Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A level Chemistry > Unit 4.8 - Organic synthesis and Analysis > Flashcards

Unit 4.8 - Organic synthesis and Analysis Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What type of reactions do double bond reactions tend to be?

A

Addition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How are addition polymers produced?

A

From alkenes, where the double bond id broken to form a repeating unit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe a polymer repeating unit

A

No double bond
Saturated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How should a repeating unit always be shown?

A

With extended bonds through the brackets showing that it bonds to other repeating units on both sides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

When do condensation polymers form?

A

When a water molecule is removed from the species of a reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How are polyesters formed?

A

In a reaction between dicarboxylic acids and a diol (a dialcohol), producing an ester linkage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Type of linkage in a polyester

A

Ester

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Common example of a polyester

A

Terylene, known as PET

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is Ethan-1, 2-diol present in?

A

Antifreeze

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is given off when a dicarboxylic acid and a diol produce an ester linkage in a polyester?

A

Water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what else can you also make an ester linkage with with an alcohol?

A

a dioyl chloride

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

another word for ethan-1,2 - diol

A

ethylene glycol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what would be eliminated in the reaction between a carboxylic acid and an acid chloride?

A

HCl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How are polyamides formed?

A

In a reaction between a dicarboxylic acid (or a diol chloride) and a diamine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the removed during the reaction to form polyamides?

A

A molecule of water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is left when a molecule of water is removed during a reaction between a dicarboxylic acid (or a dioyl chloride) and a diamine?

A

An amide linkage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Common examples of polyamides

A

Nylon - 6,6 and Kevlar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Explain all of the differences between addition polymerisation and condensation polymerisation

A

If the monomer is an alkene, then addition polymerisation occurs
No small molecule is lost and the polymer is the only product, then addition polymerisation has occurred
If a small molecule e.g - H2Oor HCl is produced along side side the polymer then a condensation polymerisation has taken place
The monomer(s) contain function groups such as -NH2, -COOH, -OH or -COCl then condensation polymerisation occurs
The chain contains the amide link -C(O)N(H) or an ester linkage -OC(O)- then condensation polymerisation has occurred
The chain only consists of carbon atoms then addition polymerisation has occurred

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Properties of addition polymerisation

A

The monomer is an alkene
No small molecule is lost
The chain only consists of carbon atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Properties of condensation polymerisation

A

A small molecule e.g - H2O or HCl is produced
The monomer(s) contain functional groups such as -NH2, -COOH, -OH, -COCl
The chain contains an amide link -C(O)N(H) or an ester linkage -OC(O)-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Why are many of the reaction in organic chemistry laborious?

A

Since when you react two organic reagents you will produce some undesired products

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Impurities

A

Undesired products

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Name for undesired products

A

Impurities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What will there also be when trying to form something in a reaction except for the usual impurities?

A

Unreacted starting materials in the mixture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Purification

A

For a pure sample, we need to separate the product from the mixture

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Separating the product from the mixture for a pure sample

A

Purification

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Why do many organic reactions not go to completion as required?

A

Other products may be produced, and some unreacted starting product may remain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What’s an important part of any organic preparation?

A

The separation and purification of the products

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What will you also have in the reaction products when producing ethyl ethanoate?

A

Ethanol and ethanoic acid that’s unreacted and some water that also forms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Miscible liquids

A

Will mix and dissolve in each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Liquids that will mix and dissolve in each other

A

Miscible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What’s important to note about the solution produced when making ethyl ethanoate?

A

All of the four compounds present are miscible with each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What would we see when making ethyl ethanoate and why?

A

A colourless liquid
All four compounds are miscible with each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What conditions could the products be in depending on the reaction?

A

Could be an insoluble solid, may be present in solution or as immiscible liquids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What does each mixtures of products after an organic reaction need?

A

A different method of separation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

When can distillation be used to separate the products from the other substances present in the reaction mixture?

A

If the product does not decompose at or below its boiling temperature and the boiling temperature is not too high

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What separation technique can we use If the product does not decompose at or below its boiling temperature and the boiling temperature is not too high ?

A

Distilllation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

When can simple distillation be used to separate a product from the other substances present in the reaction mixture?

