Caffeine Lab Flashcards
Why would you add sodium carbonate to tea water?
To convert the acids in the tannins into their sodium salts, which are highly soluble in water.
After one has added sodium carbonate to the tea water, will the caffeine be found in a separate later?
No. You have to add methylene chloride. Although caffeine is soluble in water, it is much more soluble in methylene chloride
How can the methylene chloride be removed from (the crude caffeine + methylene chloride solution)?
Evaporation - rotovap
Why must the crude caffeine be purified (sublimated) at reduced pressure?
It must be purified at reduced pressure to prevent decomposition.
Why is it important to push down gently on the tea bag with a test tube when brewing?
In order for all of the tea leaves to be in constant contact with the water.
What is the first thing you add to the brewed tea solution? Why?
.5g Sodium bicarbonate
What is an emulsion?
An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable)
Why did we place the extraction mix in the centrifuge?
The extraction mix was placed in the centrifuge to break break the emulsion during centrifugation
What is indicative of an emulsion in the caffeine mixture>
a green-brown layer between the clear methylene chloride layer and the top aqueous layer
What is the dark layer in the caffeine experiment?
It is the aqueous layer and it sits on top. It contains tannin salts, etc.
(Caffeine experiment) Once you have extracted the methylene chloride layer, what’s the next step?
Add some drying agent.
(Caffeine experiment) Once you have added drying agent to the extracted methylene chloride layer, what are the last steps?
1) evaporate solvent 2) sublime caffeine (in order to separate it from alkaloids)
What would happen if you tried to sublime caffeine at standard pressure?
It would melt.
Caffeine will sublimate at reduced pressure.
Sublimation procedure
1) Assemble apparatus before
putting ice in sublimation tube
2) Heat gently with microburner,working from bottom up
3) ‘Chase’ the solid onto the coldfinger—do not let it ‘escape’ through the vacuum tubing
4) Remove water from cold fingerbefore disassembly of apparatus
5) Carefully turn off vacuum and disconnect tubing
6) Scrape caffeine off cold finger onbench outside the hood
