Lab Final Review

Question 1

Chromatography separates on basis of?

Answer 1

Polarity
Capillary Action

Question 2

Where does the waste go for the disposal of solvents and excess spinach extract?

Answer 2

Nonhalogenated; solid waste

Question 3

What is the importance of the folded filter paper in TLC chamber?

Answer 3

Improve Reproducibility

Question 4

Determine the Rf values of compounds A,B,C?
A - 3mm
B - 9mm
C - 5mm

Answer 4

0.2,0.8,0.4

Question 5

Which compound is the most polar? The least polar?

Answer 5

B<C<A

Question 6

What would you expect to happen to the Rf values if you used acetone instead of hexanes as the eluting solvent?

Answer 6

Acetone is polar, all Rf would increase (travel higher up plate)

Question 7

What could happen if you spot too much of a compound on the TLC plate?

Answer 7

Tailing/streaking/dragging

Question 8

The presence of impurities affects the melting points of a sample in two ways is?

Answer 8

Broadens/widens
Depresses (lower)

Question 9

What is the most important component of the Mel-Temp apparatus?

Answer 9

Aluminum heating block (if it doesn’t work it won’t heat)

Question 10

All melting point capillaries should be disposed in?

Answer 10

Glass Waste

Question 11

The melting point of a crystalline solid should be?

Answer 11

Narrow/sharp/precise
reproducible

Question 12

The factors to determine a good solvent for recrystallization are?

Answer 12

1) Inert
2) Desired compounds insoluble at room temperature
3) Impurities should be either soluble or insoluble at ALL temperatures
4) Sufficiently volatile (easy to evaporate)

Question 13

Name the solvents for recrystallization and their boiling point

Answer 13

Hexanes (69°), Ether (34.6°), Dichloromethane (39.6°), Ethyl Acetate (77.1°)

Question 14

What is a common with petroleum ether and ligroin

Answer 14

Nonpolar, Hydrocarbon mixtures (like hexanes)

Question 15

The method used for separation and purification of volatile liquids is referred to as?

Answer 15

Distillation (Fractional or Simple)

Question 16

What is a distillate?

Answer 16

Compound(s) you distill and collect

Question 17

How can you define a boiling point of a liquid?

Answer 17

Temperature at which liquid is in equilibrium with gas/vapor

Question 18

What is the major difference between simple distillation and fractional distillation in terms of apparatus used?

Answer 18

Fractionating column with high surface area (use this for compounds with close/similar boiling points)

Question 19

What are the factors for efficient fractional distillation?

Answer 19

1) length/height of column
2) Surface area of packing material
3) Difference in boiling point
4) Rate of heating

Question 20

In liquid-liquid extraction, the choice of solvents must be?

Answer 20

1) Immiscible (doesn’t mix)
2) Different density

Question 21

What are the common solvent pairs to use for extraction?

Answer 21

Water + Organic solvent
Chlorinated (CH2Cl2, CHCl3, CCl4)
Dense (Halogens are heavy)

Question 22

If you have an organic solvent soluble amine, what kind of reagent could you add to form a water soluble salt?

Answer 22

Add acid (like HCl) because amines are basic. Form the ammonium salt
RNH2 + HCl -> RNH3 Cl (aqueous)

Question 23

What instrument is used for determination of optical rotation?

Answer 23

Polarimeter

Question 24

Two enantiomers in equal concentration is referred to as?

Answer 24

Racemate

Question 25

The process of isolating a single enantiomer from racemate is called?

Answer 25

(Chiral) resolution

Question 26

Enantiomers have similar/identical… Whereas diastereomers have different what?

Answer 26

Physical properties EXCEPT rotation of polarized light

Question 27

Dehydration mechanisms involve what?

Answer 27

1)Protonation (to form good leaving group)
2) Loss of water
3)Elimination (conjugate base of the acid used to protonate in first step)

Question 28

What are the tests (and reagents used) that can give evidence (presence or absence) of alkene and alkyne in a compound

Answer 28

1) Bromine Test (if alkene present, colorless, if not, RED)
2) Bayer test (KMnO4, if alkene present, brown (MnO2), if absent, purple (KMnO4)

Question 29

Bromine test gives positive result with color changes from _ to _?

Answer 29

Red/Brown to Colorless/Clear

Question 30

The waste for Bayer Test is disposed into _ container and why?

Answer 30

KMnO4, Heavy Metal (Mn)

Question 31

What factor is needed to generate more cyclohexene?

Answer 31

Add acid and heat

Question 32

Why is vigorous stirring important for preparation of suberic acid?

Answer 32

Reaction is biphasic (water and organic), phase transfer catalyst brings MnO4- into organic to do the oxidative cleavage

Question 33

The reaction of permanganate ion with double bond is a form of?

Answer 33

Electrophilic addition across an alkene

Question 34

What is a vicinal diol?

Answer 34

Any diol in which the two hydroxy functional groups are attached to adjacent carbon atoms

Question 35

Why is Aliquat 336 used instead of a common salt?

Answer 35

Organic Water Solute

Question 36

What is the color and oxidation state of manganese in potassium permanganate? What is the color and oxidation state of manganese in manganese oxide? Is the a reduction or a oxidation of manganese?

Answer 36

Potassium ( Purple )
Oxide (Brown 4+)

Question 37

The formation of 2- Bromobutane from 2- butanol involves?

Answer 37

1) Protonation to form good leaving group
2) Loss of Water
3)Nucleophilic attack of bromide

Question 38

The order of reactivity is based on formation of?

Answer 38

Stable Carbocation

Question 39

What should be done if the is spilling of bromine water?

Answer 39

Avoid breathing vapors from spill. If possible, confine the spill to a small area using a spill kit or absorbent material.

Question 40

Why is cyclohexene added at the end of the reaction?

Answer 40

Excess Br

Question 41

What happens when bromine is added to trans-cinnamic acid?

Answer 41

formation of two different pairs of enantiomers