A

If the boiling temperature of the product differs by a reasonable amount (perhaps 20 degrees Celsius or more) from the boiling temperatures of the other compounds present

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

What can simple distillation also be used for?

A

Separating a volatile liquid from other substances in the mixture that are not volatile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What is used to separate a volatile liquid from other substances in the mixture that are not volatile?

A

Simple distillation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What separation technique can be used if the boiling temperature of the product differs by a reasonable amount?

A

Simple distillation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Example of simple distillation

A

The distillation of 2-chloro-2-methyl propane from its mixture with 2-methylpropan-2-oil and hydrochloric acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

When is fractional distillation used?

A

If the boiling temperatures are closer together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What is used to separate if boiling temperatures are closer together?

A

Fractional distillation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What is used during fractional distillation and why?

A

A fractionating column, which enables more efficient separation of the products to occur

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

Give 2 examples of using fractional distillation

A

-the separation of ethanol obtained from the fermentation of sugars is more effective if fractional distilllation is used
-the primary separation of the products present in crude oil (petroleum) is also carried out by fractional distillation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What reaction technique is used to separate compounds that decompose just before or at their boiling temperatures or have very high boiling tempatures?

A

Distillation is carried out under reduced pressures (vacuum distillation) or steam distillation can be used

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

When is distillation carried out under reduced pressures (vacuum distillation) or is steam distillation used?

A

For compounds that decompose just before or at their boiling temperatures or have very high boiling temperatures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What does pressure do to the boiling point of a compound?

A

The lower the pressure, the lower the boiling point of a compound

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

What is vacuum distillation?

A

When there’re less pressure exerted on the vapour since this decreases the compounds boiling temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Give an example of reduced pressure distillation working

A

The alkane dodecane C12H26 boils at 216 degrees under atmospheric pressure (101kpa) but at 92 degrees if the pressure is reduced to 1.3kpa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What do we need to work out when working with miscible liquids?

A

Which is the organic layer and which is the aqueous layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

Which layer is discarded and which layer is kept with miscible liquids?

A

Discard the aqueous layer
Keep the organic layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

What are the 2 methods of determining what out organic layer and what our aqueous layer is when working with miscible liquids?

A

Use density data
Keep adding deionised water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

How do we use density data to work out which layer is an organic layer with miscible liquids?

A

The lower density one will be on top

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

Explain properly how we would use deionised water to see which layer is an organic layer with miscible liquids

A

Keep adding deionised water to see which layer grows
There will still be water present in the organic product, which is what we keep
In order to get a dry product (dry = no water) we should add a drying agent for example calcium chloride or magnesium sulphate, which are hygroscopic (absorb moisture)
We could then use this in fractional distillation and compare its boiling point with literature values to know that its been purified well

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Drying agents \examples

A

Calcium chloride
Magnesium sulphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

Why are calcium chloride and magnesium sulphate examples of drying agents?

A

They’re hygroscopic (absorb moisture)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

How can we tell if something has been purified well?

A

Use it in fractional distillation and compare its boiling point with literature values

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

Example of organic products that are sensitive to heat

A

Esters

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

What do some organic products do upon excessive heating and why?

A

Decompose
They’re sensitive to heat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

Which separation technique do we use if organic products are sensitive to heat and decompose upon excessive heating?

A

Steam distillation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

When do we use steam distillation?

A

When organic products are sensitive to heat and may decompose upon excessive heating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

Which industry is steam distillation very important n?

A

The perfumery industry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

Why is steam distillation so important in the perfumery industry?

A

Essential oils extracted from plants may decompose if heated to their boiling temperatures at atmospheric pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

How does steam distillation work?

A

Steam is passed into the reaction mixture and the volatile compounds present pass over with steam, and condense in the receiving flask

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

What is one of the most widely used oils in the perfume industry? Explain how it is used

A

Rose oil
Steam distillation of rose oil gives an oil (containing a number of different compounds) and water from the condensed vapours

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

What do we look at during solvent extraction?

A

The solubility of a product in different solvents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

What is solvent extraction?

A

A method that depends on the differing solubility of a compound in two immiscible solvents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

Give an example of a differing solubility of a compound in different immiscible solvents

A

Iodine is about 90x more soluble in tetrachloromethane than in water

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

What happens if tetrachloromethane is added to an aqueous solution of iodine and the mixture shaken?

