water move up the TLC plate so slowly?arrow_forward
- A student spots an unknown sample on a TLC plate. A single spot with an Rf of 0.55 showed up on the plate after developing the sample in hexanes-ethyl acetate 50:50. Does this prove that the unknown is a pure compound?arrow_forwardThe following data were obtained by gas chromatography for a 30-cm packed column: Compound Retention time (min) Peak width (min) Air Hexane 0.9 3.7 0.70 Cyclohexane 4.5 0.94 Calculate the selectivity factor for hexane and cyclohexane.arrow_forwardA student spots an unknown sample on a TLC plate and develops it in dichloromethane solvent. Only one spot, for which the Rf value is 0.95, is observed. Does this indicate that the unknown material is a pure compound? What can be done to verify the purity of the sample?arrow_forward
- On a paper chromatogram, a spot produced by blue ink traveled 2.7 cm, and the solvent "front" traveled 5.7 cm during the experiment. Calculate rate of retention of flow, Rf, for the blue ink.arrow_forwardMatch column A with Column B. Given: Samples were spotted on the TLC plate and after performing the experiment, the following were obtained: Component A, Rf = 0.2 B, Rf = 0.5 C, Rf = 0.8 Which is the most polar? A. Component A v Which can dissolve in water? B. Component B Which has affinity to the stationary phase? c. Component C Which has affinity to mobile phase? Which is the least polar Which can dissolve in organic compounds? v Which component is slightly hydrophobic and hydrophilic? Activaarrow_forwardA student used thin layer chromatography to confirm whether he could successfully separate two compounds. Here is the TLC plate he obtained after 30 min. Stationary phase was silica gel and mobile phase was 95 % ethyl acetate and 5 % Hexane mixture.arrow_forward
- Consider the following errors that could be made when running TLC. Indicate what should be done to correct the error. a) A two-component mixture containing 1-octene and 1, 4-dimethylbenzene gave only one spot with an Rf value of 0.95. The solvent used was hexane. b) When a TLC plate was developed, the solvent front ran off the top of the plate.arrow_forwardA chemist was able to extract a biologically active compound and wants to purify the sample since he is sure that the sample still contains impurities. After running the extract in TLC, the chemist found out that the sample produced only one spot near the solvent front. Suggest how the chemist can achieve a better resolution for the chromatogram.arrow_forwardGiven that the following chromatogram for the separation of two solutes (A and B) on a 25 cm long HPLC column. The retention time of the un-retained species is 0.9 minute, compound A is 6.0 min and compound B is 7.8 min. The width of the eluting peak at the baseline for compound A is 1.5 min and for compound B is 1.4 min. Based on this chromatogram, answer the following questions: A (6 min) B (7.8 min) 1.01 (i) (ii) Absorbance 0.5- 0 tm (0.9 min) 10 15 20 time (min) Calculate the resolution and selectivity factor achieved for solutes A and B. Calculate the linear velocity of the mobile phase in the columnarrow_forward
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