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1. Experiment 3.7Solvent and Polarity Effects in Thin-layer Chromatography
2. Purpose of Experiment Determine factors that affect rate of elution (Rf) of organic compounds.
Relationship between polarities of compounds and their rates of elution (Rf)
Relationship between solvent polarity and rate of elution (Rf)
Select an appropriate solvent system to separate and identify components of a mixture.
3. Purpose of Experiment Possible components of unknown mixture
4. Chromatography “Color Writing”
6. Thin Layer Chromatography
7. Thin Layer Chromatography
8. 400mL beaker.
Place a piece of filter paper against side of beaker.
Pour 10mL of developing solvent (mobile phase) onto filter paper.
Cover beaker with a watch glass and allow to stand undisturbed.
9. 2. Apply Samples (spot the plate)
10. 3. Develop TLC Plate
11. 4. Visualize Results
12. 5. Interpret Results (Rf Values)
13. 5. Interpret Results (identify components) Compare Rf values of components in sample to Rf values of standards.
14. Prelab Preparation Read Technique K (pp. 92-100)
Read Experiment 3.7 A & B (pp. 210 – 216)
Title, purpose, procedural reference, procedural changes
Table of reagents:
Structures and hazards of solvents (hexane, ethyl acetate and acetone) and compounds to be separated
Rank the solvents in order of increasing polarity.
Rank the compounds in order of increasing polarity.
Prepare a data table like Table 3.7-1 to record distances and Rf data.
15. Procedural Changes Ethanol will not be evaluated as a solvent.
Do part A in groups of 3.
Do part B individually.
16. In Lab Part A
Determine Rf of trans-stilbene, 9-fluorenone and benzoic acid in hexane, ethyl acetate and acetone.
Each person in group does 1 solvent.
Determine the best solvent to use to separate a mixture of trans-stilbene, 9-fluorenone and benzoic acid.
Review with lab instructor before doing part B.
17. Data Collection Part A
Record the solvent used for each TLC plate.
Measure and record the distances that each compound and the solvent front traveled for each solvent used.
Calculate and record the Rf values for each compound in each solvent.
18. In Lab Part B
Use the best solvent determined in part A to detemine components in an unknown mixture.
19. Data Collection Part B
Record the unknown number.
Record the solvent used for the analysis of the unknown.
Measure and record the distances that each known compound, each spot in the unknown and the solvent front traveled.
Calculate and record the Rf for each known compound and each spot in the unknown.
Identify components in unknown.
20. Thin Layer Chromatography TLC lab technique hints
Slide watch glass off beaker instead of lifting it off to maintain solvent vapor saturation in beaker.
Keep spots small.
Never double dip spotting pipette.
Put sample(s) to be analyzed near center of plate.
Separate spotting points evenly.
Do not disturb beaker during development.
21. Thin Layer Chromatography How does solvent polarity affect Rf?
How does solvent polarity affect relative Rf of 2 or more components?
How does component polarity affect Rf?