Question

Chem lab questions for (extracting caffeine from tea bag water using dichloromethane --> filtered --> steamed --> obtain caffeine )

1. Does TLC give a conclusive identification of caffeine ( extracted from tea bags) ? why or why not?

2. Is the extract a pure compound or mixture of compounds? Explain

Answer 1

Answer:

1) No, because the tea extract shows a spot very similar to the spot of pure cafeine but there could be some other compound the could have propreties very similar to caffeine.

2) Mixture.

Explanation:

1) TLC is done by using a crude extract and a pure standard, giving an indication on the presence of the compound in the crude extract based on the Rf and color characteristics (if a derivatisation reagent is used or based on 'quenching' or fluoresence (color) characteristics when viewed under UV light). TLC is not an absolute confirmation tool, it acts like indicative tool that is cheap to run, so if there is no TLC indication of presence one did not wasted solvent using HPLC.

The confirmation is to either isolate the compound from the crude extract or run either HPTLC or HPLC of the extract followed by mass spectral analysis to confirm the compounds presence.

2) Tea is a natural product and nature does not yeld pure compounds (with the exception of noble gases), so it must be a mixture.

Also, the TCL experiment confirms that tea is a mixture indeed.