1. 2016 Summer Session 1 Kevin Chen
Chem 51LB Week 3
2016 Summer Session 1
Kevin Chen

2. Lecture Outline Miscellaneous announcements
Experiment #4: Acid/base extraction

3. Sapling! Incomplete Sapling = NO LAB!
No lab means no in-lab points/TA discretion (15 pts)
Can still do the post-lab reports
TA will assign you data to use for the report

4. Proper waste disposal
We have our first case of “glass waste” in regular trashcan
This is a major safety violation
Next time, EVERYONE in the section will lose a letter grade

5. Experiment #4 Acid/base extraction
Given: One unknown acidic and one neutral organic compound (fluorene) as a mixture
Goal: Separate the two organic compounds (acidic and neutral) with separatory funnel extraction then recrystallization and melting point
End game: Identify the acidic compound in the mixture and confirm the identity of fluorene

6. SAFETY ANNOUCEMENT!
Strong acid (HCl) and base (NaOH) are being used  BE CAREFUL!
Evaporating diethyl ether using INDIRECT HEAT, heating directly on the hot plate means FIRE!
The TAs will discourage bad lab techniques by taking points off from people who decides to ignore these warnings

7. Separatory funnel
Needs two immiscible solvents (one is almost always water)
Organic solvent versus water (aqueous)
Think oil versus water

8. IMPORTANT SAFETY ANNOUNCEMENT
Pressure can build up when one shakes a full separatory funnel
IT CAN EXPLODE!!!
VENT OFTEN!!!

9. Density is the key! There are two layers Which one is on top? Organic
Aqueous
Which one is on top?
Density is the key!
Lighter of the two immiscible liquid will be the top layer, which means most organic solvents
EXCEPT… methylene chloride aka dichloromethane aka DCM

10. Like dissolves like
Uncharged organic compounds are soluble in organic solvents
Charged organic compounds and ions are soluble in aqueous solution
Acidic compounds like carboxylic acid can be deprotonated to become negatively-charged carboxylate
Basic compounds like amine can be protonated to become positive-charged ammonium

11. Changing protonation state
Protonation state of a compound can be changed, How? pH
Protonation at low pH
Deprotonation at high pH
So why is this important?!?
An acidic compound is NOT charged at low pH and is charged at higher pH (greater than its pKa)
A basic compound is NOT charged at high pH and is charged at lower pH (lower than its pKa)

12. How do you change pH???
There are two solvents, organic and aqueous (which is water)
Water is the obvious choice!
Add acid  aqueous layer becomes acidic
Add base  aqueous layer becomes basic
Changing pH means changing solubility of the organic compounds!

13. Example: Aqueous solution at pH = 2
What layer would these compounds be in?
Acidic compound (carboxylic acid)
Basic compound (amine)
Neutral compound (cyclohexane)

14. Example: Aqueous solution at pH = 2
You should answer this question first… are these organic compounds charged at pH = 2?
Carboxylic acid  still neutral
Amine  positively-charged ammonium
Cyclohexane  still neutral

15. Example: Aqueous solution at pH = 2
Carboxylic acid  organic layer (because it is not charged)
Ammonium  aqueous layer (because it is positively-charged)
Cyclohexane  organic layer (because it is not charged)

16. Additional notes on extraction
Label all your glassware!
Always keep track of which layer (organic or aqueous) that the organic compounds (acidic and neutral compound) are in
Eventually, the organic solvent needs to be removed, which means evaporation with heat
SAVE EVERYTHING UNTIL THE END!