Alcohols 4.2.1 Flashcards
Define functional group
A group of atoms that determines the substances chemical properties.
What is the general formula for alcohols (aliphatic alcohols with one OH group only)
CnH(2n+2)O
What are phenols?
Aromatic alcohols, they have an alcohol group directly attached directly to the benzene ring.
What are the two possibles names that you can use for alcohols when naming them? When would you use each?
‘Ol’- when it is the only functional group eg. Butan-1-ol (suffix)
‘Hydroxy’ - when there is another function group eg. 2-Hydroxy propanoic acid. (Prefix)
What are the five main uses for alcohols?
- Solvents
- Petrol additive to improve combustion
- Feedstock - in the production of other organic chemicals
- Drinks
- Fuels - alcohols have high enthalpies of combustion
Why can alcohols make hydrogen bonds?
Alcohols can make hydrogen bonds with water molecules and with each other because they have H bonded to an electronegative O.
How do hydrogen bonds affect volatility?
They reduce volatility.
What is volatility?
How easy it is to turn something from a liquid to a gas
Why type of IMF is most often present between ethanol molecules?
Hydrogen bonding
Why might ethanol have a higher boiling point than ethane?
Ethane has induced dipole dipole forces which are the weakest type of IMF whereas ethanol has hydrogen bonding which is the strongest type of IMF. So more energy is required to break the IMF in ethanol.
Why does an increase in chain length affect the boiling point? What effect does it have to the boiling point?
An increase in chain length means that there is an increase in the number of electrons and surface contact so there are more induced dipole dipole forces making it stronger and therefore more energy is required to break them.
Why are alcohols soluble?
Alcohols have a tendency to be water soluble because they can form hydrogen bonds with water.
How does chain length affect solubility?
Solubility decreases as the hydrocarbon chain increases in size, as the OH group has less influence and the solubility of the longer hydrocarbon chain becomes more dominant.
Which molecule would you expect to be more soluble; ethan-1,2-diol or ethanol? Why?
Ethan-1,2-diol as it has more OH groups so it will therefore require twice as much energy to break the hydrogen bonds. (Twice as many H bonds due to another OH group).
Match up the following alcohols with their solubility:
C8H18O Completely miscible
Butanol 9.00
Methanol 0.0540
C5H12O. 0.600
1C
2B
3A
4D
How do we measure solubility?
In grams of alcohol per 100g of water.
What are the three types of alcohols?
Primary alcohols
Secondary alcohols
Tertiary alcohols
State what feature each of these types of alcohols must have:
Primary alcohol
Secondary alcohol
Tertiary alcohol
Primary alcohol - the OH group is attached to a C with at least 2 H atoms on it and one alkyl group. (end of a molecule)
Secondary alcohol - the OH group is attached to a carbon atom with only one H atom. (OH is not at the end of a molecule, no branching)
Tertiary alcohol - the OH group is attached to a carbon atom with no H atoms on it. (Branching in the middle of a molecule)
What are the two types of combustion?
Complete
Incomplete
Write an equation for both the complete and incomplete combustion of ethanol.
Complete: C2H6O + 3O2 ➡️ 2CO2 + 3H2O
Incomplete: C2H6O + 2O2 ➡️ 2CO + 3H2O
What happens to an alcohol when you add concentrated H2SO4 or H3PO4 (with heat under reflux)?
An alkene and water is formed.
What do we mean when we say dehydration of an alcohol? What type of reaction is this?
To remove water from a molecule.
Elimination reaction.
THIS IS NOT A CONDENSATION REACTION!!
Ethanol can be dehydrated, write a fully balanced equation for the dehydration of ethanol. Use structural formula.
CH3CH2OH ➡️ CH2CH2 + H2O
What are the conditions and reagents for the oxidation of primary and secondary alcohols?
Reagent: acidified dichromate (H+/Cr2O7) (potassium dichromate in dilutive acid)
Conditions: Heat; reflux or distillation.
What would be formed if you added potassium dichromate and sulphuric acid to a primary alcohol? (Distillation)
An aldehyde would be formed
What is the functional group for aldehydes and what is the suffix?
=O
Nal
What colour changed would be seen as the alcohol turns to an aldehyde? (When adding acidified potassium dichromate)
Orange to green
Why is there a colour change when you add potassium dichromate?
Dichromate is being reduced to chromium.
What will happen if you took the aldehyde and put it under reflux (further oxidation)?
A carboxylic acid would be formed.
What is formed if a secondary alcohol is oxidised?
A ketone would be formed.
What happens when you oxidise a tertiary alcohol?
Tertiary alcohols cannot be oxidised as there are no hydrogen atoms directly attached to the carbon contains the OH.
What equation would you use to show how a primary alcohol goes to a carboxylic acid?
Primary + 2O ➡️ carboxylic acid
Reflux
How can we use alcohols to form haloalkanes? Write an equation.
NaX
Alcohol ➡️ Haloalkane + Water
H2SO4
