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Organic chemistry I Lab Final

front 1

When is Fractional distillation used instead of simple distillation? Which method is more efficient?

back 1

When the boiling points of two compounds differ by less than 40 °C, they cannot be separated by simple distillation. Fractional distillation is more efficient

front 2

What is the function of the glass beads packed in the fractionating column during fractional distillation?

back 2

They provide a larger surface area to perform a series of repeated distillations in the column for separation of compounds.

front 3

Where should the bulb of the thermometer be placed during distillation?

back 3

Right below the side-arm of the distilling head.

front 4

List 4 errors that can lead to incorrect melting points?

back 4

  1. The packed sample is not finely powdered.
  2. The sample is heated too rapidly, leading to inaccurate melting point reading.
  3. Poor heat transfer due to the placement of too much sample into the capillary tube.
  4. Mistaking sweating for melting of the sample. Melting is the first appearance of liquid within the bulk of the sample itself.

front 5

Describe an ideal solvent for recrystallization of compound X?

back 5

-X is insoluble at room temperature but soluble at the solvent’s boiling point

- The solvent must either completely dissolve all the impurities at all temperatures or it must not dissolve the impurities at all

- The melting point of X is higher than the solvent’s boiling point.

front 6

What is the purpose of using activated carbon during recrystallization?

back 6

Activated carbon is used to remove colored impurities because it can absorb the impurities on its surface and then can be left behind in the filter paper.

front 7

If a student uses too much activated carbon, what can be the consequences?

back 7

Reduction of percent recovery since it can also absorb the compound to be purified.

front 8

During recrystallization, what are some options if you see no crystal after cooling down the solution to room temperature?

back 8

-Cool in ice bath
- Scratch surface with glass rod - Add a pure seed crystal
- Concentrate by evaporation

front 9

Indicate at 2 ways to visualize a TLC spot which is invisible under UV light.

back 9

Iodine Chamber or Stain (Dye)

front 10

What is characteristic of compounds that travel far on TLC plates?

back 10

They are less polar

front 11

What is characteristic of compounds that do not travel far on TLC plates?

back 11

They are more polar

front 12

When reacting Br2 with Hexane, what is observed?

back 12

Solution remains red

front 13

When reacting Br2 with Cyclohexene, what is observed?

back 13

Solution becomes colorless

front 14

When reacting KMnO4 with Hexane, what is observed?

back 14

Solution remains purple

front 15

When reacting KMnO4 with Cyclohexene, what is observed?

back 15

A dark brown or black precipitate is formed

front 16

When reacting H2SO4 with Hexane, what is observed?

back 16

No heat is generated

front 17

When reacting H2SO4 with Cyclohexene, what is observed?

back 17

Heat is generated

front 18

In Gas Chromatography, how does Boiling point influence retention time?

back 18

Compounds with low boiling points have faster retention times

front 19

In Gas Chromatography, how does polarity influence retention time?

back 19

More polar compounds have slower retention times

front 20

Define Theoretical Plate

back 20

Each condensation and revaporization that occurs on a fractioning column is a theoretical plate

front 21

What is the retention time trend for the following compounds: butane, diethyl ether, and butanol in a Carbowax (medium-high polarity) column?

back 21

Butanol > diethyl ether > butane

front 22

What is the reaction rate order for the Lucas test?

back 22

3o>2o>1o

front 23

What is the reaction rate order for the TCICA test?

back 23

2o>1o>3o

(3o is unreactive)

front 24

What is the Lucas reagent?

back 24

ZnCl2 in HCl and H2O

front 25

What is formed in the TCICA reaction?

back 25

A Isocyanuric acid precipitate and a carbonyl group

front 26

What are Derivatives?

back 26

Unknown alcohols can be reacted to give stable, crystalline compounds called derivatives

front 27

Why are derivatives useful?

back 27

Stable, crystalline derivatives can be used to identify unknown alcohols by comparing their derivative melting point with literature values.

front 28

What is the purpose of Trituration in the Grignard lab?

back 28

Trituration is grinding of the crude product using petroleum ether in order to remove Biphenyl.

front 29

Why does the addition of sodium or potassium Iodide catalyze SN2 reactions of alkyl halides?

back 29

Because Iodide is both a good leaving group and a good nucleophile.

front 30

Define Extraction

back 30

Selectively dissolves the desired compound into an appropriate solvent.