A

Most of the iodine is extracted into the tetrachloromethane layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

How do we separate 2 layers?

A

Using a separating funnel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
73
Q

What do we need to do if CO2 gas forms in a reaction that requires the use of a separating funnel?

A

Make sure to release pressure in the funnel periodically

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
74
Q

What is used to separate a solid from a liquid?

A

Filtration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
75
Q

What is filtration used for?

A

Separating a solid and a liquid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
76
Q

How can filtration be carried out?

A

Using a filter paper and a funnel or sometimes with a plug of cotton wool to stop the solid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
77
Q

The use of what makes filtration quicker and why?

A

The use of fluted filter paper
The filtrate only needs to travel through one layer of filter paper and the paper only touches the funnel at the folds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
78
Q

What is fluted filter paper used for?

A

Making filtration faster

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
79
Q

What’s another thing we can use for filtration?

A

Filtration using a Büchner funnel (vacuum filtration)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
80
Q

What needs to be done once the solid is in the funnel after filtration?

A

It needs to be washed with an appropriate solvent and dried in the air, or in a drying oven at a temperature below its melting temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
81
Q

When are the products obtained by crystallisation?

A

If the solid is present as a solute in solution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
82
Q

How are the products obtained if the solid is present as a solute in solution?

A

By crystallisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
83
Q

Why would a solution be coloured when it’s supposed to be colourless?

A

Due to the presence of impurities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
84
Q

Why would a solution be coloured when it’s supposed to be colourless?

A

Due to the presence of impurities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
85
Q

What is used when a solution is coloured when it’s supposed to be colourless?

A

Decolourising charcoal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
86
Q

What does declourising charcoal do?

A

Absorbs the coloured impurities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
87
Q

How is decolourising charcoal used?

A

The solution is boiled with a little decolourisng charcoal to remove the colour and then filtered hot to remove the charcoal that contains the absorbed colour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
88
Q

What do we do after using decolorising charcoal?

A

The solution is filtered hot to remove the charcoal that contains the absorbed colour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
89
Q

How is a filtrate concentrated?

A

By boiling and is then cooled

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
90
Q

How Dow e know that a solution has been sufficiently concentrated?

A

Crystals of the solute appear on cooling. These are filtered off and dried.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
91
Q

What does it mean if crystals of a solute appear on cooling?

A

The solution has been sufficiently concentrated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
92
Q

What is done to crystals of a solute?

A

They’re filtered off and dried

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
93
Q

What does it mean mean if no crystals appear on cooling?

A

Then the solution needs to be made more concentrated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
94
Q

How do we know that a solution needs to be made more concentrated?

A

If no crystals appear on cooling

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
95
Q

What type of solvent do we need to choose when extracting soluble solids from solution?

A

Where the solid dissolves poorly when cold but well when hot

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
96
Q

When does extra care need to e taken when concentrating a solution?

A

If the solvent is flammable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
97
Q

What is used when concentrating a solution if the solvent is flammable?

A

Generally a water bath or some method of electrical heating, for example a hot plate is used

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
98
Q

When would a solute need to be recrystallised?

A

When the solute obtained by crystallisation may not be pure

99
Q

Essential steps for recrystallisation

A
  1. Dissolve impure solid in minimum amount of hot solvent
  2. If solid remains, filter this off whilst hot (hot filtration - place apparatus in oven or water bath)
  3. Allow solution to cool for crystals to form
  4. Filter crystals, was with cold solvent, dry
  5. Record melting temperature of solid and compare with literature values
100
Q

Name 2 ways of measuring impurity

A

Comparing melting temperature to literature values
Use chromatography

101
Q

Explain exactly how we would use melting temperatures as a way of measuring impurity

A

Impure —> melting temperature will be lower than its pure form and melts over a range of temperatures
Pure —> sharp melting temperature (1-2 degrees deviation from literature value)

102
Q

Explain the melting temperature of an impure compound

A

Melting temperature will be lower than its pure form and melts over a range of temperatures

103
Q

Explain the melting temperature of a pure compound

A

Sharp melting temperature (1-2 degrees deviation from literature value)

104
Q

Empirical formula

A

Simplest whole number ratio of atoms

105
Q

What is chromatography?

