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Chem 203 > Lab Final > Flashcards

Lab Final Flashcards

1
Q

2 methods to determine organic versus aqueous layer in solution

A
  1. add a drop of water. If water mixes with top layer, it is aqueous. If water falls to bottom layer, bottom layer is aqueous
  2. predict based on density. If organic solvent contains heavy atoms, like Cl, it will be on bottom. If organic solvent isnt heavy (like hexane or ethers), it will be on top
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2
Q

Acetic acid

A

just a general carboxylic acid

CH3COOH

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3
Q

What does the separatory funnel allow chemists to do?

A

Easily see the barrier between two layers and then seperate them using a stopcock

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4
Q

What does a liquid-liquid extraction require?

A

Two liquids that are immiscible (like oil and water)

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5
Q

What layer do charged compounds or ionic compounds go in?

A

“Like” layer

Often charged molecules are polar so they go in polar aqueous layer

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6
Q

What layer do uncharged organic compounds or non-ionic compounds go in?

A

Typically non-polar so they go in organic layer

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7
Q

How does extraction work?

A

Add an organic solvent and mix, then the desired compound (in our case dye) will move to aqueous or organic layer, then can use the separatory funnel to separate one layer from the other and isolate the desired compound

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8
Q

What is important when picking a solvent for extraction?

A

1) Will dissolve the solute of interest

2) Is immiscible to the aqueous layer (often water)

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9
Q

How should the separatory funnel be supported?

A

With a ring stand NOT a clamp

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10
Q

What must you do prior to separating the layer?

A

Extract the gas from the funnel

and then remove the stopper from the top of the funnel

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11
Q

Difference between washing and extraction?

A

Extraction moves the desired compound by placing it in the organic solvent

Washing keeps the desired compound in the starting layer

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12
Q

Partition coefficient

A

The ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium

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13
Q

Partition coefficient equation

A

P= (solubility of compound in organic layer)/(solubility of compound in aqueous layer)

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14
Q

What can you use to determine how many grams of desired compound is removed by the organic layer/aqueous?

A

System of equations and partition coefficient

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15
Q

Caffeine is wildly soluble in ethanol. Could you have used ethanol in- stead of dichloromethane to extract the caffeine from tea? Why or why not?

A

No

Ethanol is soluble in water and you would not be able to have two distinct layers to separate

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16
Q

What does TLC stand for?

A

Thin layer chromatography

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17
Q

What are some uses of TLC?

A

to see if a reaction has gone to completion

help identify final product

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18
Q

What do you need in order to be able to use TLC as an identification tool?

A

A known TLC of the sample to compare

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19
Q

How fast do polar substances elute in tlc?

A

Polar substances are more strongly attracted to the stationary phase (silica gel) and therefore elute more slowly

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20
Q

How fast do non-polar substances elute in tlc?

A

Non-polar or less polar substances are less attracted to the stationary phase (silica gel) and therefore elute more rapidly

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21
Q

Why use TLC compared to other methods of anaylsis?

A

low cost, quick analysis time, convient, and simple

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22
Q

How should you prepare the compound for analysis in TLC?

A

Dilute solution

Solvent should dissolve the compound well and evaporate quickly

Often use dichloromethane

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23
Q

How does the solvent move up plate in TLC?

A

capillary action

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24
Q

Solvent front

A

How far the solvent traveled in TLC

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25
Q

Retention factor

A

Rf= (distance traveled by compound)/(distance traveled by solvent front)

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26
Q

What is an advantage to 1-pot synthesis?

A

do not need to isolate intermediates at each step

can mix altogether

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27
Q

What is a disadvantage to 1-pot synthesis?

A

you can have more impurities in your final solution

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28
Q

How can you tell if 1-pot synthesis is working?

A

Color changes throughout the experiment is one way

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29
Q

What are the three compounds present in TLC?

A

1) Stationary phase
2) Mobile phase (the solvent)
3) The analyte (what you are studying)

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30
Q

What does it mean if you have multiple spots in same TLC channel/lane?

A

there are impurities in the analyte

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31
Q

Does the solvent need to dry before analyzing under UV light?

