Student Comments 2007: Extraction of Caffeine from Tea
In the first part of the experiment when you perform the extraction, you might not get two distinctly clear layers. There might be some bubbles that form in the bottom layer. In this case, simply take a stirring rod and GENTLY stir up those bubbles so that your bottom layer will form more clearly. Then drain the bottom layer to get a nice clear liquid! MW
For the extraction part of the experiment, the lab handout simply statesto pour in 20 mL of dichloromethane.Istarted with the dichloromethane and then added the tea mixture. I got arather nice separation of the layers. A few of my labmatesstarted with the tea mixture and then added the dichloromethane. For some reason, their layers took somewhat longer to separate. So, I recommend startingwith dichloromethane and then add the tea mixture.
When you get to the extension of experiment 8, if you choose an energy drink, use more then 20mL of dichloromethane during the liquid/liquid extraction. This will allow for a slightly larger sample of caffeineon which to perform lab tests.AK
In this lab do not shake your funnel that hard because it will take long for the two layers to separate. KM
Due to the fact that the tea contains tannins, it may be difficult to extract the solution three times with 20 ml's of CH2Cl2 (dichloromethane). In my case my tea mixture had too many tanninsand it would not separate in the sep funnel once the dichloromethane was added. I suggest to keep adding the dichloromethane until there is a separation. ( I had to add 40 ml until it finally separated!) EP
After completing the extraction you are to weight the crude caffeine that you obtain. My weight actually went down. After letting the beaker cool the weight still remained lower than it should have been. This happened to several students. Be aware you might need to "fudge" some data. EC
When you sublimate the product, keep your sublimated product covered at all times when it is under the hood. The vacuum will suck up the product because it is so light. Move the product outside of the hood before recovering it. SP
When extracting the caffeine from the tea bags, the instructions say to squeeze the tea bags to liberate the rest of the water. Do not use any of the objects in the drawer that have sharp edges. Try to just uses your stirrer (or the flat end of the spatula). After boiling, the tea bags are very easy to rip open accidentally if you aren't careful while squeezing. PH
when squeezing your tea bags i recommend you to be gentle with the bags because as i was squeezing themsome of the bagscracked openallowing impurities to go into your solution. this also calls for soluble the work because then you must vacuum filter the solution several times before getting most of the impurities out of the solution. PL
Dichloromethane really is a very harsh chemical. Accidentally spilling some even on your gloves will cause the skin to burn. Proceed to wash the skin with cold water until the burning stops. Be careful because you are using large amounts of it in this lab so remember to wear gloves and goggles and try not to spill any! EP
Don't waste your time untangling tea bags. It is not necessary.Your time is better spent boiling the tea bags. Don't forget to save the combined runoff of extraction, this will be your future caffeine sample.KS