The desired compound is in the extract

front 31

Define Washing

back 31

Removes impurities by dissolving them in an appropriate solvent.

The desired compound is left behind

front 32

Alcohol ease of dehydration dehydration order

back 32

3o>2o>1o

front 33

Why is a slow rate of heating necessary to obtain an accurate melting point?

back 33

-It will let the apparatus, capillary, and compound all reach the same temperature at the same time.

-A slow rate of heating will spread heat evenly throughout the sample to reach an accurate mp

front 34

What is the difference between evaporation and boiling?

back 34

-Evaporation occurs below the BP.

-Boiling occurs when the pressure of evaporating gas equals the pressure of the surrounding gas

front 35

Why should you not add boiling chips to an already hot liquid?

back 35

Boiling will be too vigorous and out of control

front 36

Describe the recrystallization procedure.

back 36

  1. Choose correct solvent
  2. Dissolve crude product in just enough of boiling hot solvent with 5% excess
  3. Cool filtrate to RT using an ice bath.
  4. Filter, separate and wash crystals on filter.

front 37

In a solution of acetanilide, p-toluic acid, and p-tert-butylmethyl ether, what can be extracted using NaHCO3?

back 37

p-toluic acid

front 38

Define Eutectic Composition

back 38

Both compounds are in equilibrium with the liquid

front 39

Define Eutectic temperature

back 39

Lowest possible melting point for a mixture of X and Y

front 40

Why would you choose methanol over water for a recrystallization solvent?

back 40

The boiling point of methanol is lower

front 41

In the Extraction lab, what is the purpose of heating up and cooling down the mixture before adding HCl?

back 41

It helps get rid of trace amounts of TBME which can prevent recrystallization

front 42

Which law takes into account the mole fractions of the compounds?

back 42

Raoult's Law

front 43

When 2 compounds are miscible, what law should be used to determine overall pressure?

back 43

Raoult's law

front 44

When 2 compounds are immiscible, what law should be used to determine overall pressure?

back 44

Dalton's law

front 45

Why is steam distillation used preferable to simple distillation for isolating natural product with a high boiling point?

back 45

It allows for distillation at lower temperatures which avoids decomposition of the product

front 46

How should be characteristic of a solvent for gas chromatography?

back 46

The solvent should be more volatile than the compound of interest.

front 47

What is the difference between steam distillation and codistillation?

back 47

-Simple distillation is for miscible liquids and does not involve water, while steam distillation is for immiscible liquids and uses water.

-Steam distillation is a form of codistillation that uses water.

front 48

What form of distillation is used for immiscible liquids?

back 48

Codistillation. Steam distillation is a type of codistillation.

front 49

For extraction, which solvents are more dense than water?

back 49

Dichlorromethane

front 50

For extraction, which solvents are less dense than water?

back 50

Hydrocarbons and ethers

front 51

What solvents are typically used for Sn1?

back 51

Polar protic (MeOH, EtOH)

front 52

What solvents are typically used for SN2

back 52

Polar aprotic (Acetone, DMSO, DMF, MeCN)

front 53

When removing impurities during the recrystallization lab, what are the consequences of not preheating the gravity filtration apparatus?

back 53

It may cause premature crystal formation on the filter paper.

front 54

In the recrystallization lab, what are the consequences of adding too much boiling solvent?

back 54

It will inhibit crystal formation because there will be difficulty in forming the crystal lattice if solvent particles are getting in the way.

front 55

What is the purpose of boiling chips?

back 55

Boiling chips facilitate a smooth boil, preventing boiling over and uneven bubbles.