Lab final

Question 1

What are the step for recrystallization

Answer 1

Find good solvent
Heating
Precipitation
Filtration 
Drying

Question 2

What does it mean to find a good solvent in recrystallization

Answer 2

find a solvent with a high bp but not too high that evaporation takes too long (50-80 C)

Question 3

What does heating mean in recrystallization

Answer 3

add solvent to organic acid and heat until solid is fuly dissolved

Question 4

What does precipitation mean in recrystallization

Answer 4

slower the process, the better the yield. Use an ice bath to cool further

Question 5

What does filtration mean in recrystallization

Answer 5

vacuum to get rid of liquid, rinse so that soluble impurities are removed

Question 6

What does drying mean in recrystallization

Answer 6

air is pulled over crystal and they are then put in oven

Question 7

What properties affect separation in GC

Answer 7

Polarity and boiling point. Higher polarity causes substance to interact with columns more and higher bp have higher retention time

Question 8

what substrate/solvent will be in each layer of extration and why

Answer 8

Acids/bases will partition into an aqueous layer if charged but if there is no separation then an acid/base needs to be added so that there is a loss/gain of electron causing them to partition (aqueous layer is on top)

Question 9

Why do we dry reagents in extraction

Answer 9

to remove organic solvents and water from substances to leave them pure

Question 10

What is the melting point

Answer 10

temp at which substance is at equilibrium at standard pressure (more of a range)

Question 11

How do impurities affect melting point

Answer 11

Lower melting point and broadens range

Question 12

How do you calculate Rf values

Answer 12

Distance spot traveled divided by distance solvent traveled

Question 13

How do you separate and isolate two enantiomeres

Answer 13

Decant methanol, transfer crystals to a separatory funnel, extract with DCM, and separate and dry organic layer

Question 14

What does it mean to decant methanol when separating enantiomers

Answer 14

Liquid is poured from one container to another, leaving sediment at the bottom of the first layer. Doing so with methanol, separates amine tartrate crystals that will be used.

Question 15

What does it mean to transfer crystals to a sepratory funnel when separating enantiomers

Answer 15

Set up sepratory funnel, put crystals in, add water to dissolve some of the crystals, add NaOH then swirl to further dissolve crystals

Question 16

What does it mean to extract with DCM when separating enantiomers

Answer 16

Add DCM to funnel and shake while venting to ensure all solids are dissolved. This will create two layers with the lower one having the free amine

Question 17

What does it mean to separate and dry organic layer when separating enantiomers

Answer 17

Lower layer is drained along with amines in it. DCM is added to the separatory funnel and then shaken and allowed to separate. The lower layer is then added to previous extraction. K2CO3 is added to extraction to dry it and then filtered to further dry and then put into the roto vap

Question 18

How does polarimetry work

Answer 18

Measures the direction (CW or CCW) and extent to which a sample interacts with polarized light. The difference in enantiomers will interact with polarized light in different fashions

Question 19

What is the equation for IHD

Answer 19

C x 2 + 2 + N - H - X all dividied by 2