A

An analytical technique used to separate and identify component molecules in a mixture

106
Q

What are the stages of chromatography?

A

The mobile phase and the stationary phase

107
Q

The mobile phase of chromatography

A

A substance that allows molecules to move over or through the stationary phase

108
Q

What can the mobile phase be n the form of?

A

A liquid or a gas, depending on the type of chromatography being carried out

109
Q

What move further in the mobile phase?

A

More soluble products

110
Q

The stationary phase

A

A substance that has affinity to molecules in the mixture being analysed

111
Q

Relationship between the affinity of a molecule in the stationary phase and the distance it moves in the mobile phase

A

The greater the affinity of a molecule to the stationary phase, the shorter the distance it moves with the mobile phase

112
Q

What’s the mobile and what’s the stationary phase in paper chromatography?

A

Mobile phase —> solvent you dip the paper in
Stationary phase —> the chromatography paper

113
Q

What happens during paper chromatography for a more soluble product?

A

Moves further up the chromatography paaper

114
Q

What type of products move further up the chromatography paper?

A

More soluble ones

115
Q

what happens to less soluble product during paper chromatography?

A

Stick to the paper

116
Q

What type of products stick to the paper during paper chromatography?

A

Less soluble ones

117
Q

What does every component molecule in a mixture used in chromatography have?

A

A unique Rf value in a particular solvent mixture

118
Q

What ones each molecule in a mixture have a unique Rf value for?

A

Particular solvent mixture

119
Q

How is an Rf value calculated?

A

By comparing the distance moved by the mobile phase and the molecule

120
Q

Equation for working our Rf

A

Distance moved by the molecule/distance moved by solvent

121
Q

What is chromatography a technique used for?

A

To separate substances from a mixture by their slow movement, at different rates, through or over a stationary phase

122
Q

What has chromatography been developed to be able to do now?

A

So that mixtures of substances can be separated by using a number of different methods

123
Q

How do we know which chromatography method to use?

A

They’re appropriate to the number and nature of the components present

124
Q

How is chromatography now used in a quantitative way even though it as originally a qualitative method?

A

It’s often used in conjunction with mass spectrometry to identify individual components that are present in the mixture

125
Q

Why is chromatography often used in conjunction with mass spectrometry?

A

To identify individual components that are present in the mixture

126
Q

How is chromatography used in conjunction with mass spectrometry?

A

Chromatography separates the components. Inject the components through a mass spectrum = fragments it = can characterise the molecules

127
Q

2 mechanisms for the separation process during chromatography

A

Partition
Adsorption

128
Q

Which methods can be used to decide which dyes are present following chromatography?

A

Take IR spectrum and compare
Chromatography with a different solvent

129
Q

TLC

A

Thin layer chromatography

130
Q

What is the stationary phase in paper chromatography?

A

Water trapped in the cellulose fibres of the paper

131
Q

What is the stationary phase in TLC?

A

A layer of silica (SiO) or aluminium oxide (Alp) coated onto a plastic or glass plate

132
Q

What technique is similar to paper chromatography?

A

TLC

133
Q

Explain how paper chromatography/TLC is carried out

A

Spots of starting materials in a suitable solution are placed at the bottom of a piece of chromatography paper or the initial solvent level below the spots
The solvent front then rises up the paper/plate, separating the mixture into a series of spots
When the solvent front has risen to a suitable level, the paper/plate is removed and dried
The position of the separated spots and the solvent front are notes and the distance that these have risen from the starting line is measured

134
Q

What happens when the solvent front rise up the paper/plate during paper chromatography/TLC?

A

Rises up the paper, separating the mixture into a series of spots

135
Q

Where do we measure zero from during chromatography?

A

The pencil line

136
Q

Why do we draw our zero line with pencil during paper chromatography?

A

Since biro ink would be separated by the solvent

137
Q

When do we have a solvent front?

A

Once the solvent has gone past all the spots

138
Q

Where do we measure up to the spots during paper chromatography/TLC?

