Experiment 7: Functional Groups & Thin Layer Chromatography Flashcards Preview

Chem1048 Lab Test Prep > Experiment 7: Functional Groups & Thin Layer Chromatography > Flashcards

Flashcards in Experiment 7: Functional Groups & Thin Layer Chromatography Deck (12)
Loading flashcards...

Name three common uses of TLC

1. Used to identify compound and determine homogeneity of the sample
2. Monitor the progress of a reaction and verify the substance’s identity
3. Separate mixtures into its components and tell if it is pure


Never touch the coated surface of the TLC plate with your fingers. Why?

- the oils and amino acids from our skin would go onto the plate and show up as spots and obstruct actual spots giving unreliable results


Why should you not allow the solvent to migrate all the way to the end of the plate

- wouldn’t be able to see the spot
= cannot measure distance travelled by spot
= can’t calculate rf (retention factor)


Why should you avoid pressing too hard while marking the coated surface of the plate?

- silica Gel would peel off plate


What forces the mobile phase to move up the TLC plate?

The capillary action force


Why is it not advisable to use ink to label your TLC plate?

- dye moves up plate as it develops => streaks ruin plate


You are supposed to use the narrow end of the capillary tube to spot your sample on the TLC plate. Why?

- large spots would run into each other = ruin plate
- difficult to differentiate between samples


Why should the beaker be covered during the development of the chromatograph?

So that the solvent moves up the plate instead of evaporated
- so that beaker becomes saturated with solvent vapor


The solvent level in the developing beaker should always be below your TLC spots. Why?

- solvent would dissolve other samples
= results inaccurate


The final chromatograph has fewer spots than expected and the ones that are visible are very faint. Why?

5 small spots were made on 1 area which then blended together to give us a single resultant spot for each sample.
The sample evaporated leaving only a faint mark.
The drops were too small and it was a dilute sample


Your final chromatograph has spots that are dark enough to see, but they are very broad and overlap. Give reasons.

The drops were too large hence the samples mixed together
- the chromatograph was seen to have broad, overlapping spots


There are no bands in the chromatograph, but the Solvent at the bottom of the beaker has a bright colour. What happened?

The sample solution became dissolved into the solvent and it colored the solution.
No bands formed