4.2 Alcohols, haloalkanes and analysis Flashcards
1
Q
What is the general formula for alcohols?
A
C.H2n+1OH
2
Q
Why do alcohols have relatively low volatility?
A
Due to their ability to form hydrogen bonds between alcohol molecules.
3
Q
Which alcohols are soluble in water?
A
Smaller alcohols (up to 3 carbons) because they can form hydrogen bonds with water.
4
Q
How does the length of the hydrocarbon chain affect the solubility of alcohols?
A
The longer the hydrocarbon chain, the less soluble the alcohol.
5
Q
What is ethanol commonly used for?
A
As ‘alcohol’ in alcoholic drinks and as a solvent in the form of methylated spirits.
6
Q
What is methanol used for?
A
As a petrol additive to improve combustion and as a feedstock in the production of organic chemicals.
7
Q
Define primary alcohols.
A
Alcohols where 1 carbon is attached to the carbon adjoining the oxygen.
8
Q
Define secondary alcohols.
A
Alcohols where 2 carbons are attached to the carbon adjoining the oxygen.
9
Q
Define tertiary alcohols.
A
Alcohols where 3 carbons are attached to the carbon adjoining the oxygen.
10
Q
What occurs during the complete combustion of alcohols?
A
They burn with complete combustion producing CO2 and H2O.
11
Q
What is the combustion reaction for ethanol?
A
C2H5OH + 3O2 → 2CO2 + 3H2O
12
Q
What is the role of potassium dichromate in oxidation reactions of alcohols?
A
It is an oxidising agent that causes alcohols to oxidise
Potassium dichromate (K2Cr2O7) can oxidise primary, secondary, and tertiary alcohols depending on the reaction conditions.
13
Q
What type of alcohol is oxidised to form an aldehyde?
A
Primary alcohol
The reaction involves converting a primary alcohol to an aldehyde using potassium dichromate and dilute sulfuric acid.
14
Q
What are the reagents used for the partial oxidation of primary alcohols?
A
Potassium dichromate (VI) solution and dilute sulfuric acid
These reagents facilitate the conversion of primary alcohols to aldehydes.
15
Q
What must be done to collect the aldehyde during the oxidation of primary alcohols?
A
Warm gently and distil out the aldehyde as it forms
This process helps to ensure that the aldehyde is collected before it can further oxidise.
16
Q
What is the observation when potassium dichromate is reduced during the oxidation of alcohol?
A
The orange dichromate ion (Cr2O72-) reduces to the green Cr3+ ion
This color change indicates the progress of the oxidation reaction.
17
Q
What is the simplified oxidation equation for propan-1-ol?
A
CH3CH2CH2OH + [O] → CH3CH2CHO + H2O
This represents the oxidation of propan-1-ol to propanal.
18
Q
How should aldehydes be written in a condensed formula?
A
As CHO and not COH
This is important for correctly representing the structure of aldehydes.
19
Q
What is distillation used for in the context of alcohol oxidation?
A
It is used as a separation technique to separate an organic product from its reacting mixture
Distillation maximizes yield by collecting the distillate at the boiling point of the desired aldehyde.
20
Q
Where should the bulb of the thermometer be placed in a distillation setup?
A
At the T junction connecting to the condenser
This ensures accurate measurement of the boiling point of the distillate.
21
Q
Why is water introduced at the bottom of the Liebig condenser?
A
To go against gravity, allowing more efficient cooling and preventing back flow of water
This setup is crucial for effective condensation of the vapors.
22
Q
Why are electric heaters used to heat organic chemicals?
A
Because organic chemicals are highly flammable and could set on fire with a naked flame
Using electric heaters minimizes the risk of fire.
23
Q
How can the yield of distillate be improved during distillation?
A
By cooling the collection flask in ice
This helps to condense the vapor more efficiently, increasing the amount of distillate collected.
24
Q
What is the reaction for the full oxidation of primary alcohols?
A
primary alcohol → carboxylic acid
25
What reagents are used for the full oxidation of primary alcohols?
potassium dichromate(VI) solution and dilute sulfuric acid
26
What conditions are necessary for oxidizing primary alcohols?
use an excess of dichromate, and heat under reflux
27
What observation indicates the reduction of the dichromate ion during oxidation?
the orange dichromate ion (Cr2O7^2-) reduces to the green Cr^3+ ion
28
What is the product formed from the oxidation of propan-1-ol?
propanoic acid and water
29
Fill in the blank: Reflux is used when heating organic reaction mixtures for long periods to prevent _______.
organic vapours from escaping
30
What should never be done to the end of the condenser during reflux?
seal the end of the condenser
31
Why should the end of the condenser not be sealed?
the build up of gas pressure could cause the apparatus to explode
32
What are anti-bumping granules used for in distillation and reflux?
to prevent vigorous, uneven boiling
33
What is the purpose of adding anti-bumping granules?
to make small bubbles form instead of large bubbles
34
What is the chemical equation for the oxidation of propan-1-ol?
CH3CH2CH2OH + 2[O] → CH3CH2COOH + H2O
35
What is the reaction of secondary alcohols?
secondary alcohol → ketone
36
What reagents are used for the oxidation of secondary alcohols?
potassium dichromate(VI) solution and dilute sulfuric acid
37
What conditions are required for the oxidation of secondary alcohols?
heat under reflux
38
What is the name of the ketone derived from propan-2-ol?
Propanone
39
How do ketones typically end in terms of nomenclature?
-one
40
When ketones have 5 or more carbon atoms, what is required in their naming?
a number to show the position of the double bond
41
Provide an example of a ketone with 5 carbon atoms.
pentan-2-one
42
What observation is made during the oxidation of secondary alcohols?
the orange dichromate ion (Cr₂O₇²⁻) reduces to the green Cr³⁺ ion
43
What is the oxidation state of chromium in the dichromate ion?
+6
44
What is the oxidation state of chromium in the reduced form?
+3
45
What happens to ketones under the oxidation conditions of potassium dichromate?
There is no further oxidation of the ketone
46
Why can't tertiary alcohols be oxidized by potassium dichromate?
There is no hydrogen atom bonded to the carbon with the OH group
47
What is the reaction type when alcohols react with dehydrating agents?
Alcohol → Alkene
48
What is a dehydration reaction?
removal of a water molecule from a molecule
49
What reagents are used in the dehydration of alcohols?
Concentrated sulfuric or phosphoric acid
50
What conditions are required for the dehydration of alcohols?
warm (under reflux)
51
What role do the reagents play in the dehydration of alcohols?
dehydrating agent/catalyst
52
What type of reaction is the dehydration of alcohols?
acid catalysed elimination
53
What can happen with some 2° and 3° alcohols during dehydration?
They can give more than one product
54
What is formed when propan-1-ol undergoes dehydration?
Propene
55
Provide an example of a 2° alcohol that can form multiple alkenes.
Butan-2-ol
56
What are the possible products when butan-2-ol is dehydrated?
* But-1-ene
* But-2-ene
57
Which alkene is more likely to be formed from butan-2-ol?
more but-2-ene would be formed
58
What types of isomers can but-2-ene exist as?
E and Z isomers
59
What is a by-product of soap manufacture?
Glycerol
## Footnote
Glycerol is produced during the soap-making process.
60
What is the general reaction for the substitution of an alcohol to form a haloalkane?
Alcohol → Haloalkane
## Footnote
This reaction involves replacing the -OH group of the alcohol with a halogen.
61
What reagents are needed for the substitution reaction of alcohols to form haloalkanes?
Concentrated sulfuric acid and sodium halide
## Footnote
Common sodium halides include NaCl.
62
What is the reaction when sodium chloride and concentrated sulfuric acid are mixed?
NaCl + H₂SO₄ → NaHSO₄ + HCl
## Footnote
This reaction produces sodium hydrogen sulfate and hydrochloric acid.
63
What is the specific example of alcohol reacting with HCl to form a haloalkane?
CH₃CH₂OH + HCl → CH₃CH₂Cl + H₂O
## Footnote
This reaction shows the conversion of ethanol to chloroethane.
64
True or False: A mixture of halide ions with concentrated acid can substitute a halogen onto an alcohol.
True
## Footnote
This process is known as a substitution reaction.
65
Fill in the blank: Various other halogenating compounds can be used to substitute the -OH group for a _______.
halogen
## Footnote
Halogenating compounds include various chemical agents capable of introducing halogens.
66
What is the naming convention for haloalkanes?
Based on original alkane with prefixes: Fluoro for F, Chloro for Cl, Bromo for Br, Iodo for I
## Footnote
Substituents are listed alphabetically in the name.
67
How can haloalkanes be classified?
As primary, secondary, or tertiary depending on the number of carbon atoms attached to the C-X functional group
## Footnote
Primary: one carbon, Secondary: two carbons, Tertiary: three carbons.
68
Define a primary haloalkane.
One carbon attached to the carbon atom adjoining the halogen
## Footnote
This classification indicates the structure's connectivity.
69
Define a secondary haloalkane.
Two carbons attached to the carbon atom adjoining the halogen
## Footnote
This affects the reactivity and substitution patterns.
70
Define a tertiary haloalkane.
Three carbons attached to the carbon atom adjoining the halogen
## Footnote
Tertiary haloalkanes typically undergo different reaction mechanisms.
71
What is a nucleophile?
An electron pair donator, e.g., :OH, NH2, CN-
## Footnote
Nucleophiles are crucial in substitution reactions.
72
What does the mechanism of nucleophilic substitution involve?
Swapping a halogen atom for another atom or groups of atoms
## Footnote
Mechanisms are drawn to outline how a reaction proceeds.
73
What does :Nu represent in a reaction mechanism?
Any nucleophile that has a lone pair and acts as an electron pair donator
## Footnote
The nucleophile attacks the positive carbon atom.
74
What is the significance of the C-X bond strength in substitution reactions?
The rate of substitution reactions depends on the strength of the C-X bond; weaker bonds lead to faster reactions
## Footnote
Fluoroalkanes are very unreactive due to strong C-F bonds.
75
Which iodoalkanes are the fastest to substitute?
Iodoalkanes are the fastest and fluoroalkanes are the slowest
## Footnote
Bond enthalpy values indicate the reactivity order.
76
What type of arrows are used to show the movement of electrons in reaction mechanisms?
Curly arrows with two line heads
## Footnote
These arrows start from a lone pair of electrons or the center of a bond.
77
What does bond enthalpy indicate?
The strength of the bond, measured in kJmol-1
## Footnote
Lower bond enthalpy means easier bond breaking and faster reactions.
78
Fill in the blank: The weaker the C-X bond, the ________ it is to break and the faster the reaction.
easier
79
True or False: Fluoroalkanes are very reactive due to their strong C-F bonds.
False
## Footnote
Fluoroalkanes are actually very unreactive.
80
What is the change in functional group when haloalkane undergoes nucleophilic substitution with hydroxide ions?
haloalkane → alcohol
81
What reagent is commonly used for nucleophilic substitution with haloalkanes?
potassium (or sodium) hydroxide
82
What conditions are required for the nucleophilic substitution reaction with haloalkanes?
In aqueous solution; Heat under reflux
83
What is the type of reagent used in nucleophilic substitution with haloalkanes?
Nucleophile, OH-
84
What is the product formed when i-bromopropane reacts with hydroxide ions?
propan-1-ol
85
What happens to the reaction mechanism if the solvent is changed to ethanol?
an elimination reaction occurs
86
Define hydrolysis in the context of haloalkanes.
the splitting of a molecule (haloalkane) by a reaction with water
87
Why is water considered a poor nucleophile in substitution reactions?
Water reacts slowly with haloalkanes
88
What is the general reaction formula for hydrolysis of haloalkanes?
RCH2CHX + H2O → RCH2CHOH + X• + H+
89
What is formed when aqueous silver nitrate is added to a haloalkane?
silver halide precipitate
90
What indicates the rate of formation of the precipitate in hydrolysis reactions?
the reactivity of different haloalkanes
91
Which type of haloalkane forms a precipitate first with silver nitrate?
iodoalkane
92
What is the relationship between the strength of the C-X bond and the rate of substitution reactions?
The weaker the bond, the easier it is to break and the faster the reaction
93
What color precipitate does AgI form?
yellow precipitate
94
What color precipitate does AgBr form?
cream precipitate
95
What color precipitate does AgCl form?
white precipitate
96
What were CFCs developed for?
use as aerosols, refrigerants, and in air-conditioning
97
What are some properties of CFCs that made them popular for use?
low reactivity, volatility, and non-toxicity
98
What has led to the ban of CFCs?
toxicity of haloalkanes and their detrimental effect on the ozone layer
99
What compounds have been developed as alternatives to CFCs?
HFCs (Hydrofluorocarbons)
100
What is an example of a safer compound used instead of CFCs for refrigeration?
CH3FCF
101
What is now used as a blowing agent for producing expanded polymers instead of CFCs?
CO2
102
What is the chemical formula for ethyne?
HC≡CH
103
What is the chemical formula for propyne?
CH3C≡CH
104
What is the primary benefit of the ozone (O3) layer?
Filters out harmful UV radiation
105
What causes the formation of ozone in the stratosphere?
Ultraviolet radiation
106
What is the reaction for ozone formation?
O + O2 → O3
107
True or False: The frequency of UV light absorbed by ozone equals the frequency of biologically damaging UV radiation.
True
108
What are the two main sources that catalyze the breakdown of ozone?
* CFCs * NOx from thunderstorms or aircraft
109
Fill in the blank: Ozone in the lower atmosphere is a _______.
pollutant
110
What is the reaction for ozone depletion?
O3 + ultraviolet light → O2 + O
111
What is the relationship between the rate of ozone formation and the rate of ozone removal?
They are equal
112
What is produced when C-Cl bonds in chlorofluorocarbons (CFCs) break down?
Chlorine radicals
113
What is the overall reaction for the decomposition of ozone by chlorine radicals?
Cl° + O3 → ClO° + O2
114
What is the significance of the regenerated chlorine radical in ozone depletion?
It can destroy many thousands of ozone molecules
115
What alternative compounds have been developed to replace CFCs?
* HFCs (Hydrofluorocarbons) *
116
Why are HFCs considered safer than CFCs?
They do not contain the C-Cl bond
117
What is a concern regarding CFCs even after legislation was enacted to ban them?
CFCs are still entering the atmosphere and are used in some countries
118
What is the lifetime of CFCs in the atmosphere?
Long lifetime
119
What is the general formula of an alcohol?
CnH2n + 1OH
120
What are the bonds in an alcohol?
Bonds between atoms are covalent
121
Structure of primary alcohol
122
Structure of secondary alcohol
123
Structure of tertiary alcohol
124
Describe the boiling points of alcohols
Alcohols have a higher boiling point than similar molecular mass alkanes
This is due to the presence of intermolecular hydrogen bonding so more energy is required to seperate the molecules
125
What does greater branching in an alcohol mean?
Lower intermolecular forces
126
What are the solubility properties of alcohols?
Low molecular mass alcohols are soluble in water due to hydrogen bonding between the 2 molecules - heavier alcohols are less soluble
127
What are the solvent properties of alcohols?
Alcohols are themselves very good solvents, they dissolve a large number of organic molecules - this is because of the polarity of the OH group attracts other molecules
128
Do alcohols combust more readily than their hydrocarbon equivalents?
Yes - they are added to petrol to increase rage efficiency of combustion
129
How many carbons is a primary alcohol bonded to?
1
130
How many carbons is a secondary alcohol bonded to?
2
131
How many carbons is a tertiary alcohol bonded to?
3
132
What is the usual reagent when oxidising alcohols?
Acidified potassium dichromate (VI) (CrO72- / H+)
133
What colour does acidified potassium dichromate change from?