A

yes

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32
Q

Reflux definition

A

Heating a reaction flask to the boiling point of the solvent and recovering the solvent via condensation

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33
Q

What is an advantage of reflux over just heating?

A

Can heat at higher temperatures without the loss of solvent

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34
Q

When a water cooler condenser is used where should water enter and exit?

A

Water should enter at the lowest point

Water should exit at the highest point

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35
Q

When a water-cooled condenser is used why is it important for the water to enter the condenser at the lowest point and exit at the highest point?

A

Gravity ensures that the entire inner jacket is covered in cold water for maximum cooling

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36
Q

After performing a TLC on an unknown material, using dichloromethane as a developing solvent, you visualize one spot having an Rf of 0.05. In order to obtain information that is more useful would you use hexane or ethyl acetate as the developing solvent in your next trial? Include a brief explanation for your choice.

A

Ethyl acetate

The analyte did not elute very far in dichloromethane (less polar than ethyl acetate) and stuck to the polar stationary phase

Therefore, I would use a more polar developing solvent, ethyl acetate, in order to pick up the analyte and carry it further

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37
Q

How to determine which compound will have the greatest Rf value with same developing solvent?

A

Identify the least polar molecule (often the one that does not have hydrogen bonding abilities)

This least polar molecule will travel the furthest because it is not attracted to the stationary phase

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38
Q

What happens to the number of peaks in IR as the number of atoms in a molecule increases?

A

The number of peaks increase

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39
Q

What does NMR stand for?

A

nuclear magnetic resonance

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40
Q

What must happen during a vibration to be IR active?

A

change in dipole moment

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41
Q

How many vibrations are seen in IR for nonlinear molecules?

A

3n - 6

n= number of atoms

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42
Q

How many vibrations are seen in IR for linear molecules?

A

3n -5

n=number of atoms

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43
Q

Relationship between wavelength and energy?

A

longer wavelength, lower energy

if take the inverse of wavelength, then bigger number, higher energy

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44
Q

What is the relationship between bond strength and frequency in IR?

A

stronger bonds require more energy to vibrate

higher energy means higher frequency (since using inverse)

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45
Q

Where is the fingerprint region in IR?

A

400-1500 cm-1

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46
Q

What do degrees of unsaturation tell us?

A

number of double bonds, triple bonds, or rings

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47
Q

When to use degrees of unsaturation?

A

Both NMR and IR analysis

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48
Q

What type of energy is used for IR to cause vibration?

A

Infrared

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49
Q

What type of energy is used for NMR to cause nuclear spin?

A

Radiofrequencies

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50
Q

Where IR is concerned with the change in vibration, NMR is concerned with the change in … ?

A

direction of spin orientation

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51
Q

How does NMR work?

A

Looks at the amount of energy needed to flip the direction of spin orientation

Different nuclei environments will increase or decrease the amount of energy that is required to flip the nuclei spin

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52
Q

How does shielding affect amount of energy needed in NMR?

A

if a nuclei experiences shielding from nearby nuclei in its nuclear environment, it will require more energy to flip the nuclei spin

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53
Q

Chemical shift

A

a measure to the degree of which a nucleus in a molecule is shielded

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54
Q

Downfield in 1H NMR

A

to the left

indicates less shielding

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55
Q

Upfield in 1H NMR

A

to the right

indicates increased shielding

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56
Q

What do electronegative species do in 1H NMR?

A

electronegative species pull some electron density away

this leads to decreased shielding

decreased shielding leads to a downfield (left) shift in NMR

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57
Q

Shielding of sp2 carbons versus sp3 carbons

A

sp2 carbons experience less shielding and are shifted downfield

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58
Q

4 types of information contained in NMR spectra

A

1) Number of signals
2) Location of signals (chemical shifts)
3) Intensity (area under curve: integration)
4) Splitting pattern (multiplicity)

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59
Q

What do the number of signals in NMR correspond to?

A

the number of unique species environments

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60
Q

What is integration proportional to?

A

Area under the curve is proportional to the number of groups causing the peak

For example: integration of 2 means that 2 chemically equivalent groups are causing the peak

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61
Q

What is important to note with regards to integration?

A

Integration gives a ratio…sometimes have to multiply/divide to find the exact number

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62
Q

What does splitting pattern/multiplicy tell us?

