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Ochem Lab - CHE 3238 > Final Exam > Flashcards

Final Exam Flashcards

1
Q

Arrange these eluent solvents from least polar (1) to most polar (4)

diethyl ether, hexanes, ethyl acetate, methanol

A
  1. hexanes
  2. diethyl ether
  3. ethyl acetate
  4. methanol
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2
Q

In TLC, the eluent is the ___________
phase

A

mobile

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3
Q

Fourrier Transform Infrared Spectroscopy (FTIR) observes what kind of molecular motion?

A

Vibrations

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4
Q

FTIR spectra are given in what units?

A

wavenumbers (cm-1)

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5
Q

When you are done with your IR, you should clean your plates with:

A

acetone and kimwipes (WATER NEVER NEAR!!)

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6
Q

Water in your sample would show as…

A

A large, broad peak at 3500 cm-1

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7
Q

The region of the FTIR spectrum with wavenumbers under 1500 cm-1 is generally called the…

A

fingerprint region

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8
Q

(T/F):

The salt plates used in this experiment do not absorb IR radiation

A

True- The plates are made of sodium chloride and thus do not contain any covalent bonds.

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9
Q

Out of the following, which are vibrational modes of molecules

Symmetric stretching
Rocking
Twisting
Bending
Asymmetric stretching
Wagging

A

All of these are vibrational modes of molecules

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10
Q

True or false: FTIR can visualize ALL covalent bond vibrations.

A

False- FTIR requires a bond to have a dipole moment in order to be visible. Symmetrical bonds are therefore faint or not visible (i.e.: C-C bonds).

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11
Q

True or False: Melting point should be recorded as an exact temperature.

A

This is false, melting point should be recorded as a temperature range.

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12
Q

You have a solid sample you are using for a melting point measurement. Your solid should…

A
  • be dry
  • reach 2-3 mm up the capillary
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13
Q

What influences melting point?

A

purity of the sample

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14
Q

When doing a rough melting point, you want to set the ramp rate to ____________. After this measurement is finished, you should set the start temperature ____________ your observed rough melting point and chose a ramp rate of ____________ to obtain your precise melting point measurement.

A

When doing a rough melting point, you want to set the ramp rate to 10ºC/min. After this measurement is finished, you should set the start temperature slightly closer to your observed rough melting point and chose a ramp rate of 1ºC/min to obtain your precise melting point measurement.

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15
Q

The melting point range of a purer compound will be

A

higher, narrower

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16
Q

The melting point range of a impure compound will be

A

broader, lower

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17
Q

True or False: You can dispose of used melting point capillaries in the normal trashcan.

A

False - used melting point capillaries should go in the broken glass waste

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18
Q

True or False: You cannot reuse melting point samples.

A

This is true! Once melted, it is not recommended to re-use a sample as some decomposition could have occurred that would affect its purity, and therefore melting point.

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19
Q

NMR spectrometers contain….

A

a magnet

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20
Q

(T/F):

All types of atoms are visible by NMR

A

False

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21
Q

Which of these functional groups would be most deshielded (high ppm value)?
- benzene ring
- CH2Cl
- alkene
- aldehyde

A

aldehyde

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22
Q

Which of the following affect a 1H nucleus’ chemical shift, in ppm?
- Electronegative atoms
- Magnet strength
- Aromatic rings
- Resonance structures

A

Electronegative atoms
Aromatic rings
Resonance structures

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23
Q

(T/F):

You can use normal chloroform (CHCl3) as the solvent for your NMR sample

A

False

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24
Q

Why does carotene move higher up the TLC than other compounds such as chlorophyll?

