Extraction of Caffeine from Tea Leaves

Question 1

what is the caffeine found in tea?

Answer 1

a crystalline methyl xanthine and member of alkaloid class

Question 2

What are alkaloids?

Answer 2

nitrogen-containing compounds present in plants

Question 3

What is the purpose of adding a mild base to the tea extract?

Answer 3

to neutralize the tannic acid and other acidic compounds in the tea leaves to keep them water soluble

Question 4

moves a solid soluble natural product into the liquid solvent

Answer 4

solid/liquid extraction

Question 5

What are four characteristics of an ideal organic solvent?

Answer 5

• low boiling point
• shouldn’t react with solute or other solvents
• shouldn’t be toxic or highly flammable
• should not be miscible with water

Question 6

What is the purpose of the recrystallization in the experiment?

Answer 6

the purified caffeine is allowed to crystallize after a marginal solvent is added

Question 7

Why is it important to note the tea brand used?

Answer 7

different brands will have different amounts of caffeine

Question 8

what is the purpose of the sold/liquid extraction in the experiment?

Answer 8

to move caffeine from the leaves to the aqueous water layer

Question 9

Why does the water used need to be distilled water?

Answer 9

distilled water doesn’t contain ions like tap water does

Question 10

what is the purpose of sodium carbonate in the experiment?

Answer 10

sodium carbonate (base) ensures that the caffeine and organic acids are deprotonated

Question 11

why do we boil the water/sodium carbonate solution in the solid/liquid extraction?

Answer 11

greater solubility occurs at higher temperatures

Question 12

Why do we use a plastic centrifuge tube instead of a glass tube?

Answer 12

Plastic is more resistant to pressure changes in comparison to glass and is far more flexible.

Question 13

what is the purpose of methylene chloride in the liquid/liquid extraction

Answer 13

serves as the organic layer (bottom layer) in the experiment (immiscible to water)

Question 14

Why must we shake the tube gently as to not form emulsions?

Answer 14

These liquid/liquid emulsions take a millennia to settle. Literally, it will take a week.

Question 15

Why do we separate the methylene chloride into three portions and perform the liquid/liquid extraction 3 times?

Answer 15

The first time will pull the majority of the caffeine out of the aqueous layer into the organic layer.
The second and third time will pull out the remaining caffeine into the organic layer, to be extracting via pipette.

Question 16

Why do we need to release the vapor pressure?

Answer 16

it will allow the solutions to settle faster

Question 17

Why must we add the organic layer to a pre-weighed beaker?

Answer 17

This is to determine the volume of organic liquid collected via pipette.

Question 18

Why do we need to make sure there are no brown specks in the bottom of the organic layer beaker?

Answer 18

If the specks remain, the purity of the caffeine is jeopardized.

Question 19

Why do we place a watch glass over the beaker and place it under the hood?

Answer 19

to allow the methylene chloride (solvent) to evaporate from the organic portion

Question 20

What is the final step in caffeine extraction?

Answer 20

recrystallization of crude caffeine

Question 21

Why do we add the isopropyl alcohol dropwise?

Answer 21

This will maximize the recrystallization yield of caffeine

Question 22

Neutralization of tannic acid with sodium carbonate equation

Answer 22

2C76H52O46 + 25Na2CO3 → 2C76H27O46Na25 + 25H2CO3

Question 23

Benzoic Acid Neutralization

Answer 23

C6H5COOH(s) + NaOH(aq) -> C6H5COONa(aq) +H2O(aq)

Question 24

p-Nitroaniline neutralization

Answer 24

C6H6N2O2 (s) + HCl (aq) -> C6H6N2O2H+ + Cl-

Question 25

Naphthalene extraction

Answer 25

C10H8(aq) +CH2Cl2 (aq) -+39.6*-> C10H8(aq)