A

the number of nonequivalent proton groups that are causing the shift

always one more peak is shown than number of groups (N+1 rule)

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63
Q

What do two splits (a doublet) in 1H NMR tell us?

A

there is 1 neighboring hydrogen group that is causing the shift

N+1 RULE: 1 neighboring group = 2 splits

64
Q

What do triplets in 1H NMR tell us?

A

there are 2 neighboring hydrogen groups that are causing the shift

N+1 RULE: 2 neighboring groups = 3 splits

65
Q

Can you observe multiplicity in 13C NMR? Why not?

A

Normally no

13C is so low in natural abundance that it is unlikely that neighboring 13C carbons caused splitting

Too much noise for accurate read

66
Q

Methods to separate two liquids

A

1) Liquid-liquid extraction

2) Distillation (simple or fractional)

67
Q

What is a method to obtain a dilute ethanol solution?

A

Ferment an aqueous solution of sucrose with yeast to produce ethanol

68
Q

What does a fermentation lock do?

A

Allows for CO2 gas to escape, but no oxygen to enter the system

69
Q

What should never happen in a distillation?

A

The distillation flask should never distill to dryness

70
Q

What is the first step in distillation?

A

clamp the boiling flask in place

the boiling flask serves as the anchor for the rest of your assembly

71
Q

Boiling definition

A

When the vapor pressure over the solution (atmospheric pressure) equals the vapor pressure of the solution

72
Q

Ideal gas law equation

A

PV = nRT

where R is the universal gas constant

73
Q

General gas equation

A

P1V1/n1T1 = P2V2/n2T2

74
Q

Relationship between total pressure and one of the gases in the mixture

A

Pa/Ptotal = Xa

where X is the mole fraction or composition of the vapor

75
Q

Plate

A

each evaporation/condensation sequence in distillation

76
Q

Fractional versus simple distillation

A

Fractional distillation has multiple plates in the condensing column

77
Q

What technique is most commonly used to purify liquids?

A

Distillation

78
Q

Distillation process

A

Heating a liquid to vaporize it, and then condensing the vapor back into the liquid state, and collecting that liquid into another container

79
Q

When is simple distillation useful?

A

When separating a liquid and solid or when two liquids have very different boiling points

80
Q

When is fractional distillation used?

A

When the boiling point difference is small

81
Q

What happens as you continue to perform fractional distillation?

A

the sample becomes purer

82
Q

Azeotrophic mixtures

A

a mixture of liquids that has a constant boiling point because the vapour has the same composition as the liquid mixture

83
Q

How to get proof from concentration by weight of alcohol?

A

multiply by 2

84
Q

How to get proof from concentration by weight of alcohol?

A

multiply by 2

85
Q

The boiling temperature of an ideal mixture of two liquids increases as distillation proceeds. Explain why

A

As the liquid with the lower boiling point evaporates off, you are left with a liquid with a higher boiling point

Therefore, as the reaction procedes you are left with a solution with a higher boiling point

86
Q

How do you calculate the actual yield of ethanol from a distillation?

A

1) Calculate density of a fraction
2) Calculate % composition of ethanol from chart
3) Calculate mass of alcohol in sample by multiplying percent ethanol by mass of sample
* repeat this for each individual fraction and then add at the END for actual yield in grams

87
Q

How to find the percent of ethanol in starting sample?

A

take the grams of ethanol that was distilled and divide by the total mass of the starting sample

(this assumes that you do not take into consideration the azeotrophic property of ethanol)

88
Q

What is the relationship between temperature and volume of the distillate?

A

As volume of the distillate increases, temperature of the distillate increases until it plateaus

The plateau occurs at the boiling point of water when ethanol is no longer being distilled

89
Q

How to determine the temperature of the first drops of distillate that will be observed when a mixture is subject to multiple distillate

A

Go to the boiling point of the liquid that corresponds to the vapor temperature of the first distilation (basically across once and down)

90
Q

What was the point of the DMAP + CH3I lab?

A

to determine which pathway was favored for an SN2 reaction that could have attacked either nitrogen on DMAP

91
Q

What does red indicate on an electrostatic potential map?

