Pre Lab Experiment 5: TLC Flashcards
What is TLC and what is it used for?
Thin Layer Chromatography is a technique for rapid separation and qualitative analysis of small amounts of material via solid-liquid partitioning
Generally, what are the materials needed in a TLC?
1) Stationary phase (silica gel plate, more polar)
- Plastic backing on plate
2) Mobile phase (developing solvent, less polar)
3) Sample
4) Developing chamber
What is the equation for Rf?
Rf = distance traveled by solute/distance traveled by solvent = X/Y
What are 2 major reasons for TLC?
1) Establish if two compounds are identical
2) Determine the number of compounds in a mixture
Why must we spot the samples on the same plate for comparison?
Rf is hard to duplicate
What do we use to dissolve benzoin and cinnamic acid?
Use 4-5 drops of ethyl acetate
What step do we use the fume hood?
We use the fumehood to transfer and remove the harmful fumes and gases created in the lab to out of the lab. We use the fume hood when we add our solvent to the chamber.
Why do we add acetic acid to the developing chamber?
It is used when any material is very polar. The acetic acid will increase the polarity of the developing solvent and therefor reduce the amount of attraction the polar compounds usually have for the stationary phase
Why is petroleum ether and ethyl acetate used as a developing solvent?
Because the solvent must be volatile so that when it evaporates, the compound being spotted can be adsorbed onto the solid phase. Petroleum ether and ethyl acetate have very low B.P. so they will be perfect.
Based on the TLC results which is more polar Benzoin or cinnamic acid?
The cinnamic acid traveled a lesser distance so it means it is more polar than benzoin since more polar compounds are attracted more to the stationary phase (silica gel plate).