A
  • because it is less polar
  • because it does not interact strongly with the silica gel
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25
Q

If your TLC plate had used reverse phase silica gel, carotene would have the…

A

lowest Rf

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26
Q

Sort the following solvents into two categories: polar and non-polar

  • acetone
  • methanol
  • hexanes
  • ethyl acetate
A

Polar: acetone, methanol, ethyl acetate
Non-polar: hexanes

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27
Q

A TLC of my product gives a Rf of 0.37 using a 5:3 hexanes/ethyl acetate eluent. What would happen to the Rf if the eluent was changed to 3:1 hexanes/ethyl acetate?

A

It would decrease

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28
Q

What risk do you take if you do not rinse your TLC spotter between samples?

A

Contamination of your sample

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29
Q

You find in the lab two liquid samples with their labels erased! You know one is an aldehyde and one is a ketone. Which of the techniques that you used in the Compound ID lab would be the most accurate in helping you figure out which sample is which?

A

NMR

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30
Q

True or false: The C-O bond vibration in isopropanol is a broad peak around 3300 cm-1

A

False - C-O bonds are actually in the fingerprint region. The broad peak at 3300 cm-1 is the O-H bond vibration!

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31
Q

You attempt to synthesize ibuprofen in the lab. You obtain a white solid which looks like ibuprofen, and melts at the correct melting point (75-77 °C). You mix the synthesized sample with pure ibuprofen, then take a melting point analysis of that mixed sample. Which of the following observations would prove to you that your synthesized sample is indeed ibuprofen?

A

The melting point of the mixed sample would remain 75-77 °C

32
Q

(T/F):

In a solution of pH 6, acetic acid (pKA = 4.5) will be protonated

A

False

33
Q

An ethyl acetate organic phase would

A

be above the aqueous layer

34
Q

A chloroform organic phase would

A

be below the aqueous layer - Dichloromethane has a density of 1.33 g/mL, and is heavier than water. It is not miscible with water and will not react with it, so it will form an organic phase below the aqueous phase.

35
Q

I have a mixture of 3 compounds: A is acidic, B is basic and N is nonacidic. If I treat my mixture with aqueous NaOH, which compound(s) will remain in the organic phase?

A
  • B (basic compound)
  • N (neutral compound)
36
Q

Which of the following are correct when using a separatory funnel for an aqueous extraction?
- Vent regularly
- Point the funnel towards the back of the hood when venting
- Shake the funnel outside the hood
- Remove the stopper before turning the stopcock to pour out the solution
- Rest the funnel on a ring stand
- Use your hand as a funnel stopper if you can’t find the glass one
- Remove the stopper to vent your funnel

A
  • vent regularly
  • Point the funnel towards the back of the hood when venting
  • Remove the stopper before turning the stopcock to pour out the solution
  • Rest the funnel on a ring stand
37
Q

Predict whether the organic compounds below would be majoritarily protonated or deprotonated at the given pH.
- Acetic acid in a solution of pH 2
- Aniline in a solution of pH 12
- Salicylic acid in a solution of pH 4
- Piperidine in a solution of pH 7

A
  • Acetic acid in a solution of pH 2 protonated
  • Aniline in a solution of pH 12 deprotonated
  • Salicylic acid in a solution of pH 4 deprotonated
  • Piperidine in a solution of pH 7 protonated
38
Q

Match the following waste to the appropriate waste stream

  • used TLC plates
  • organic phase containing caffeine
  • leftover brine
  • TLC samples of acetaminophen and aspirin in acetone
  • used but washed glass pipettes
A
  • used TLC plates -> Trash
  • organic phase containing caffeine> Nonhalogenated organic waste
  • leftover brine -> aqueous waste
  • TLC samples of acetaminophen and aspirin in acetone -> nonhalogenated organic waste
  • used but washed glass pipettes -> glass waste
39
Q

Column Chromatography using silica gel separates compounds

A

Polarity

40
Q

As opposed to a TLC, the eluent moves ….. in a chromatography column

A

downwards

41
Q

A flash column is faster than a normal gravity column thanks to the application of

A

Air pressure

42
Q

The construction of your column should include

A
  • top layer of sand
  • short plug of cotton
  • bottom layer of sand
  • layer of silica gel
43
Q

(T/F):

Each time you add eluent, you should elute the solvent completely out of the silica gel so it becomes dry again before adding more eluent.