A

The centre of spots

139
Q

How do we work out where the centre of spots are during paper chromatography?

A

Highest-lowest point of spot/2

140
Q

What can we compare using paper chromatography?

A

The position of the spots for a known and unknown solute can be compared to see if they have travelled the same distance

141
Q

What can we calculate from paper chromatography/TLC?

A

The Rf value

142
Q

When is two-way separation used?

A

When the use of a particular solvent does not completely separate the spots

143
Q

What do we use when the use of a particular solvent does not completely separate the spots during chromatography?

A

Use two-way separation

144
Q

How is two-way separation done?

A

The dried chromatogram is rotated through 90 degrees and then a different solvent is used on it

145
Q

When is the identification of spots easy during chomatography?

A

When they’re coloured

146
Q

What is done when solutes produce colourless spots during chromatography ?

A

The chromatogram is sprayed with a suitable reagent that causes the spots to become coloured

147
Q

What would we do with a chromatogram containing colourless spots of different amino acids?

A

Spray it with a solution of ninhydrin
Gently warm the paper = blue-purple spots appear that show the position of the different amino acids

148
Q

What appear to show the positions of different amino acids following the addition of ninhydrin to a chromatogram?

A

Blue-purple spots

149
Q

What’s the name for the process by which TLC separates amino acids?

A

Adsorption

150
Q

Wha’s another method apart form spraying a chromatogram with ninhydrin that can be used to show the positions of colourless spots?

A

Shine UV light on the plate

151
Q

What will happen when shining UV light on a chromatogram?

A

If the separated compounds are fluorescent, they will show a colour

152
Q

Another way apart from a solution of ninhdyrin on the chromatogram and shining UV lights on the plate to see colourless spots

A

The plate itself can have a coating of fluorescent materials and then the plate is exposed to UV light. The spots then show up dark spots on a fluorescent background.

153
Q

advantages of TLC over paper chromatography

A

Faster
The thin layer on the plates can be made from a variety of materials
Important uses in forensic science

154
Q

What’s the most common type of gas chromatography?

A

Gas-liquid chromatography (GLC)

155
Q

What happens during gas-liquid chromatography?

A

A gaseous mixture is passed “through” liquids particles supported on an inert (Unreactive) solid

156
Q

GLC

A

Gas-liquid chromatography

157
Q

How is the gaseous mixture swept into the column for GLC?

A

By a carrier gas

158
Q

Carrier gases used in GLC

A

Hydrogen
Helium
Argon

159
Q

Why are hydrogen, helium or argon chosen as carrier gases in GLC?

A

The carrier gas must not react with any of the substances

160
Q

What does the column for GLC contain?

A

Fine solid material or is a hollow column whose walls are coated with a solid on which there is a liquid stationary phase

161
Q

What s used instead of Rf in GLC?

A

RT

162
Q

RT

A

Retention time

163
Q

Retention time (RT)

A

The time taken form the sample ending the injection point and passing through the chromatography column before reaching the detector

164
Q

The time taken form the sample ending the injection point and passing through the chromatography column before reaching the detector

A

Retention time (RT)

165
Q

What factors does the efficient separation of the compounds in a mixture depend on?

A

Volatility of the compound itself
The column temperature
The length of the column
The flow rate of the carrier gas

166
Q

What’s an important factor in separating compounds by GLC for similar compounds (e.g - those in the same homologous series)?

A

Their boiling temperatures

167
Q

What vary enormously because of, for example, the volatility of the compound, the column temperature, the length of the column and the flow rate of the carrier gas?

A

Retention times

168
Q

What does identification by retention time depend on?

A

The conditions being exactly the same

169
Q

What is often done to the separated compounds following gas chromatography and why?

A

They’re led into a mass spectrometer, where a positive identification can be made since retention times can vary enormously so its best not to just rely on these

170
Q

What can be done to compounds that have been led into a mass spectrometer following gas chromatography?

A

Positive identification can be made

171
Q

GC-MS

A

Gas chromatography, mass spectrometry

172
Q

What is the ABE fermentation process?

A

A method of bacterial fermentation that produces propanone (acetone), butan-1-ol and ethanol from starch

173
Q

Which compounds will come of the column first?

