Separation Techniques

Question 1

Extraction goal:
- phase of reactants
-

Answer 1

Goal: to separate aqueous mixtures
- partition compound between two liquid phase
Phase 1: polar aqeous
Phase 2: Nonpolar organic

Question 2

Dichloromethane, chloroform, diethyl ether, ethyl ester

Answer 2

Types of organic solvents in extraction

Question 3

Aqueous phase of extraction and why?

Answer 3

Water, highly polar, immisible in organic solvents

Question 4

What phase settles to the bottom in extraction?

Answer 4

More dense phase, usually aqueous water

Question 5

Can you separate neutral molecule with uncharged acidic and basic components?

Answer 5

Yes with the addition of base, you can deprotonate the acid or addition of acid, you can protonate the base
- this changed substance will be dissolved and extracted in aqueous layer

Question 6

Can you separate molecule with two similar components, say two uncharged acids?

Answer 6

Yes, if one acid is stronger than the other it will be deprotonated faster
- weak base can deprotonate stronger acid (negatively charged) extracted in aqueous layer

Question 7

What is the uncertainty with distillation?

Answer 7

• even before a molecule reaches its boiling point, some of the liquid is turning into gas
• thus not sure that the lower BP molecule is fully distilling first

Question 8

What is the process of overcoming uncertainty in distillation?

Answer 8

Multiple distillation procedures to remove impurities

Question 9

What is the min level of BP difference ion simple distillation?

Answer 9

25 C or more

Question 10

What does fractional distillation due?

Answer 10

• fractionated column makes it harder for vapor molecules to travel all the way up and decondense
• can separate two molecule with closer BP

Question 11

Phases of chromatography:

Answer 11

Mobile: liquid or gas phase

Stationary phase

Question 12

TLC is what

Answer 12

Thin layer chromatography:
Stationary: adsorbant silica polar gel (can H-bond)
Mobile: non-polar solvent, hexane (elluent)

Question 13

How do types of molecules move within TLC?

Answer 13

Non-polar move faster and farther with solvent up apparatus

Polar: move solar and less far due to bonding with aparatus

Question 14

Column chromatography phases:

Answer 14

Stationary phase: solid adsorbent at bottom of column
Sample of interest added
Mobile phase: solvent, poured through column pushing sample

Question 15

How are sizes eluded in size exclusion chrom?

Answer 15

Largest pass through more easily then small and then smallest

Question 16

Ion exchange chrom defintions:

Cation and Anion traps what and what is the stationary phase:

Answer 16

Cation exchange traps cations
- stationary is anion:

Anion exchange traps anions
- stationary is cation:

Question 17

Affinity chromatography, what happens to the compound of interest?

Answer 17

Ligands make up stationary phase:

• compound of interest binds to ligands on the sides of column
• uninterested items pass through

Question 18

How do you get the compound of interest elluted from affinity chrom?

Answer 18

• Cause bound compound of interest to dissociate

- useful for proteins, bio macro molecules

Question 19

Gas chromotography phases:

Answer 19

Gas-liquid
Mobile phase: gas like N or He
Interest phase: vaporized
Stationary phase: liquid or polymer coating

Question 20

What does ellutants of gas-liquid chromotography say?

Answer 20

Each peak is a different compound, width/area is amount of compound
- smaller (lower BP) are sooner, earlier peaks

Question 21

What is difference of HPLC?

Answer 21

High performance liquid chromotography
Mobile phase: liquid flows through
Stationary phase: solid

Distinguishable: extremely high pressures to move solvent through column compared to gravity in regular column

• improve interaction of stationary phase with solutes floating (can use smaller solutes)
• can help with greater separation of solutes

Question 22

How do molecules move through HPLC vs revere phase HPLC?

Answer 22

• non polar move faster and farther due to interaction with mobile phase
• polar molecules move slower due to increased interactions with stationary phase

Reverse phase: non polar stationary (hydrocarbon chains)
- polar mobile phase and polar molecules move faster

Question 23

What is important factor to consider in recrystallizaitons?

Answer 23

Solvent of choice:

- Desired product soluble at high temp, insoluble at low temp

Question 24

What is the initiation step of recrystallization?

Answer 24

• Nucleation via seed crystal initiates process
• Scratch side of flask, rough seed helps form
• usu repeat multiple times to reduce impurities

Question 25

What is last step of recrystallization?

Answer 25

Filtration of liquid solid mixture, left with desired product

Question 26

What is the most successful method for extracting methanal from aqueous solution?

Answer 26

Serial extractions are more effective than single extraction
- answer choices with volume amounts comparable, most successive extractions is best