A

False - your solvent should never go underneath the top layer of sand of your column.

44
Q

When doing a gradient elution you start your column with a ____________ eluent mixture and progressively ____________ polarity until your target eluent mixture is reached.

A

When doing a gradient elution you start your column with a nonpolareluent mixture and progressively increasepolarity until your target eluent mixture is reached.

45
Q

When evaluating an eluent for use in a column by TLC, the Rf of your desired compound should be…

A

0.3-0.5

46
Q

Order these solvent mixtures from least polar (1) to most polar (4)

  • 1:1 hexanes/ethyl acetate
  • 2:3 hexanes/ethyl acetate
  • 5:2 hexanes/ethyl acetate
  • 9:1 hexanes/ethyl acetate
A
  • 1:1 hexanes/ethyl acetate (4)
  • 2:3 hexanes/ethyl acetate (3)
  • 5:2 hexanes/ethyl acetate (2)
  • 9:1 hexanes/ethyl acetate (1)
47
Q

Match the following waste to its correct waste stream

  • Paper towels soiled with ethyl acetate and hexanes
  • Syringe containing silica gel and sand
  • Solutions from beakers/erlenmeyers 1-6
  • Water used to rinse the mortars and pestles
A
  • Paper towels soiled with ethyl acetate and hexanes -> Trash
  • Syringe containing silica gel and sand -> solid waste
  • Solutions from beakers/erlenmeyers 1-6 -> nonhalogenated organic waste
  • Water used to rinse the mortars and pestles -> aqueous waste
48
Q

(T/F):

When at reflux, the temperature inside the reaction flask is constant

A

True - It is constant and corresponds to the boiling point of the solvent.

49
Q

(T/F):

In a condenser, the water and reaction mixture are in physical contact and can mix.

A

False - The condenser is a specialized piece of glassware with two different “cavities”: one for the reaction and one for the coolant

50
Q

Reflux is observed when

A

the solvent drips steadily back into the reaction

51
Q

If I run a reaction at reflux in toluene, what temperature would my reaction be at?

A

110 °C - toluene boils at 110 °C, thus the refluxing reaction will remain at this temperature.

52
Q

On a reflux condenser, the cold water outlet tube should be connected to

A

the top port of the condenser

53
Q

The reaction I am running reacts A and B together to make product C. In my flask, I have 15 mmol of A and 20 mmol of B. How many equivalents of B are there compared to A? round to 2 decimal places

A

1.33 - A is the limiting reagent. moles B/moles A = 20 mmol/15 mmol = 1.33

54
Q

I am using 5 mL of a 2.5 M solution of NaOH. How many millimoles of NaOH does this correspond to? (use 3 significant figures)

A

12.5 (5 mL x 2.5 mol/L = 12.5 mmol)

55
Q

I calculated that my reaction could give me 250 mg of product, but only isolated 175 mg. What is my percent yield?

A

175 mg / 250 mg = 0.7 = 70%

56
Q

I have to use 382 mg of phthalic acid in a reaction. Using molecular weight, calculate the millimoles of phthalic acid this corresponds to, with 3 significant figures

A

Phthalic acid: 166.14 g/mol

382/166.14 = 2.30 mmol

57
Q

Match the following waste to the appropriate waste stream

  • pure tetracyclone solid
  • 2.0 M KOH in Ethanol
  • Filtrate from Hirsch funnel
  • TLC w/ tetracyclone, benzoin and benzil spots
A
  • pure tetracyclone solid -> solid waste
  • 2.0 M KOH in Ethanol -> nonhalogenated organic waste
  • Filtrate from Hirsch funnel -> nonhalogenated organic waste
  • TLC w/ tetracyclone, benzoin and benzil spots -> trash
58
Q

Organic bases generally contain which functional group?