A

Areas that are high in electronegativity (more likely to act as nucleophile)

92
Q

What does blue indicate on an electrostatic potential map?

A

Areas that are low in electronegativity (less likely to act as an nucleophile)

93
Q

When is gravity filtration used?

A

the filtrate is the material of interest and we are removing a solid impurity

94
Q

Gravity filtration

A

Uses funnel paper and cone

95
Q

When is vacuum filtration used?

A

when the solid is the material of interest and we are removing a “liquid impurity”

96
Q

Pasteur pipe

A

cotton in the end of a small pipette

used for small volumes <15mL

would be used for gravity filtration instead of the funnel paper

97
Q

What type of funnel did we mostly use with vacuum filtration?

A

Buchner funnel

*square-looking top

98
Q

Hirsch funnel

A

has a more typical funnel look than a Buchner

smaller and sometimes we used it for vacuum filtration

99
Q

Bumping

A

When organic liquids are super-heated in a glass container, they have a tendency to boil in a violent fashion

To avoid bumping you can add boiling stones or a magnetic stir bar or constantly swirl the organic liquid while it is being heated

100
Q

Crystal field theory (CFT)

A

the bonding in coordination compounds is the result of electrostatic interactions and considers the effects of ligand charges on the energies of the metal d-orbitals

101
Q

Coordination complexes

A

salts containing a complex ion and counter ions

102
Q

What are the charged metal centers in coordination complexes seen as in CFT?

A

Lewis acids

103
Q

What are ligands in coordination complexes seen as in CFT?

A

Lewis bases

104
Q

Δo

A

crystal field splitting

the difference in energy between split d-orbitals

105
Q

What does a large Δo indicate?

A

The orbitals are too high in energy to move electrons up to the higher level…electrons must be paired first

106
Q

What types of ligands produce a large Δo?

A

Strong field ligands (will see paired electrons)

107
Q

What does a small Δo indicate?

A

The orbitals are low enough in energy to move electrons up to higher level before pairing them (referred to as a high spin complex)

108
Q

What types of ligands produce a small Δo?

A

Weak field ligands (will see unpaired electrons)

109
Q

Which color solution represents the highest energy and the strongest field ligands?

A

Yellow

Because it’s complement is purple which is closest color to high energy UV region

Has a shorter wavelength and larger Δo

110
Q

Which color solution represents the lowest energy and the weakest field ligands?

A

Green

Because its complement is red which is closest color to low energy Infrared region

Has a longer wavelength and smaller Δo

111
Q

Which type of coordination complexes were we concerned with?

A

Transition metals

112
Q

Coordination number

A

The number of ligand atoms that are bonded directly to the central metal ion

113
Q

Are ligands normally negatively charged or positively charged?

A

negatively charged

or neutral!

114
Q

Rules for writing formulas of coordination compounds

A

1) Cation is written before the anion
2) Charge of cation is balanced by charge of anion
3) For anion: metal listed first, then neutral ligands, then anionic ligands and entire formula in brackets

115
Q

Rules for naming coordination compounds

A

1) the cation is named before the anion
2) within complex ion: ligands are alphabetically named before the metal
3) Anionic ligands drop the -ide suffix and add -o
4) a numerical prefix is used to indicate the number of ligands
5) oxidation state of central metal ion needs to be placed in brackets with roman numerals
6) if the complex ion is an anion: drop the ending of the metal name and add -ate

116
Q

How to write water when naming coordination compounds?

A

aqua

117
Q

What not to forget when naming coordination compounds

A

list ligands alphabetically

cation before anion

if complex ion is an anion, at -ate to metal

always put metals oxidation state is parentheses

118
Q

How to write NH3 when naming coordination compounds?

A

ammine

119
Q

What is E when using Ts diagrams?

A

E is the smaller wavelength max (found experimentally)

120
Q

How to name CO in coordination compounds?

A

carbonyl

121
Q

C2O4

A

oxalate

122
Q

Three steps of catalytic cycle for suzuki reaction

A

1) Oxidative addition (catalyst inserts into alkyl halide)
2) Transmetallation (catalyst binds two rings together)
3) Reductive elimination (catalyst leaves and rings are bound)

123
Q

Does suzuki coupling happen in absence of a base?

