14 Alcohols Flashcards
(31 cards)
What is an alcohol?
(1 mark)
A compound that contains hydroxyl (OH) group(s).
Why are alcohols polar and what does this cause?
(4 marks)
Difference in electronegativity between delta negative O and delta positive H.
This means hydrogen bonds can be formed
and melting and boiling points are higher,
due to stronger intermolecular forces.
Describe the trend in solubility in alcohols.
(3 marks)
As the hydrocarbon chain length of the alcohol increases, solubility decreases
because the influence of the hydroxyl group becomes relatively smaller,
decreasing the interactions with water molecules.
What is a primary alcohol?
(1 mark)
When the carbon bonded to the hydroxyl group is attracted to one other carbon atom.
What is a secondary alcohol?
(1 mark)
When the carbon bonded to the hydroxyl group is attracted to two other carbon atoms.
What is a tertiary alcohol?
(1 mark)
When the carbon bonded to the hydroxyl group is attracted to three other carbon atoms.
Describe the trend in boiling point of alcohols.
(3 marks)
Boiling point increases as the length of the carbon chain in the alcohol increases.
This is because the induced dipole-dipole interactions become stronger,
therefore more energy is required to overcome the intermolecular forces,
so the boiling point is higher.
Why is propane-1,2,3-triol more soluble in water than propan-1-ol?
(4 marks)
Propane-1,2,3-triol has three hydroxyl groups.
Propan-1-ol has one hydroxyl group.
Propane-1,2,3-triol has more hydroxyl groups to form hydrogen bonds with water molecules.
The more hydrogen bonds formed between a molecule and water, the greater the solubility.
What is the suffix for alcohols?
(1 mark)
-ol
What shapes do alcohols form?
(2 marks)
Pyramid-like
Bent
What should be included in a diagram showing hydrogen bonds?
(4 marks)
The HOH should be in a straight line
Partial charges
Line pair of electrons (on the oxygen)
Hydrogen bond should be labelled
Do lone pairs or bonding pairs repel more?
(1 mark)
Lone pairs
State and explain the HCH and COH angles in ethanol- might need paper.
(6 marks)
HCH:
4 areas of electron density
4 bonding pairs
Repel equally
109.5 degree bond angle
COH:
4 areas of electron density
2 bonding pairs, 2 line pairs of electrons
Lone pairs repel more
104.5 degree bond angle (109.5 - (2.5 x 2))
Describe the combustion of alcohols. (4 marks)
Burn completely
In a plentiful supply of oxygen
To produce H2O and CO2
Exothermic reaction
How are primary and secondary alcohols oxidised? (3 marks)
Using oxidising agents
Potassium dichromate
And dilute sulphuric acid
If an alcohol os oxidised, what colour change is expected and why? (3 marks)
Orange to green
Redox reaction takes place
To produce water and chromium ions
Describe how aldehydes are prepared. (3 marks)
Gently heating primary alcohol
With potassium dichromate and dilute sulphuric acid
The aldehyde is distilled out of the mixture as it forms
Why is the aldehyde distilled out of the mixture as it is formed? (2 marks)
To prevent any further reaction with the oxidising agent
To ensure the aldehyde is formed rather than the carboxylic acid
Describe how carboxylic acids are prepared. (2 marks)
Primary alcohol is heated strongly under reflux (with excess potassium dichromate and dilute sulphuric acid).
When producing carboxylic acids, why is heating under reflux used? (1 mark)
It ensures that any aldehyde formed initially in the reaction also undergoes oxidation to produce the carboxylic acid.
What is produced when a primary alcohol is partially oxidised? (1mark)
Aldehyde
What is produced when a primary alcohol is fully oxidised? (1 mark)
Carboxylic acid
What is produced when a secondary alcohol is oxidised? (1 mark)
Ketone
How are ketones produced? (2 marks)
Heating secondary alcohols
Under reflux (with potassium dichromate and dilute sulphuric acid).