A

amine

59
Q

You are looking at extracting a phenol-containing compound (pKA =10.5) from an organic phase and transfer it to the aqueous phase. Which of the following aqueous solutions can you use to perform this extraction?

A

1M NaOH, pH 14

60
Q

You are looking at extracting a pyridine-bearing compound (conjugate acid pKA = 4) from an organic phase and transfer it to the aqueous phase. Which of the following aqueous solutions can you use to do so?

A

1 M HCl, pH 1

61
Q

I can take my separatory funnel out of the fume hood to shake it.

A

False

62
Q

I don’t know which of my layers is water and which is my organic phase, and I’ve forgotten what solvent I used!
Which of the following observations would tell me that my top phase is my organic phase

A

I add a few drops of water to the top of my separatory funnel. The droplets pass through the top phase without mixing, then mix with the bottom phase

63
Q

True or False: you can use an acid-base extraction to separate your tetracyclone from leftover benzil or dibenzylketone.

A

False

64
Q

You plan a synthesis of tetracyclone using different quantities of Benzil and Dibenzylketone. 298.4 mg is the mass of benzil while 434.6 mg is the mass of dibenzylketone. What is the theoretical yield of the reaction, in milligrams? Use 1 decimal place.

A

545.7

65
Q

You used an eluent mixture of 9:1 hexanes/ethyl acetate for your TLC. What would happen to your RF values if you changed the eluent to 7:1 hexanes/ethyl acetate

A

all RF values would increase

66
Q

Distillation is a method of separation based on…

A

boiling point

67
Q

____________distillation is used to separate compounds with boiling points differing by over 100 °C

A

Simple distillation

68
Q

Fractional distillation requires the use of a fractionating column with increased ________ which allows for more vaporization/condensation cycles.

A

surface area

69
Q

One vaporization/condensation cycle corresponds to a

A

theoretical plate

70
Q

In this experiment, you are using a solution of azulene in hexanes of known concentration. What weight of azulene, in milligrams, would you be using if you were starting with 1.5 mL of solution? Use 3 significant figures.

A

Your azulene solution has a concentration of 7 mg/mL

1.5 mL x 7 mg/mL = 10.5 mg

71
Q

Trifluoroacetic anhydride is a liquid. What volume, in milliliters, would you need to measure to obtain a 1 g sample of trifluoroacetic anhydride? Use 2 decimal places.

A

The density of trifluoroacetic anhydride is 1.511 g/mL.

volume = 1 g / 1.511 g/mL = 0.66 mL

72
Q

You have a mixture of your EAS starting material (azulene) and your product (trifluoroacetyl azulene) that you want to analyze by TLC. Which of the two compounds would have the lowest RF?

A

Trifluoroacyl azulene product

73
Q

Match the following items to their correct waste stream

  • leftover eluent
  • Solution of azulene starting material
  • Solution of red trifluoroacetyl azulene from the column
  • A used silica gel column in a glass pipette
  • Used TLCs
  • Water phase removed from your vial
A
  • leftover eluent -> nonhalogenated
  • Solution of azulene starting material -> Non-halogenated organic waste
  • Solution of red trifluoroacetyl azulene from the column -> Non-halogenated organic waste
  • A used silica gel column in a glass pipette -> glass waste
  • Used TLCs -> trash
  • Water phase removed from your vial -> aqueous waste
74
Q

In what region(s) of the NMR spectrum do you expect peaks for trifluoroacetyl azulene?

A

6.5-8.5 ppm

75
Q

In what region(s) of the NMR spectrum do you expect peaks for trifluoroacetyl azulene?

A

6.5-8.5 ppm

76
Q

If you were to take an IR spectrum of your trifluoroacetyl azulene product, in what region(s) of the spectrum do you expect to see relevant peaks?

A

1700 cm-1

Ochem Lab - CHE 3238 (1 decks)

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