A

Lowest boiling point

174
Q

What does a faster retention time mean?

A

Comes off the column first

175
Q

What would a lower boiling point mean in terms of retention time?

A

Lower boiling point = lower retention time

176
Q

What does every substance have a unique one of?

A

A unique chromatogram

177
Q

What does the area under a peak on a chromatogram represent?

A

How much of a substance you have

178
Q

How do you work out how much of a substance you have from a chromatogram?

A

Use the area under the peak

179
Q

What do you do if you’re asked to work out the % of a specific substance from a chromatogram?

A

Area of that substance/total area of all peaks x 100

180
Q

What would be different if gas chromatography was carried out at a different temperature and why?

A

Relative peak areas would be different
Because it would be dependent on whether a substrate would decompose upon heating

181
Q

Why would the relative peak areas on a chromatogram be different if gas chromatography was carried out at a different temperature?

A

Because it would be dependent on whether a substrate would decompose upon heating

182
Q

HPLC

A

High performance liquid chromatography

183
Q

When is high performance liquid chromatography used and why?

A

For heat sensitive substances that vaporise at high temperatures
To avoid them evaporating or decomposing, we use solvents that the substance will dissolve in

184
Q

What do we use for heat sensitive substances that vaporise at high temperatures?

A

HPLC

185
Q

Explain how HPLC works

A

The column is packed with solid particles (of uniform size) and the mixture sample is dissolved in a suitable solvent
The solution is then forces through the column at high pressure

186
Q

What is the column packed with for HPLC?

A

Solid particles of uniform size

187
Q

Applications of HPLC

A

Testing urine samples of athletes for the presence of banned substances
In food chemistry - antioxidants are added to fatty food products such as margarine and cream cheese to help prevent oxidation

188
Q

What are added to fatty food products and why?

A

Antioxidants
To prevent oxidation

189
Q

Most common antioxidants

A

BHA
BHT
Various esters of Gallic acid

190
Q

Where can the C(CH3)3 group be found in the antioxidant BHA?

A

In the 2- or 5- positions in the ring

191
Q

Spectroscopy

A

The interaction between light (em radiation) and matter

192
Q

Spectroscopy techniques

A

Infra red (IR) spectroscopy
Nuclear magnetic resonance (NMR) spectroscopy
UV/Visible spectroscopy
Mass spectrometry (MS)

193
Q

How do we read a mass spectrum?

A

Furthest peak to the right = molecular ion peak = Mr of the compound
The other peaks represent the possible fragments of the molecular ion

194
Q

Which peak is the molecular ion peak on a mass spectrum?

A

The furthest peak to the right

195
Q

What does a mass spectrum always keep and what does it discard?

A

Positive ions (the fragments) are kept
Discards negatives and radicles

196
Q

How do we use IR spectroscopy?

A

Determine functional groups present using the data sheet

197
Q

What is IR spectroscopy used in and how?

A

Breathalysers (sensitive to C-O, which is only in alcohols)

198
Q

What makes an element nmr active?

A

An odd number of nucleons

199
Q

Give 2 elements that are nmr active and are used for NMR spectroscopy + explain

A

C-13 and protons
Odd number of nucleons

200
Q

What do the number of peaks on a carbon-13 nmr spectrum represent?

A

The number of carbon environments

201
Q

What do the number of peaks on the proton nmr represent?

A

The number of hydrogen environments

202
Q

What do we use the chemical shifts in NMR for?

A

Use the data sheet to identify types of carbon/proton

203
Q

When are chemical shifts generally greater?

A

If the carbon atoms are closer to EN toms, and also for carbon atoms close to alkene groups

204
Q

Why do we now see splitting patterns in the NMR spectra used?

A

Due to the high resolution used

205
Q

Why would NMR spectra now have a different number of peaks?

A

Due to splitting patterns forming

206
Q

Name for the little peaks seen around the big peaks in high resolution NMR spectra

A

Splitting patterns

207
Q

Splitting patterns

A

Little peaks seen around the big peaks in high resolution NMR spectra

208
Q

What do splitting patterns give us information about?

