Lab

Question 1

what experiment is an example of electrophilic addition to an alkene

Answer 1

bromination of trans-stilbene

Question 2

an insoluble solid that emerges from a liquid

Answer 2

precipitate

Question 3

the formation of a solid from homogenous solution. this solid is often the product from a chemical reaction

Answer 3

crystalization

Question 4

a purification technique, the product of a chemical reaction usually contains impurities

Answer 4

recrystalization

Question 5

recrystilization technique:

Answer 5

• dissolve impure solid in hot solvent
• allow solution to cool, crystalizing the solid
• leaving impurities dissolved in solvent

Question 6

steps in recrystalization ::

Answer 6

1. choose the solvent
   
   • solvent should not dissolve in cold or RT solvent, but hot solvent
2. dissolving the solute
   
   • use mim amount of hot solvent to make a saturated solution.
   • solute is dissolved when solution is clear
3. decolorization of solution
4. removing suspended solid (filter to remove any insoluble impurities)
5. crystilization the solid (cool solution slowly)
6. collecting and dying crystals ( use vacuum filtration)

Question 7

what is the percent recovery equation?

Answer 7

% recovery= final mass (g)/inital (g) * 100

-cannot be over 100%

Question 8

purification-Separation technique

Answer 8

distillation

Question 9

distillation involves _______ and _________ phase changes

Answer 9

liquid and vapor

• vaporization = L–>V
• condensation = V–>L

Question 10

a liquid mixture is heated to its bp so that vapor is condensed and the ____________ is separated from original mix

Answer 10

condensate

Question 11

as distillation progresses, the vapor is enriched with the more ________ component and the “pot” is enriched with the higher boiling componet

Answer 11

volatile

Question 12

3 types of distillation

Answer 12

simple, fractional, steam

Question 13

only one componet of mixture is volatile (evaporates readily at normal temps and pressures)

Answer 13

simple distillation

Question 14

spec 20 advantages and limitations

Answer 14

sensitive, fast, simple, inexpensive

limitations: micro-tech, standards are necessary to identify unknowns.

Question 15

relationship between absorbance and concentration

Answer 15

BEERS LAW

Question 16

BEERS LAW equation

Answer 16

A=EIC
A=absorbance
E=molar absorbancy, a constant
I=path length 
C=concentration of solution

Question 17

percent purity equation

Answer 17

%purity= Ai-Af/Ai*100

Question 18

steps of Thin Layer Chromotography (TLC)

Answer 18

1. use pencil to # bottom of TLC plate with samples
2. mark bottom of plate with straight line 1cm above bottom
3. place plate inside TLC chamber and put lid on it. DON’T MOVE.
4. remove plate when solvent has traveled 3/4th of the plate

Question 19

Rf= ??

Answer 19

retention factor= single dot(distance traveled by compound)/total distance solvent traveled

Question 20

3 factors of Rotovap

Answer 20

1. vacuum lowers the pressure which lowers the bp of solvent
2. heated water bath allows the solvent to readily evaporate
3. rotation gives larger surface area

Question 21

-a ration of concentrations of a compound in the 2 phases of a mix 2 immiscble liquids

Answer 21

partition coeficent

Question 22

partition coeficient =?

Answer 22

Keq= [com X] organic phase/ [com x] aqueous phase

Question 23

ratio that measures how hydrophobic or hydrophilic a compound is…

Answer 23

partition coeficient

Question 24

dissolving a compound in a mixture of two immiscible solvents so that the compound dissolves into both solvents.
-exploits solubility differences in organic and aqueous solvents

Answer 24

liquid liquid extraction= Seperation technique

Question 25

process often used to isolate products from natural materials -most organic compounds are insoluble in water, so organic solvents are used to extract

Answer 25

solid liquid extraction

Question 26

purpose of melting point

Answer 26

- test if the substance is pure - to help identify a substance - generally has a melting range

Question 27

what is it possible for % recovery to exceed 100%?

Answer 27

- adding too much product - using wrong solvent to wash out vial into vacuum filtration - not weighing the weigh paper in advance

Question 28

What kind of reaction is stilbene from the bromination of trans-stilbene lab?

Answer 28

Not steriospecific, since small amount of di-stilbene dibromide are also made. --the formation of meso-stilbene dibromide occurs via the NUCLEOPHILIC ATTACK of bromide on the intermediate cyclic bromonium ion

Question 29

what does in situ mean?

Answer 29

in the reaction mixture

Question 30

SN1 reaction..

Answer 30

``` s= substitution N= nucleophilic 1= unimolecular ```

Question 31

for rotation to occurs around a _____ _______ forming a new isomer, 1. pi bond must break, 2. rotation takes place around the C-C sigma bond, and 3. pi bond re forms

Answer 31

double bond

Question 32

factors favor the rate of SN1 reactions:

Answer 32

1. nature of the alkyl halide substrate (rate of rxn increases as stability of the carbocation intermediate increaes) 2. nature of the nucleophile (only [RX] affects rate) 3. nature of the leaving group (how easily the C-X bond breaks) 4. solvent (polar solvents)