quiz 2 overview

Question 1

caffine procedure

Answer 1

bottom layer: dichloromethane
top layer: water

1. use rocking motion to mix
2. 30ml of dichloromethane extracted
3. another of dichloromethane extracted
4. dry 60 ml w 2g of anhydrous sodium sulfate
   –wait 10 min + occasionally swirl
5. gravity filter
6. scrape white caffeine into a 100 RBF

Question 2

mobile/ stationary phases of HPLC

Answer 2

mobile: liquid(35% acetonitrile & 65% water)
stationary: particles of silicia

-reverse phase
stationary: nonpolar
mobile: polar

Impurity:polar will reach detector way ahead

No polar: hits stationary phase way of Ayer caffeine

Question 3

why use HPLC instead GC for caffine

Answer 3

HPLC is used because caffine is not volatile/ decomposes on heating

HPLC uses a UV detector and caffeine has a strong YV absorption

Question 4

calculate % yield of acetaminophen

Answer 4

experimental
_________________x 100
theoretical

theoretical:
(mole of p-aminpehnol*151.1)

Question 5

Reasons to use TLC

Answer 5

1. to follow the process of a reaction

2.check purity of a sample

3.to do a preparative separation by column chromatography & need to fund a suitable solvent sys

Question 6

calculate Rf value + what happens to the value if mehanol was added to solvent

Answer 6

distance traveled by sample
_____________________________
distance traveled by solvent

methanol is polar=>Rf value will get smaller

general behavior:
-polar will migrate slower (closer to bottom line)
-least polar wil travel faster (further)