A

Neighbouring protons

209
Q

Explain how splitting patterns give us information about neighbouring porotons

A

If we have 5 close peaks, there’s 4 neighbouring protons for that carbon

210
Q

Name for the splitting pattern produced when n=0

A

Singlet

211
Q

Name for the splitting pattern produced when n=1

A

Doublet

212
Q

Name for the splitting pattern produced when n=7+?

A

Multiplet

213
Q

n+1 rule

A

The peaks split not one more than the number of hydrogens on the neighbouring carbon atom

214
Q

Are hydrogens bonded to Os seen as neighbouring hydrogens to a carbon atom? Explain

A

No - OHs are usually singlets

215
Q

How are integration factors found?

A

By the area under the peak

216
Q

Where are integration factors indicated?

A

Above the peak

217
Q

What do integration factors indicate?

A

The number of identical hydrogen atoms corresponding to that peak

218
Q

How can methylpropanal and butanone be distinguished even though they both give 3 peaks in their proton nmr spectra?

A

Because the integration factors of the peaks are different
Methylpropanal —> 6:1:1
Butanone —> 3:3:2

219
Q

What 2 things must we do to prepare a sample for nmr analysis?

A

Choose a suitable solvent
Choose a standard

220
Q

How do we choose a suitable solvent for nmr analysis?

A

Hydrogen atoms absorb radiation so its important to choose one that contains no hydrogen atoms

221
Q

Suitable solvents for nmr analysis

A

CCl4 and CDCl3

222
Q

Why must a standard be added for nmr analysis?

A

To calibrate the spectrum

223
Q

Standard normally used for nmr analysis

A

Tetrmethylsilane (TMS)

224
Q

Why is tetramethylsilane usually used as a standard for nmr analysis?

A

Produces a single, singlet peak which is very intense
Has highly shielded H atoms (=peak at a lower frequency than most organic molecules)
Is cheap and non-toxic

225
Q

What does it do on an nmr spectrum when a standard has highly shielded H atoms?

A

Peaks at a lower frequency than most organic molecules

226
Q

What happens to a TMS standard before an nmr spectrum is produced?

A

It’s usually erased

227
Q

Explain, in terms of the electromagnetic spectrum why something would appear colourless

A

Doesn’t absorb in the visible region

228
Q

How is distillation done?

A

Reduce the temperature of the mixture to below the lowest boiling temperature and let the mixture warm up slowly

229
Q

Why would compounds form in approximately equal amounts in a reaction?

A

Intermediate carbocations have similar stabilities

230
Q

How do we work out relative peak area on a 1H NMR spectrum?

A

It’s just however many hydrogen atoms are in each environment

231
Q

Explain why the molar percentage of each compound cannot be used to find the percentage by mass of each component if the relative molecular mass of each component differs on a gas chromatogram

A

If relative molecular masses are different, the number of moles present in the chromatogram is not directly related to the mass of each component

232
Q

Explain what happens to IR absorptions when going from one compound to another

A

Increase and decrease depending on the different bonds

233
Q

why would compounds containing Cl or Br have a number of molecular ion signals?

A

since they have different isotopes

234
Q

give examples of compounds that may have a number of molecular ion signals and explain

A

those containing Cl or Br
they have different isotopes

235
Q

What do we get reduce yields from during a reaction?

A

Incomplete extraction by solvent
Incomplete distillation/decomposition of product

236
Q

What do we need to remember to do when writing repeating units and reactants that form it and other products?

A

write n

237
Q

What do we do with relative peak area ratios on 1H NMR spectra?

A

Show the ratio of atoms in each region (not the literal number at H atoms in each region)

238
Q

What do we know is true when something undergoes “complete oxidation”?

A

That the products will add up to be the exact same length. (No minor products will make up for some of the atoms)

239
Q

What does 2 oxygen atoms in each module suggest when not a carboxylic acid?

A

An ester

240
Q

What do we use to safely heat?

A

An electrically heated water bath

241
Q

Why do we use a “minimum amount of hot solvent” during recrystallisation?

A

So that the maximum amount of product can crystallise out on cooling

242
Q

What does it mean if we can’t identify things from gas liquid chromatography?

A

Their retention times must be the same

243
Q

Do chemically equivalent protons show splitting? Explain

A

No, they only split when there’s something different next door

A level Chemistry (39 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions