Alcohols Flashcards
What are some uses of Alcohols?
-Cleaning solvents
-Ethanol is ‘alcohol’ in alcoholic drinks
- Ethanol is commonly used as a solvent in the form of methylated spirits
-A ‘’feedstock’’ to produce other chemicals
-An ‘’oxygenate’’ addictive to petrol
- Methanol is used as a petrol additive to improve combustion and is increasing important as a feedstock in the production of organic chemicals
What is the Alcohol functional group called?
Hydroxyl group
Alcohol group
What is the Alcohol functional group?
OH
What is the simplest alcohol, and the next simplest one?
-simplest alcohol= methanol CH3OH, the next member being ethanol CH3CH2OH and so on…
What is the general formula for Alcohols?
CnH2n+1OH
OR
ROH where R is an alkyl group
What states are most Alcohols at room temperature?
At room temperature most Alcohols are liquid
Name the first 3 Alcohols
Methanol
Ethanol
Propan-1-ol
What is the Shortened structural formula for Methanol? And what is the Molecular formula?
CH3OH
CH4O
What is the Shortened structural formula for Ethanol? And what is the Molecular formula?
CH3CH2OH
C2H6O
What is the Shortened structural formula for Propan-1-ol? And what is the Molecular formula?
CH3CH2CH2OH
C3H8O
What is the Shortened structural formula for Propan-2-ol? And what is the Molecular formula?
CH3CH(OH)CH3
C3H8O
Alcohols can be classified as what?
Primary, Secondary or Tertiary
How do you know the classification of an Alcohol?
-Locate the carbon atom to which the OH group is attached and
count number of Hydrogen atoms and alkyl groups attached to the carbon atom that contains the alcohol functional group
What are the 2 simplest alcohols in the alcohol homologous series?
Methanol and Ethanol- they are both primary alcohols
How do you classify a primary Alcohol?
In Primary Alcohol= -OH group is attached to a Carbon atom that is attached to 2 hydrogen atoms and 1 alkyl group
What is an exception to the classification of a primary Alcohol and why?
Exception= Methanol= primary alcohol however has 3 hydrogen atoms and no carbon atoms attached but is still classified as primary alcohol
How do we classify a secondary Alcohol?
-Secondary Alcohol= -OH group is attached to a Carbon atom that is attached to 1 Hydrogen atom and 2 alkyl groups
Examples of a primary Alcohol
Methanol and Ethanol
Examples of Secondary Alcohol
Propan-2-ol and Pentan-3-ol
How do we classify Tertiary Alcohols?
-OH group is attached to a carbon atom that is attached to 0 hydrogen atoms and 3 alkyl groups
Give examples of Tertiary Alcohols
2-methylpropan-2-ol
2-methylbutan-2-ol
= both are tertiary alcohols
Why do we need to be able to classify alcohols?
In order to predict how alcohol will react with oxidising reagent
What are the rules for naming Alcohols?
Use 3-methylbutan-2-ol as an example
1) Find the parent chain and use the alkane name eg. Butane
2) Replace the final “e” with “ol” eg. Butanol
Introduce a number (if needed) into the middle of the name eg. Butan-2-ol
3) Add branch names using usual rules eg.
3-methylbutan-2-ol
Melting point, boiling point, solubility and viscosity depends on what of the alcohols?
the intermolecular forces
Density depends on what of alcohols?
The structure of the molecule (straight chain or branched)
3 test tubes contain 3 alcohols: Explain trend in viscosity
Propan-1-ol
Propane-1,2-diol
Propane-1,2,3-triol
Relationship with viscosity= Intermolecular forces= Hydrogen bonds hold molecules together, Molecules with more OH molecules form more hydrogen bonds between molecules- they separate less easily, and the liquid is more viscous. So Propane-1,2,3-triol would be more viscous than Propan-1-ol
The properties of alcohols are influenced by what?
their ability to form Hydrogen bonds
Complete the blank spaces with your knowledge of Alcohols:
Alcohols are____ __________ and have a higher_______ ______ + greater _____ ___________ than alkanes e.g. if ________ compared to _______
-Alcohols are less volatile and have a higher melting point + greater water solubility than alkanes e.g. if methanol compared to methane
As the carbon chain increases what happens to the differences between alcohols and alkanes? Why?
Differences between physical properties of alkanes and alcohols becomes smaller as the carbon chain length increases considering the affect of the polarity of these bonds on the intermolecular forces
Why is the boiling point of Alkanes lower than the boiling points of Alcohols?
Alkanes=
-non-polar bonds as electronegativity of H and C are very similar
-Alkane molecules are therefore non-polar
-IMF between non-polar molecules= weak LDF
-less energy is needed to overcome IMF
-have lower boiling points than alcohols
Why is the boiling point of Alcohols significantly higher than the boiling points of Alkanes?
Alcohols:
-have polar O-H bonds due to difference in electronegativity of O and H atoms
- Alcohol molecules are therefore polar
-contain very strong Hydrogen bonding between polar O-H groups of different molecules e.g., 2 ethanol molecules
-To change from liquid to gas Hydrogen bonds must be broken between molecules
-requires large amount of energy, so alcohols have larger boiling points than alkanes
Compare the Boiling point of an Alcohol to an Alkane.
(6 Marks)
Alkanes=
-non-polar bonds as electronegativity of H and C are very similar
-Alkane molecules are therefore non-polar
-IMF between non-polar molecules= weak LDF
-less energy is needed to overcome IMF
-have lower boiling points than alcohols
VS
Alcohols:
-have polar O-H bonds due to difference in electronegativity of O and H atoms
- Alcohol molecules are therefore polar
-contain very strong Hydrogen bonding between polar O-H groups of different molecules e.g., 2 ethanol molecules
-To change from liquid to gas Hydrogen bonds must be broken between molecules
-requires large amount of energy, so alcohols have larger boiling points than alkanes
Why do Alcohols have lower volatility than Alkanes even if they were to have the same number of carbon atoms.
-Liquid state= IMF Hydrogen bonding hold alcohol molecules together
-these bonds must be broken to change liquid alcohol to gas
-requires more energy than overcoming weaker LDF in alkanes
-So, alcohols have lower volatility than alkanes with the same number of carbon atoms
Why are compounds with low boiling point volatile? (2 marks)
Because they are easily converted from liquid to gas
Why are alcohols not that volatile
-Liquid state= IMF Hydrogen bonding hold alcohol molecules together
-these bonds must be broken to change liquid alcohol to gas
-requires more energy than overcoming weaker LDF in alkanes
-So, alcohols have lower volatility than alkanes with the same number of carbon atoms therefore a higher boiling point
The higher the boiling point the lower the….
Volatility
Describe the solubility of alkanes
-Alkanes= non-polar molecules – cannot form hydrogen bonds with water
Are Alcohols soluble and why?
Alcohols e.g., methanol and ethanol= completely soluble in water as Hydrogen bonds form between Polar -OH group of the alcohol and the water molecules
As the carbon chain increases what happens to the solubility of the alcohols?
As the Hydrocarbon chain increases in size, the influence of -OH groups becomes relatively smaller, and the solubility of longer chain alcohols becomes more like that of hydrocarbons= solubility decreases
What is Markownikov’s Rule?
States that if a molecule H-X adds to an unsymmetrical alkene, the H always adds on to the side that has the most hydrogens, as this forms the most stable carbocation intermediate
DO NOT USE OR LEARN THIS EXAMPLE
e.g. if reacting 2chloropropene with HBr
- the H will go on the Carbon that already has the most hydrogens on and the Br will have to go anywhere else available== to create most stable carbocation intermediate
Apart from making Alcohols by reaction of an alkene with steam, how else can we make alcohols?
Made by the fermentation of sugars from plant carbohydrates
-Room temperature, anaerobic conditions, enzyme catalyst
E.g.,
C6H12O6 —-> 2C2H5OH + 2CO2
What is the equation for the complete combustion of alcohols?
Equation for complete combustion: fuel + oxygen —-> carbon dioxide + water
What is the equation for the incomplete combustion of alcohols?
Equation for Incomplete combustion: fuel + oxygen —->carbon monoxide + water
Write a balanced Equation for the complete combustion of Ethanol:
CH3CH2OH + 3O2 ——-> 2 CO2 + 3 H2O
Write a balanced Equation for the incomplete combustion of Ethanol:
CH3CH2CH2OH + 3 O2——> 3 CO + 4 H2O
When do alcohols burn completely? And what do they produce when this happens?
Alcohols burn completely in a plentiful supply of oxygen to produce CO2 and water
The reaction of Ethanol reacting with oxygen to form carbon dioxide and water is what type of a reaction? Why?
The reaction of Ethanol with oxygen to form carbon dioxide and water=== exothermic reaction, releasing large quantity of energy in the form of heat
As the no. of C increases in alcohol chain what happens to quantity of heat released during complete combustion?
-As number of carbon atom in alcohol chain increases= quantity of heat released per mole also increases
What alcohols can we oxidise using Solution of Potassium dichromate (VI), K2Cr2O7 acidified with dilute sulphuric acid= H2SO4 ?
-Primary+ Secondary Alcohols can be oxidised by oxidising agent
How do we know if an alcohol has been oxidised after adding oxisidsing agent to it?
If alcohol is oxidised= orange solution containing dichromate (VI) ions is reduced to a green solution containing Chromium (iii) ions
Primary Alcohols can be oxidised into what 2 things?
Aldehydes or Carboxylic acid
Primary alcohols can be oxidised to either aldehydes or carboxylic acids. How do we control which one is produced?
By controlling the conditions under which alcohol is oxidised
Product of oxidation depends on what?
reaction conditions used ( because aldehydes are themselves also oxidised to carboxylic acids)
How is an aldehyde formed?
On gentle heating of primary alcohol + acidified( with dilute H2SO4 added) potassium dichromate (VI) = Aldehyde formed
To ensure aldehyde is prepared rather than carboxylic acid what do we do to the aldehyde made during reaction?
To ensure aldehyde is prepared rather than carboxylic acid, aldehyde is distilled out of the reaction mixture as it forms—-> prevents further reaction with oxidising reagent
How do we prevent further reaction with oxidising agent reacting with aldehyde?
We distil the Aldehyde as it forms from the mixture
How is carboxylic acid formed from a primary Alcohol?
-if primary alcohol heated strongly under reflux with excess acidified potassium dichromate (VI)= carboxylic acid is formed
Why do we use excess acidified potassium dichromate (VI) when turning a primary alcohol into carboxylic acid?
To ensure all the Alcohol is oxidised to form the carboxylic acid
Why do we heat under reflux when oxidising an alcohol to produce carboxylic acid?
Ensures any aldehyde formed initially in reaction also undergoes oxidation to form carboxylic acid
What is the Order of oxidation of primary Alcohols?
Primary Alcohol—> Aldehyde—->Carboxylic acid
What influences the products formed from the oxidation of a primary alcohol?
-Whether a reagent in excess
-Conditions
-Techniques used (distil/reflux)
What are secondary Alcohols oxidised to?Why?
-Secondary alcohols are oxidised to ketones—- not possible to further oxidise ketones using acidified dichromate (VI) ions
How is secondary Alcohol heated to ensure reaction undergoes completion?
-to ensure reaction goes to completion, secondary alcohol is heated under reflux with oxidising mixture/reagent
What happens when secondary alcohol is heated under reflux to the potassium dichromate ions?
-Dichromate (VI) ions change colour from orange to green
Describe the Oxidation of tertiary Alcohols.
tertiary alcohols do not undergo oxidation reactions
What happens to the acidified potassium dichromate when added to tertiary Alcohol?
-acidified dichromate (VI) remains orange when added to a tertiary alcohol
On oxidation what do primary Alcohols turn to?
Primary Alcohol—-> Aldehyde——> Ketone
On oxidation what do secondary alcohols turn into?
Ketones
On oxidation what do tertiary alcohols turn into?
No reaction takes place
What causes Alcohols to oxidise?
-Potassium dichromate K2Cr2O7 is an oxidising agent that causes alcohols to oxidise
How do we write formulae of Aldehydes?
When writing the formulae of aldehydes in a condensed way write CHO and not COH e.g.CH3CH2CHO
Why can’t tertiary Alcohols be oxidised by potassium dichromate?
-Tertiary alcohols cannot be oxidised at all by potassium dichromate: This is because there is no hydrogen atom bonded to the carbon with the OH group
How do you make an Alcohol?
Through reaction of an alkene with steam