A

no

we used base KOH

124
Q

What are two competing factors of biphenyl’s dihedral angle?

A

sterics and p-conjugation

if too substituted, sterics win out and a 90º dihedral angle is observed

125
Q

What is the relationship between BDE and bond length?

A

Negative relationship

As BDE increases, bond length decreases

126
Q

Why must cyclopentadiene be kept on ice and be added to a cold solution?

A

It can dimerize to form dicyclopentadiene which will not react in this Diels-Alder reaction

127
Q

Three steps of catalytic cycle for suzuki reaction

A

1) Oxidative addition (catalyst inserts into alkyl halide)
2) Transmetallation (catalyst binds two rings together)
3) Reductive elimination (catalyst leaves and rings are bound)

128
Q

Vicinal relationship of protons

A

protons are separated by three bonds

129
Q

When are geminal hydrogens not chemically equivalent?

A

if the protons of interest are not free to exchange and are situated above a double bond system

like the hydrogens at the top of bridge in Diels-Alder product

130
Q

What is the relationship between BDE and bond length?

A

Negative relationship

As BDE increases, bond length decreases

131
Q

Why must cyclopentadiene be kept on ice and be added to a cold solution?

A

It can dimerize to form dicyclopentadiene which will not react in this Diels-Alder reaction

132
Q

Geminal relationship of protons

A

protons are separated by two bonds

133
Q

Vicinal relationship of protons

A

protons are separated by three bonds

134
Q

When are geminal hydrogens not chemically equivalent?

A

if the protons of interest are not free to exchange and are situated above a double bond system

like the hydrogens at the top of bridge in Diels-Alder product

135
Q

Concerted

A

a single step chemical reaction

all bonds are broken and formed at the same time

136
Q

Diene

A

molecule that has two carbon-carbon double bonds

137
Q

Pericyclic

A

bonds are broken and formed with a concerted, cyclic transition state

138
Q

Chemiluminescence

A

occurs when chemical reactions excite a molecule (increase its energy) and then the excited molecule loses its energy through photons, which create observable light called Chemiluminescence

139
Q

How is luminol used in forensics?

A

tests for the prescence of blood

140
Q

What is a common oxidizing agent?

A

hydrogen peroxide

141
Q

How does luminol work?

A

Luminol is mixed in solution with an oxidizing agent (H2O2) and base

and then the iron in hemoglobin acts a catalyst for chemilluminescence reaction to take place

142
Q

Synthesis of luminol steps

A

1) High heat

2) Reflux in base to perform reduction reaction

143
Q

What did we quench with a lot?

A

acetic acid

CH3COOH

144
Q

What did we use a solvent a lot?

A

dichloromethane CH2Cl2

145
Q

Common drying agents

A

magnesium sulfate

MgSO4

146
Q

Why is recrystallization used?

A

it purifies an impure compound in a solvent

147
Q

How does recrystallization work?

A

an impure compound which is dissolved in a solution is heated to high temperatures

the solution is then cooled and the desired substance crystallizes before the impurities

this leaves the impurities behind once filtered and makes the solution purer

148
Q

Main steps of recrystallization

A

1) Dissolve the solute in solvent by heating
2) Hot gravity filtration (if needed)
3) Vacuum filtration
4) Drying the crystalls

149
Q

What does a drying agent do?

A

Reacts with water and allows us to filter out the water through filtration

Often there is clumping when water is absorbed by MgSO4

150
Q

What is melting point used for?

A

1) Determining identity of a substance

2) Determining the purity of a substance

151
Q

How is melting point recorded?

A

As a RANGE of temperatures

152
Q

How does melting point indicate purity?

A

Higher melting temperatures mean more pure

Narrower range of melting point means more pure

153
Q

Paramagnetic

A

unpaired electrons in valence shell

154
Q

What must you consider when calculatin Rf value?

A

the starting “line” of solvent

155
Q

Acetone

A

CH3 (carbonyl) CH3

basic ketone

156
Q

What would happen if your solvent level is above the level of initial spots on Rf plate?

A

sample would wash down

157
Q

Chemical formula for sucrose

A

C12H22O11

Chem 203 (7 decks)

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