Orange then turns to green when reacted
134
What are primary alcohols oxidised to?
Oxidised to aldehydes with distillation and then carboxylic acids with reflux
135
What are secondary alcohols oxidised to?
Easily oxidised to ketones with distillation or reflux
136
What are tertiary alcohols oxidised to?
Not oxidised to anything
137
What is the process for primary alcohols being oxidised to aldehydes?
Distillation -
The alcohol is dripped into a warm solution of acidified potassium dichromate
Aldehydes have low boiling points - no hydrogen bonding so distill of immediately
If it did not distill off it would be oxidised to the equivalent carboxylic acid
To oxidise an alcohol straight to the acid, reflux the mixture
138
Diagram for distillation of a primary alcohol to an aldehyde
139
Diagram for an aldehyde being oxidised to become a carboxylic acid
140
What can secondary alcohols only be oxidised into?
KETONES
141
What is the reagent for elimination of water from an alcohol?
Concentrated sulphuric acid or concentrated phosphoric acid
142
What are the conditions for elimination of water from an alcohol?
Reflux at 180oC
143
What is the product for elimination of water from an alcohol?
Alkene
144
What is the equation for elimination of water from an alcohol? (Example)
C2H5OH(l) —-> CH2 = CH2(g) + H2O(l)
145
Diagram for the elimination of water from an alcohol
146
Diagram for elimination of water from an unsymmetrical alcohol
147
What are the reagents for bromination of alcohols?
Sodium bromide and concentrated sulphuric acid
148
What are the conditions for bromination of alcohols?
Reflux
149
What is the product of bromination of alcohols?
Haloalkane
150
What is an example of an equation for bromination of alcohols?
C2H5OH(l) + NaBr(aq) —-> C2H5Br(l) + NaOH(l)
151
Diagram of the equation for bromination of an alcohol
152
Why are haloalkanes reactive?
Because they are electronegative - forms a positive dipole on the carbon and a negative dipole on the halogen as they are more electronegative
The positive dipole carbon atom can be attacked by reagents that are electron rich (nucleophiles)
153
What is a nucleophile?
Can donate a pair of electrons
154
Diagram for nucleophyllic substitution of an haloalkane via hydrolysis
155
What does the rate of nucleophilic substitution depend on?
The strength of the carbon halogen bond
C-I bond is the longest and weakest so most readily undergoes nucleophilic substitution - the ROR involving iodoalkanes is the highest
156
What is the method for relative rates of hydrolysis of haloalkanes?
157
What are CFCs
Hydrocarbons that contain a carbon to chlorine bond - these destroy the ozone layer
158
Diagram for free radicals being produced by CFCs
159
Diagram for free radicals reacting with ozone
160
Full equation for ozone being destroyed
2O3 —-> 3O2
161
How was the problem with CFCs resolved?
Chemists produced HFC gases where the carbon to fluorine bond is stronger so isn’t broken by uv rays and no free radicals are produced
162
What is the method for separating an alkane from water and drying it?
Collect 10ml of the alkane and water mixture
Pour the mixture into a separating funnel, ensuring the tap is closed and stopper it
Shake the funnel and leave it on the clamp stand
Once two layers have formed, remove the stopper
Open the tap and drain the lower layer then dispose of the water
Add anhydrous calcium chloride (drying agent) in small amounts to the alkane while swirling until it stops clumping
After 20 mins filter the drying agent
163
Method for recrystallising an organic solid from a solution
1. Connect the Büchner funnel to the vacuum flask
2. Connect the vacuum flask to a tap and test it has suction
3. Place a filter paper into the Büchner funnel
4. Collect 50cm3 of the hot benzoic acid solution in a beaker and place it into an ice bath for about ten minutes to allow it to recrystallise
5. Pour the benzoic acid solution into the Büchner funnel
6. Chill some distilled water and pour a very small amount over the crystals whilst in the funnel to rinse them
7. Remove the filter paper and funnel and leave to dry
164
Diagram for method for recrystallising an organic solid from a solution
