4.2.1/2 : properties and reactions of alcohols Flashcards
What is a primary alcohol?
An alcohol which has the functional group attached to a carbon atom with no more than one alkyl group
Explain the change in boiling points of alcohols as the chain length increases
Boiling points of alcohols increases as chain length increases
- as molecules get longer
- there are more SA contacts
- so stronger LF
- more energy needed to overcome them
= higher boiling points
Explain why the boiling points of alcohols are higher than the corresponding alkanes
- there are hydrogen bonds between the alcohol molecules
- hydrogen bonds are the strongest type of intermolecular force
- so require more energy to overcome than the LFs in the corresponding alkane do
= higher boiling points
What is meant by the term volatile and how does volatility change with boiling point?
Why are alcohols less volatile than their corresponding alkanes?
Volatile = evaporates easily at room temperature and pressure
Volatility increases as boiling point decreases
Alcohols are less volatile than their corresponding alkanes because they have hydrogen bonds
Explain if and why alcohols are soluble in water
Alcohols are soluble in water as both water molecules and the alcohol functional group (-OH) are polar. So alcohol molecules can form hydrogen bonds with the water molecules.
What happens to the solubility as the chain length of an alcohol increases?
As alkyl chain length increases, the solubility of the alcohol decreases
- the alkyl chain cannot form hydrogen bonds and this becomes a larger part of the molecule
How do oxidising agents work and what is a common one used in the oxidation of alcohols?
Oxidising agents provide oxygen to other substances.
Acidified potassium dichromate (VI)(K2Cr2O7/H2SO4)
Explain what happens and what is formed in both the partial and the full oxidation of a primary alcohol
Primary alcohol:
Partial oxidation:
- gently heated with acidified potassium dichromate (VI)
- OH group loses its H atom
- and it is partially oxidised to an aldehyde
- it is distilled immediately to prevent any further reaction
Full oxidation:
- heated strongly under reflux with excess (to ensure all of the alcohol reacts) acidified potassium dichromate (VI)
-full oxidation occurs to form a carboxylic acid
What is reflux?
Constant boiling and condensing of a reaction mixture - ensures reaction goes to completion as fully as possible without losing reactants/products as vapour to the air
What happens in the oxidation of secondary and tertiary alcohols?
Secondary alcohols oxidise to form ketones
Tertiary alcohols do not oxidise
What would you observe in the oxidation of alcohols?
Colour change orange -> green
What is the general formula of an alcohol?
CnH2n+1OH
What is esterification?
A chemical reaction used to make an ester
What are esters and what are they used for?
Esters are organic compounds that contain a -COOR functional group
They are used in the manufacture of foods as they have a pleasant fruity smell
Small molecule esters are used in industry as powerful solvents
Describe what happens during the esterification of alcohols
Carboxylic acid + alcohol <-> ester + water
This is a reversible reaction, has a slow rate and happens in the presence of an acid catalyst
During the reaction
- the O-H bond in alcohol and the C-O bond in the carboxylic acid are broken
- new bonds are formed between the H and O-H to form water
What ester is produced when reacting ethanoic acid and methanol?
Methyl ethanoate
What is dehydration?
Dehydration is a type of elimination reaction in which water is lost from an organic compound. A strong acid catalyst and heat (170) are needed (under reflux)
What are the reaction conditions used in the halide substitution with
Cl-
Br-
I-
HCl
NaBr/H2SO4
NaI/H3PO4
Would you expect the solubility of CH3OCH3 in water to be greater, less or the same as ethanol?
Less - the C-O bond has a permanent dipole, but this is not as polar as the O-H in ethanol so CH3OCH3 cannot form hydrogen bonds with water molecules
Write an equation for the complete combustion of propan-1-ol
C3H7OH(l) + 4.5O2(g) -> 3CO2(g) + 4H2O(l)
Name the secondary alcohol which requires 6 moles of oxygen for complete combustion per mole of alcohol combusted
Butan-2-ol
Explain why the oxidation of alcohols cannot be carried out in an open round-bottomed flask
Alcohols are volatile
